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Copyright@ 1989 by the National R~ng ContractorsAssociation. All rights reserved. No part of this workcan be reproduced without prior written permissionof the publisher.

FOREWORD

The Handbook of Accepted Roofing Knowledge isdesigned to provide designers, specifiers, owners, con-sultants and roofing contractors with information on thedesign and installation of quality roof systems.

These practices represent a consensus of opinion of roof-ing contractors throughout the country. Application tech-niques may vary according to climatic conditions. andeach geographical area may employ "area practices"that are sound and time-proven. We do not mean to im-ply by any exclusion that proven area practices areunsatisfactory.

Roofing technology is currently experiencing revolution-ary changes. Recent problems have stimulated techni-cal research and investigations that are expanding ourknowledge of roof systems. In the interest of brevity, someminor technical points have been excluded from this text.If questions arise, designers are encouraged to contactthe National Roofing Contractors Association (NRCA)members in their geographical area for specific advice.

The Built-Up Roofing Committee of the Asphalt RoofingManufacturers Association congratulates NRCA for thepreparation and publication of this Handbook of kcept-ed Roofing Knowledge, an important contribution to thebuilt-up roofing industry.

TABLE OF CONTENTS

PageI. PRE-ROOFING CONFERENCE. . . . . .. 1II. STORAGE AND HANDLING. . . . . . . . .. 2

III. TEMPORARY ROOFS 3

IV. WEATHER CONSIDERATIONS. . . . . . .. 4V. DECK AND STRUCTURAL DESIGN. .. 5

VI. SLOPE AND DRAINAGE 7

VII. EXPANSION JOINTSANDAREADIVIDERS 10

VIII. MECHANICAL CURBS ANDPENETRATIONS 12

IX. PREFORMED ROOF INSULATION. . . . .14

X. VAPORRETARDERS 17

XI. LIGHTWEIGHT INSULATINGCONCRETE DECKS 19

XII. POURED GYPSUMCONCRETE DECKS 20

XIII. PRECAST PLANK DECKS. . . . . . . . . . . . 21

XIV. PRECAST/PRESTRESSEDCONCRETE DECKS 22

XV. REINFORCED CONCRETE DECKS. . . .23

XVI. STEELDECKS 24

XVII. THERMOSETTING INSULATINGFILLS. . . . . . . . . . . . . . . . . . . . . . . . . .. .26

XVIII. WOOD-PLANK ORPL~D DECKS.. ... ... 27

XIX. ROOFMEMBRANES 29xx. BITUMENS 32

XXI. WATER CUTOFFS ANDWEATHER PROTECTION 36

XXII. FLASHING AND CANTS 37

XXIII. SURFACING AND AGGREGATE. . . . . . .39

XXIV. QUALITY ASSURANCE ANDTEST CUlS ...40

...43

.. .44

.46

.47

.48

71

.71:

.TJ

.74

.75

76

,77

.78

.79

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xxv. REROOFING XXVI. INSPECTION AND MAINTENANCE .

XXVII. FACTORY MUTUAl (FM) ANDUNDERWRITERSLABORAroRIES (UL) XXVIII. ro THE OWNER AND DESIGNER.

GLOSSARY NRCA CONSTRUCTION DETAILS

Detail D Light-Metal Roof Edge. .Detail E Base Aashings for

Non-Wall SupportedDecks .

Detail J Light-Metal Parapet Cap.Detail K-1 Expansion Joint. . . . . . .Detail L-1 Area Divider. . . . . . . . . .DetaIl M-1 Mechanical Equipment

Stand. . . . . . . . . . . . . . . .Detail M-2 Insulated Deck

SteelFrarne Detail N Curb Detail for Rooftop

Air Handling Units. . . . .Detail R Piping Through

Roof Deck Detail T Plumbing Vent Flashing .

Detail U Clearances for Multiple

Pipes. . . . . . . . . . . . . . . .

DetailW-2 Roof Drain Detail X Crickets ; Detail Y Gauge or Thickness

Guide. . . . . . . . . . . . . . . .

. .81

. .82

..83

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I. PRE-ROOFING CONFERENCE

A pre-roofing conference, attended by the owner, archi-ted, general contractor, deck contractor, mechanical con-tractor and the roofing contractor, should be scheduledwell in advance of ordering materials and beginning work.If a roof bond is required, a representative from the roof-ing materials manufacturer should be present. A writtenrecord should be made of the proceedings and shouldbecome a part of the job record. If the roofing contractordiscovers roof problems in his inspection of the roof, asecond, pre-work inspection should be held.

The architect's specifications, roof plans and all roof andflashing details should be reviewed at the pre-roofing con-ference. Any discrepancies between the architect's andthe manufacturer's specifications should be reviewedand resolved. In the event that certain discrepanciesarise, the manufacturer's representative should be con-sulted to resolve the issue. " FM or UL requirements areincluded in the specifications, these requirements shouldbe carefully reviewed. Building code or architecturaldirectives that are in conflict with these insurance require-ments should be resolved.

The directives listed below should be followed to assurea successful pre-roofing conference:

. Establish trade-related job schedules, including the in-stallation of mechanical equipment.

. Establish roof schedules and work methods that willprevent roof damage.

. Require that all penetrations and walls be in place priorto inStalling the roof.

. Establish those areas on the job site that will be desig-nated as work and storage areas.

. Establish weather and working temperature conditionsto which all parties must agree.

. Establish the conditions for which a temporary roofwould be used and who will pay for its cost.

1

III. TEMPORARY ROOFS

Frequently, construction pressures lead to the inStalla-tion of roofing materials during unsuitable weather con-ditions or ahead of construction schedule. In addition,these pressures sometimes cause roofing materials tobe installed before wood blocking, curbs and penetra-tions, and prior to the erection of walls, all of which maycause roof problems. As an effective means of dealingwith the problems caused by construction pressures, atemporary roof is recommended to allow the applicationof the specified roof membrane in suitable weather and/orto allow other trades to complete their work before thepermanent roof is installed.

. Establish provisions for on-site monitoring after thework is completed.

If changes in these conditions are desired, the party re-questing the change should:. Give written notice of the desired changes to all

parties.. Secure written agreement to the changes from all

parties.

II. STORAGE AND HANDLING

The temporary roof specification (the type and numberof plies) will depend on the watertight integrity requiredfor the building and the length of time before the perma-nent roof will be installed. (After suitable repairs aremade, a temporary roof may be used, if desired, as avapor retarder in the permanent installation.) Generally,if roof insulation is used in the temporary roof, it shouldbe removed prior to the installation of the permanent sys-tem, because any moisture sustained from damage couldbe retained in this insulation, and damage to the perma-nent roof system could result.

If a temporary roof is to be used, the specifICations shouldpositively state:

. That a temporary roof will be required. The type and specification of temporary roof to beused

In addition, consideration should be given to having thecost of the temporary roof itemized in the quoted price.

If there is doubt about the necessity for a temporary roof,it can be bid as an additional alternate on a per-square-foot basis. The decision to use a temporary roof, and overwhat areas it is to be used, can then be made duringthe construction period as weather and constructionschedules dictate. The additional cost of a temporary roof

1. All roof systems should be property stored in a drylocation before application.

2. When materials are stored outside, they should beplaced on platforms that are raised off the groundor roof deck, and they should be covered with water-proof coverings (some which may be shrink~ppedcoverings) that have been properly secured. Cover-ings that are "breathable" (such as canvas) are

preferred.3. All roll materials should be stored on end to prevent

them from becoming deformed or damaged.

4. It is recommended that roofing materials be deliv-ered to the job site just before roof installation whenpossible or stored in closed vans.

5. Roofing bitumens may be stored unprotected on theground. However, moisture, dirt, snow or ice shouldbe removed from roofing bitumens before they are

heated.

6. Lids should be replaced on cans of material storedon the job site.

7. Water-based materials should be protected from

freezing.8. Insulation materials should be handled with care.

9. Some insulation materials are extremely light andmust be weighted in storage to prevent wind damage.

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is far preferable to shortened roof life or roof failure! substantially before placing felts and insulation in thebitumen.

It should be noted that a temporary roof can increase thevalue received from the permanent roof because it al-lows the permanent roof to be constructed during suita-ble weather conditions. A temporary roof can also ac-celerate overall building construction by providing a shel-ter beneath which other trades may complete their work

on schedule.

2. Warm TemperaturesWarm temperatures also present problems in main-taining the proper application temperatures for bitu-mens. In hot weather the applied bitumen will coolmore slowly, which can lead to sticking, making themembrane susceptible to physical damage frommechanical equipment and foot traffic.

No other trade is more directly involved in work-relatedweather considerations than roofing. There are many im-pressions throughout the construction industry aboutsuitable roofing weather. Some restrictions prohibit roof-ing under all but the most ideal conditions. The roofingcontractor is vitally concerned with the limitations im-posed on construction activity by the weather, but hemust respond to "real world" conditions and construc-tion demands. To satisfy construction demands and copewith the limitations imposed by weather, the roofing con-tractor should consider the following guidelines for theapplication of roofing materials during various weather

conditions.

3. WindWind can affect the application of roofing materialsin the following ways:

1 . Hot materials may be blown about.2 . Handling roll materials may become difficult.

3. Wind chill may affect the proper application tem-peratures of materials.

4. Sprays of cold mastics and coatings can becomeairborne and cause damage to surrounding

property.

4. PrecipitationRoofing materials should not be installed if precipi-tation of any kind is occurring.

5. MoistureRoofing materials should not be installed if moisture,snow or ice is present on the roof.

Cold TemperaturesRoofing materials should not be applied unless cor-rect bitumen application temperatures can be main-tained. The heating of asphalt bitumens should con-form to the Equiviscous Temperature range concept(EVT). (See Section XX, Bitumens.) The roofing con-tractor may use insulated heating equipment, insu-lated pumping lines, insulated hot carriers, etc. tomaintain proper bitumen application temperatures.If proper application temperatures cannot be main-tained, however, roof application should cease. Incold temperatures, roofing materials must be embed-ded directly with haste. "Brooming" directly behindthe felt embedment is advised to assist the bondingof the felt. Hot bitumen must not be allowed to cool

V. DECK AND STRUCTURAL DESIGN

Good roof systems depend on the structural integrity ofthe roof deck. To ensure the construction of a quality roofdeck, provisions for the following items should be includ-ed in the deck design:

. Uve loads, such as moving installation equipment,wind, snow, ice, rain, etc.

54

VI. SLOPE AND DRAINAGE. Dead loads, such as topside mechanical equip-ment and the deck itself. Deck strength

. Deflections

. Drainage

. Placement of expansion joints and area dividers. Curb details

. Attachment provisions for the deck

. Rolling construction loads of 300 pounds

All roofs should be designed and built to ensure posi-tive, thorough drainage. (See Positive Drainage in theGlossary.) Ponding water can be detrimental to roof mem-branes and can result in:

. Deterioration of the surface and membrane

. Debris accumulation and vegetation growth. Deck deflections (sometimes resulting in structural

problems). Tensile splitting of water-weakened felts. Difficulties in repair should leaks occur. Ice formation and resulting membrane damage

The following chart shows the typical allowable deckdeflections for various spans under a concentrated loadof 300 pounds. Deflections greater than those listed inthe table may lead to roof problems.

Because every roof has its own specific set of drainagerequirements, either the architect or the structural en-gineer is responsible for including proper drainage pr0-visions in the roof design. The designer should not sim-ply specify a standard 1/8 inch or 1/4 inch of slope perfoot but should make provisions in his design for posi-tive drainage. In order to achieve the necessary slopein his design, he must consider the structural framingof the roof, the deck type, the roof membrane specifica-tion, roof deflections and the building la)Uut. The neces-sity for brevity here prevents a complete explanation ofeach of these considerations. The following brief exam-ples, however, are typical slope and drainage computa-tions.

Deck Deflection~4 feet5 feet6 feet

0.20 inches0.25 inches0.30 inches

Before applying roofing materials, the roofing contractorshould make a visual inspection of the deck surface tosee that it is ready for application. The deck must beclean, smooth, free of wids or depressions and rigid, andit must not deflect excessively under live loads.

If the roofing contractor discovers defects in the surfaceof the deck during this inspection, a second inspectionshould be made prior to roofing by the roofing contrac-tor, the general contractor, the deck contractor and theowner's representative. All defects in the deck at the timeof this inspection should be noted, and correctionsshould be made before beginning work. The trade con-tractor who is responsible for any defects or damage tothe deck should be responsible for making repairs. Jobspecifications should clearly define this responsibility.

Deflection Slopes

Roof deflections are critically important in providing roofdrainage. They should be limited to no more than 1/240of the roof span in order to accommodate the stressesof either concentrated or uniform loading. Drains shouldbe located at points of maximum deflection in the deck(i.e., midspan) if possible and not at points of minimumdeflection (i.e., columns or bearing walls). For example,in Figure 1 a deck span of 50 feet should deflect not more

76

Positive Slopesthan 2-1/2 inches (1/240 of 50 feet) and should havedrains located at midspan in order to provide drainageunder maximum loading conditions. After the drain locations have been selected and the

deflection slopes computed, the designer must provideadditional slope to ensure positive drainage. Becausedrainage must occur under both minimum and maximumloading conditions, an additional minimum slope of 1/8inch per foot should be added to the deflection compu-tation in order to attain a slope that will positively drainthe roof. Thus, to drain the 5O-foot span in Figure 1, wherethe drain is placed at the point of maximum deflection,the designer should provide at least 3.125 inches ofdifferential slope for positive drainage under all loadingconditions. For Figure 2, where the drain is located ata point of minimum deflection, the positive slope requiredis 6.25 inches, which, when added to the 5 inches ofdeflection slope, yields a total required slope of 11.25inches under all loading conditions.

Figure 1

If drains are required to be placed at columns or bear-ing walls, the slope of the roof must be increased in or-der to compensate for the minimum deflections that ex-ist at these locations. The allowable deflection will stillbe 2-1/2 inches, but the designer must provide for 5inches of additional slope at the column or bearing walllocation in order to keep this deck level at midspan un-der maximum loading conditions. (See Figure 2.)

Certain decks, such as precast concrete decks or Iong-span prestressed concrete decks, incorporate camber inanticipation of future loading conditions. The cambermust be considered in the design of the drainage slopesystem. Depending on the structural design of the roofand the placement of drains, the camber may assist orrestrict drainage. (See Figure 3.)

Maintaining a roughly level line between one support anda 2-1/2 inch midspan deflection requires raising the oth-er support 5 inches.

These examples illustrate that the computations for roofslope should be determined by the deflections expect-ed in each particular roof deck and that the commonlyspecified 1/8 inch or 1/4 inch of slope per foot is inade-quate as an absolute specification to attain proper drain-age on all roofs.

-Note: Figures 1,2, and 3 have been exaggerated to helpillustrate drainage conditions more clearly.

98

In providing for drainage, the designer must carefully oon-sider all areas of the roof. Good practice dictates thatthere be no pondlng water. For information on deck de-sign for ponding water conditions, designers may con-sult the American Institute of Timber Construdion (AJTC).the Steel Joist Institute (SJI) or the American Institute ofSteel Construction (AISC). Drainage crickets should beprovided between drains and on the high side of mechan-ical curbs to drain these areas. (See NRCA Construc-tion Details.)

and to prevent these stresses from splitting or ridgingthe roof membrane. Joints in the roof assem~ (the termroof assembly includes the roof deck) must be placedin the same location as the building's structural expan-sion joints (although they may also be required in otherlocations, as discussed in this section). Each of a build-ing's components has varying coefficients of expansionand contraction, and each of them is subjeded to vary-ing temperature changes. In the design and placementof expansion joints, the designer should consider:

. The thermal movement characteristics of thebuilding

. The structural roof deck

. The roof membrane selected

. The climatic conditions to be encountered

Expansion joints must extend across the entire width ofthe roof; they must never terminate short of the roof edgeor perimeter. They should be designed to accommodatecontraction as well as expansion. The expansion jointshould be detailed and constructed to a raised (nominal)height of 8 inches above the roof line. (See NRCA Con-struction Details.) Water drainage should NEVER be at-tempted through or over an expansion joint.

To ensure the proper draining of water in the heaviestrains. the design of drain sizes and drain placementshould be based on either:

. The requirements of the American NationalStandards Institute (ANSI) Standard A 112.21.2

. Building code requirements or

. Maximum rainfall information of the geographicalarea

Drains should be recessed (sumped) below the roof sur-face, and sufficient insulation must remain around thedrains to prevent condensation. This is accomplished bysetting the drain head below the level of the insulationand tapering the insulation down to the drain. (See NRCAConstruction Details.) Regular maintenance should beperformed to prevent clogging of drains. To avoid thedangers of water buildup from clogged drains, the useof auxiliary drains or throughwall scuppers is recom-mended and, in many cases, is a part of building code

requirements.

VII. EXPANSION JOINTS ANDAREA DIVIDERS

Expansion Joints

Roof expansion joints are used to minimize the effect ofthe stresses and movements of a building's components

Roof expansion joints should always be provided at thefollowing locations:

. Where expansion or contraction joints are provid-ed in the structural system

. Where steel framing, structural steel or deckingchange direction

. Where separate wings of "L," "U," "T" or simi-lar configurations exist

. Where the type of decking changes; for example,where a precast concrete deck and a steel deckabut

. Whenever additions are connected to existingbuildings. At junctions where interior heating conditions

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Some equipment may allow moisture to enter the build-ing either from the exterior or from condensation within.It is imperative that mechanical equipment housings bewatertight. Water discharge from mechanical equipmentshould not be allowed on the roof surface.

change. such as a heated office abutting an un-heated warehouse. canopies. etc.

Where movement between vertical walls and theroof deck may occur

Area DividersWhen large mechanical units are used, drainage crick-ets should be provided around the units to allow ade-quate drainage of these areas. Mechanical units shouldnot restrict the flow of water. Adequate space should beprovided between mechanical units, penetrations andwalls so that roofing materials can be installed correctly.

Where expansion joints are not provided. area dividershelp control the thermal stresses in a roof system (theterm roof system does NOT include the roof deck). Theyminimize the transmission of stress from one area of theroof to another by dividing the entire roof area into smallerroof sections. These sections should be of rectangularshape and uniformly spaced where possible. The design-er should determine the respective location and the typeof area divider to be used.

Units using curbs that have built-in metal base flashingflanges are difficult to seal and, therefore, are not recom-mended for use. Composition base flashing should ex-tend a minimum of (a nominal) 8 inches above the roofline. Wood or fiber cants must be provided at any9O-degree angle created by rectangular curbs or projec-tions. Wood nailers should be provided on all prefabri-cated curbs. The composition flashing (base flashing)should be fastened either with 1-inch, solid cap-headnails or with nails driven through tin discs. The nailsshould be spaced approximately 8 inches apart.

An area divider is designed simply as a raised double-wood member attached to a properly flashed wood baseplate that is anchored to the roof deck. (See NRCA Con-struction Details.) Depending on climatic conditions andarea practices, area dividers for attached membrane sys-tems are generally required at 150- to 200-foot intervals.They should be located between structural roof expan-sion joints. They should not restrict the flow of water.

On mechanical units, two-piece metal counterflashingshould be installed over the base flashing. On units thatwill be frequently serviced, the counterflashing shouldextend down over the cant to the roof line so that no baseflashing is exposed.

The use of elastic preformed "control" joints that aredesigned to be installed in the flat plane of the roof isnot recommended because roof system movement mayresult when these units are used. The use of raised curbarea dividers is consistent with good roofing practice. Penetrations around short pipe projections may be

flashed into the membrane by using soft metal or leadflashing with integral flashing flanges stripped into themembrane. Good practice dictates that curbs beplaced around all penetrations; the use of so-called"pitch boxes" or "pitch pockets" around penetra-tions should be avoided because they pose a con-stant maintenance problem. Projections should not belocated in valleys or drain areas. Adequate space shouldbe provided between pipes, curbs and walls to allow forthe installation of roofing materials.

VIII. MECHANICAL CURBS ANDPENETRATIONS

To avoid deflections damaging to the roof, the structuraldesign of the roof should always allow for the concen-trated loading of mechanical equipment. Vibrations fromroof-mounted or joist-mounted mechanical equipmentshould be isolated from the membrane and flashing.

12 13

All curbs, penetrations, roof drains and plumbing pipesmust be in place before installing the roof. Openings torcurbs cut through the roof membrane after the roof hasbeen completed can present a serious bitumen drippageproblem when the membrane is constructed of lowsoftening point bitumen. All curbs should be firmlyfastened to the building structure or to the roof deck be-tore roofing material application. Roof drains, vent pipes,etc. should all be in place prior to roofing and restrainedto prevent damage to the flashings or membrane thatmay occur if mechanical devices are installed over thecompleted membrane.

Mechanical units mounted on pipe standards beneathwhich roofing materials will extend must be mounted toa height sufficiently above the roof to allow room to in-stall the roof system and to make repairs beneath the unit.Heavy loads, such as large mechanical units, should notbe rolled over the completed membrane, as they maycause damage to the roof. A failure in horizontal shearbetween the membrane insulation or deck from theseloads may result in future splitting of the roof. NRCArecommends that mechanical equipment be installed onfully enclosed curbs (not on support stands) to eliminatethe need for reroofing under these units when reroofingbecomes necessary in the future.

See the NRCA Construction Details for recommendedmechanical equipment curb, stand and penetrationflashings.

An ideal roof insulation would have the following theo-retical properties:

. It would be able to withstand the bitumen appli-cation temperatures required for installation of theroof membrane.

. It would have good physical strength, rigidity andimpact resistance.

. It would be incombustible and would be accepta-ble for insurance and building code requirements.

. It would be constructed of materials that will re-sist deterioration.

. It would be moisture resistant.

. It would have a low k-value (thermal conductivity)so that the highest possible A-value (thermal re-siStance) can be obtained in the thinnest possi-ble piece of a particular insulation.. The k-value YX>uld remain constant and would not"drift" higher with age.. Its surfaces would accommodate secureattachment.. It would have dimensional stability under varyingtemperature and moisture conditions.

. It would be manufactured so as to be compati-ble with the roof membrane.

The qualifications listed above would be present in anideal insulation. In practice, however, no single commer-cial product contains all of the ideal properties. Thus, thedesigner should choose materials with properties bestsuited to the specific project.

As a final consideration, it should be noted that helicop-ter placement of mechanical equipment can cause dam-age to the roof system if the helicopter is operated tooclose to the roof surface.

Roof insulations, when used for the control of heat flow,should be installed in two layers (when thickness per-mits) with all joints offset between the upper and lowerlayers. The joints of the insulation should be installed toprovide moderate contact at the joints. The upper layershould be installed with the long dimension of the insu-lation boards placed in a continuous line and the endjoints staggered.

IX. PREFORMED ROOF INSULATION

Roof insulation provides both the insulation for the build-ing and a substrate to which the built-up roofing materi-als are applied. Therefore, it must be compatible with,and should provide support for, the roof membrane.

14 15

Over steel decks, mechanical fasteners should be usedto attach the first layer of insulation. Where possible thefirst layer of insulation should have an insulation valueequal to or lower than that of the second layer. The sec-ond layer of insulation should be laid in moppings of hotasphalt and, normally, should have the greater insula-tion value.

X. VAPOR RETARDERS

All roof insulation should be protected from the elementsbefore, during and after installation. During and after in-stallation, this protection is provided by the immediateinstallation of the roof membrane. On low-sloped roofs.proper membrane application dictates that roofing feltsbe laid perpendicular to the flow of water, beginning atIaN points (or drain points) in the deck. All roof membraneplies should be installed in an unbroken time period;phased construction is NOT recommended. The longdimension of the insulation boards should be laid per-pendicular to the flow of water.

The term vapor retarder refers to a broad range of roof-ing materials that are used to control the flow of watervapor from the interior of the building into the roof sys-tem. Moisture in the form of water vapor generally comesfrom the following sources:

. Construction processes. which include interiorconcrete and masonry. cementitious roof fills,plaster finishes and fuel burning heaters

. Occupancy-generated sources, which includesuch areas as swimming pools; textile. food andpaper plants; and other wet-process industrialplants.

In the generally temperate climate of the United States,during the winter months, water vapor flows upwardthrough the roof system from a heated, more humid in-terior toward a colder, drier exterior. Vapor retarders aremore commonly required in northern climates than insouthern regions, where downward vapor pressure maybe expected and the roof membrane itself becomes thevapor retarder.

Roof membranes should NOT be installed directly to thetopside of any felt-skinned foam-type insulation, includ-ing polyisocyanurate and polyurethane, because of thepotential for blister formations.

As a general guide, vapor retarders should be consid-ered for use when both of two conditions are anticipated:

1 . The outside average January temperature is be-low 40F.

2. The expected winter interior relative humidity is45 percent or more.

Vapor retarders should be installed at a location wherethey will be warmer than the winter design dew-point tem-perature. The dew point should fall within the insulation.It is recommended that moisture relief vents, preferablyone-way vents, be incorporated into the roof system atthe minimum quantity of one vent per 1,000 square feetof roof area (10 roof squares) or less.

When composite board roof insulation polyisocyanuratefoam board roof insulation, polyurethane foam board roofinsulation on phenolic foam insulation is used as the in-sulation substrate, the following is recommended:

. Over the top surface of the insulation, a thin layerof wood fiberboard insulation, perlitic board insu-lation or glass fiber board insulation should beinstalled. The roof membrane should then be ap-plied as specified by the designer.

Performance-type specifications should be avoidedwhen specifying any insulation, as manufacturers' datamay vary considerably. Instead of listing performance-type specifications, the designer should list the ASTMspecification, the thickness requirements and the C-value for any insulation board to be used in the roof con-struction.

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XI. LIGHTWEIGHT INSULATINGCONCRETE DECKS

Roof system vapor retarders generally fall into twoclassifications:

1 . Bituminous membranes, in which a continuousfilm of bitumen serves as the vapor resistant ele-ment. A typical two-ply installation using threemoppings of steep asphalt can provide a vaporretarder that is rated less than 0.005 perms.

2 . Non-bituminous sheet systems, in which thesheet serves as the vapor retarder, and adhesiveis used to seal the laps. These include POIC films,kraft paper and aluminum foil combinations, whichmay provide vapor retarders having permeabilityratings ranging from 0.10 to 0.50 perms. POIC filmsand associated cold-applied adhesives are notrecommended by NRCA because of their suscep-tibility to damage from other components in thesystem, such as the melting of vinyls by hotasphalt.

Lightweight insulating concrete is used for the construc-tion of composite structural decks and as a fill materialover some structural decks. (It is not recommended foruse, however, directly over poured-In-place or precastconcrete decks.) The installation of lightweight insulat-ing concrete requires large quantities of water, and somemoisture will remain in the concrete even after the sur-face is dry. Venting must be provided to allow additionaldrying of the concrete and to prevent the buildup of wa-ter vapor pressure. Either topside venting or undersideventing is advised on all lightweight insulating concretedecks. Topside, one-way venting in the field is preferable.

Wherever vapor retarders are used. they should be con-structed of materials compatible with other roof systemcomponents. It is recommended that the designer payparticular attention to flashing details at edge seals andat all penetrations through the vapor retarder in order toensure the moisture-tight integrity of the vapor retarder.Vapor retarders can be easily punctured and damagedby foot traffic and mechanical equipment. These punc-tures must be carefully repaired prior to the installationof insulation, using a patch that is at least 12 inches largerin each direction than the puncture. In order to properlyinstall and help prevent damage to a vapor retarder sys-tem, the laps must be made on solid bearing. For morespecific information on vapor retarders. see Vapor Retard-ers in the Low-Slope section of the NRCA Roofing andWaterprooflng Manual.

Lightweight insulating concrete decks must have the fol-lowing physical properties:

. A minimum thickness of 2 inches of lightweightconcrete

. A minimum dry density of 22 pounds per cubicfoot (pcf), or a dry density capable of providing afastener withdrawal resistance of 40 pounds perfastener

. A minimum compressive strength of 125 poundsper square inch (pSt")

Lightweight insulating concrete decf<S should be installedaccording to the lightweight insulating concrete manufac-turer's specifications.

The roof membrane should be attached to the lightweightinsulating concrete deck in accordance with the deck ma-terial manufacturer's recommendations. If no recommen-dations are provided, a coated base ply or a vented baseply should be used as the first ply of the membrane andshould be attached to the lightweight insulating concretedeck with approved mechanical fasteners. In no caseshould the base ply of the membrane be attached tothese decks in mopplngs of hot asphalt or by adhe-sives.

1918

.Anditional roof insulation should NOT be installed directlyover lightweight insulating concrete decks, as it will in-hibit the drying of the concrete. However, when above-deck insulation is specified, the insulation should be pro-tected from moisture by a low perm-rated vapor retarderplaced between the lightweight insulating concrete andthe insulation. (See Section X, Vapor Retarders.) The in-sulation must be vented. Smooth-surfaced roof mem-brane systems are generally not recommended for useover lightweight insulating concrete decks.

Roof insulation should NOT be installed directly over newtypoured gypsum concrete decks as it will inhibit the dry-ing of the concrete. However, when above-deck insula-tion is specified, the insulation should be protected frommoisture by a low perm-rated vapor retarder placed be-tween the poured gypsum concrete and the insulation.(See Section X, Vapor Retarders.) The insulation mustbe vented.

Smooth-surfaced roof membrane systems are not recom-mended for use over poured gypsum concrete decks.Roofing materials may be installed as soon as the deckis set and is surface dry (approximately one hour). Afterthe roof is inStalled, the general contractor should pro-vide sufficient ventilation on the underside of the deckand within the building to allow continued drying of thedeck.

NRCA recommends that specifiers consult with mem-brane manufacturers for specific recommendations onrequirements for roofing over lightweight insulating con-crete decks.

XII. POURED GYPSUM CONCRETE DECKS

XIII. PRECAST PLANK DECKSPoured gypsum concrete is used in various combinationswith other building products as a strudural deck. The roofmembrane should be attached to the poured gypsumconcrete deck in accordance with the deck materialmanufacturer's recommendations. If no recommenda-tions are provided, a coated base ply or a vented baseply should be used as the first ply of the membrane andshould be attached to the poured gypsum concrete deckwith approved mechanical fasteners. Venting to the in-terior should be provided and is generally accomplishedthrough the use of a vapor-permeable formboard. If thistype of form board is not employed, topside ventingshould be designed and installed.

Precast plank dec~ are constructed of metal-bound gyp-sum, structural lightweight insulating concrete or cemen-titious wood fiber and are used either as structural deck-ing or in combination with sub-purl ins. Voids and jointsover sub-purlins must be grouted with materials suppliedor recommended by the deck manufacturer and shouldprovide approximately 1/8 inch of slope per foot. Partic-ular attention must be given to the storage and handlinginstructions for these materials. The designer must care-fully consider the concentrated live loads of roof appli-cation equipment in the selection of these dec~. All slabsshould be securely fastened to resist uplift and horizon-tal movements.The gypsum fill should be reinforced with wire mesh. It

should have a minimum thickness of 2 inches, not in-cluding the form board, and should cover the top of bulbtees a minimum of V4 inch. A coated base ply or a vent-ed base ply is generally used as the first ply of the mem-brane and is attached to the gypsum concrete deck withmechanical fasteners. The membrane should NEVERbe installed to gypsum concrete decks in moppingsof hot asphalt or by adhesives.

Precast plank decks should be roofed promptly after in-stallation. The planks may be fragile and should be treat-ed with care. Planks should be installed during weatherconditions that are suitable for the installation of roofingmaterials, or temporary protection should be provided.

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Membrane application to these decks should follow thedeck manufacturer's recommendations. Generally, at-tachment of the base ply with approved mechanical fast-eners is recommended. If insulation is used, a nailablebase ply is required as the attachment layer. Insulationshould then be solidly adhered to the base ply with hotasphalt only. Adequate ventilation of the underside of thedeck during the construction process is mandatory. Inno case should the first ply of the roof membrane bemopped directly to precast planks.

The designer should carefully detail all wood blockingprovisions at roof edges and penetrations to ensure pr0p-er attachment of the membrane and sheet metal. In nocase should the roof membrane be attached directly toprecast/prestressed concrete decks. Preformed roof in-sulation (preferably in two layers) should be installed ontop of the deck before application of roof membranematerials.

When precast walls are used, the designer should care-fully consider the flashing provisions required to proper-ly secure the roof to the precast wall units. Cast-in reglets,which are frequently used for this purpose, are difficultto align properly. When they are not properly aligned,they can hinder the proper installation of counterflash-ing. For this reason the use of cast-in reglets is not recom-mended. In all such flashings situations, considerationshould be given to camber and creep.

XIV. PRECAST/PRESTRESSEDCONCRETE DECKS

Precast concrete units are used as structural roof decks.The manufacturing process of precast concrete units mayproduce units that vary in joint elevation when set inplace. If variations in the elevations of adjacent units ex-ceed 1/4 inch, the deck should be leveled with a fibrouscementitious grout that has been feathered to a slopeof 1/8 inch per foot prior to roofing. Venting for this fillshould be provided. A vapor retarder may be required,depending on the fill material used. (See Section X, Va-por Retarders.) The joints between adjacent units shouldbe filled with a compressible material to prevent drippageof the cementitious fill that is used to level the units.

When precast walls are used, it is recommended that pr0-visions be made for IaN parapet walls. The base flash-ing should be fastened to a vertical wood upright whosehorizontal base is attached to the deck only. After thebase flashing has been attached to the wood upright, themetal wall cap flashing may be installed. Then the coun-terflashing may be attached to the wall cap, extendingdown over the top of the base flashing. This method al-lows lateral movements of the wall without damage tothe base flashing.

Recommendations of the Precast Concrete Institute fordeck installation should be followed. Weld plates shouldbe provided between other structural components andthe deck units and between the deck units themselves.The top surface is sometimes neglected in the castingof precast units. A smooth surface, free of voids anddepressions, should be provided for proper adhesion ofthe roof system. In order to provide adequate drainage,the designer must consider the "bowing" (or verticalcamber) of precast units that occurs in the manufactur-ing process of the units. Depending on structural designand drain placement, the camber may assist or restrictdrainage. (See Section VI, Slope and Drainage.)

XV. REINFORCED CONCRETE DECKS

Reinforced concrete is used as a structural deck. Thepouring process requires large quantities of water, andsome moisture will remain in concrete decks even afterthe surface is dry. Prior to the application of roofingmaterials, the concrete surface must be smooth, leveland free of moisture. The deck contractor is responsiblefor removing sharp ridges or other irregularities in thedeck surface. Wood bk>cking nailers should be designedand provided at all roof perimeters and penetrations for

22 23

fastening the flashings and sheet metal. Concrete cur-ing compounds which are used to finish the deck sur-face must be compatible with the bitumen being used(either asphalt or coal tar bitumen).

sulation manufacturer's specifications. The first layer ofinsulation should be attached with mechanical fastenersaccording to Factory Mutual Data Sheet 1-28. The se-cond layer should be laid with joints offset from the firstlayer and in moppings of hot asphalt.

Reinforced concrete should be primed, and the primermust be allowed to dry prior to the application of roofingmaterials. If roof insulation is to be installed over rein-forced concrete, the insulation and membrane must beprotected from the effects of latent moisture in the con-crete. In northern climates, this is generally accom-plished by using a vapor retarder or a venting sheet. (SeeSection X, Vapor Retarders.) In southern climates,however, vapor retarders are often omitted, and vent-ing of the insulation alone has proved to be adequate.In cold weather, poured concrete is usually protected byinsulative batts or blankets. When these batts or blanketsare removed, the concrete may be cured at the surface,but some moisture will remain inside the concrete deck.In these situations, if subsequent insulation is to be in-stalled, the use of a vapor retarder is recommended toprevent moisture damage to the insulation.

When specifications call for only one layer of insulation,the insulation should be attached with mechanicalfasteners according to Factory Mutual Data Sheet 1-28.

Certain FM or UL requirements for the deck surface andfor the attachment of the insulation may be applicable.The most current FM and UL publications should be con-sulted for specific deck surface and insulation attach-ment requirements. Generally, these requirements placelimitations on the concavity ("cupping") of contactflanges and stiffening ribs. They also require that sidelap fasteners be used to secure steel deck panels to ad-jacent panels. Provisions should be made to have thetop flanges of the steel deck units installed perpendicu-lar to the roof slope. This will allow for the long dimen-sion of the insulation boards to be laid parallel to the steeldeck, as FM requires, and will help to avoid phased con-struction of the roof membrane.

XVI. STEEL DECKS Adequate side lap bearing is necessary to support rigidinsulation boards. To help achieve the proper bearing,the steel deck units should be installed with a maximumhorizontal alignment tolerance of Y4 inch for every 100feet of deck length (i.e., after installation, the deck unitsshould vary in horizontal alignment by no more than Y4inch).

Steel decks should be designed according to the steeldeck manufacturer's specifications and installed accord-ing to the application procedures recommended by theSteel Deck Institute in order to obtain optimum perfor-mance. Decks should be 22-gauge or heavier. Maximumspan recommendations for typical 1-1 /2-inch steel deckswith 6-inch rib spacing are published by Factory Mutual(FM) in Data Sheet 1-28. FM field offices and steel deckmanufacturers should be consulted for advice on themaximum span recommendations for steel decks.

Mechanical fastening of steel deck units to the structur-al steel provides the most positive means of attachment.When steel deck units are spot-welded, the weld materialwill frequently "pop" loose due to improper welding tech-niques or minor flaws in welding. When it is desired thatsteel decks be welded, it is recommended that "puddlewelds" of 1/2 inch or larger, welded into washers andspaced a maximum of 12 inches on center at every sup-port, be used.

Insulation commonly applied to steel decks prior to theapplication of the roof membrane should be applied intwo separate layers where insulation thicknesses per-mit. The first layer should be capable of spanning theflute width of the metal deck in accordance with the in-

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XVII. THERMOSETTING INSULATING FILLS units should be staggered. Because wood can beadversely affected by moisture, wood decks shouldbe constructed of air-dried or kiln-dried lumber andshould be protected from moisture.Thermosetting insulating materials are used as insula-

tive fills over structural decks. They should be installedaccording to the manufacturer's specifications. Thesematerials require compaction by weighted rollers, andthe structural designer must consider the concentratedlive loads of these rollers in the design. When thermoset-ting insulating fill is placed over a metal deck, the deckmust be rigid enough to prevent flexing during the com-paction process. The compacted density of the fill shouldrange between 18 and 22 pounds per cubic foot. Thisdensity is generally attained by compacting the thermo-setting insulating fill in one layer or, if the total thicknessis greater than 6 inches, in two layers. A spray of wateris usually used to cover the surface prior to compaction.The quantity of water in this spray should be kept to aminimum.

Bitumens or adhesives are not generally used to at-tach the membrane to a wood deck. The use ofmechanical fasteners is recommended for the at-tachment of the membrane directly to a wood deck.

A separator sheet of rosin-sized sheathing paper isrecommended for use over wood plank decks.

Note: Caution should be exercised when wooddecks are constructed of wood that has been treat-ed with an oil-borne preservative. When such treat-ed wood is used in the deck, a barrier of rosin paperor similar material shoukj be placed between the roofmembrane and the deck.

Thermosetting insulative fills should be protected frommoisture. Roofing materials should be applied each day,or temporary protection should be provided. The baseply over these fills should be applied in a solid moppingof steep asphalt, and provisions for roof venting shouldbe incorporated into the fill by the designer to releasemoisture vapor. If roof insulation is installed over thesefills, a protective base ply vapor retarder should bemopped to the fill to protect the insulation from substratemoisture and to allow time to install the insulation androof membrane. Wood nailers must be provided at allperimeters and projections through the roof. It ispreferred that aggregate-surfaced roofs be applied overthese fills.

B. Wood Panel Decks - Veneer and Non-VeneerMost building codes require a label on wood panels,assuring that the panel complies with the standardsset forth in the Department of Commerce StandardPS 1-83, for all-veneer plywood, or the American Ply-wood Association Performance Standard PRP-108,for oriented strand board, waferboard, and also all-veneer plywood which does not comply with PS 1-83in certain respects. These are voluntary standards,and producers do not have to meet these standardsin order to sell their products. NRCA recommendsthat wood panel decks be designed and applied inaccordance with the recommendations of the Ameri-can Plywood Association. The wood panels shouldbe interior type (with exterior glue); bear the APAtrademark; and be secured to structural joists eitherby annular threaded nails, ring-shank nails or by sta-ples. (See the sample labels on the following page.)

XVIII. WOOD-PLANK OR PLYWOOD DECKS

Label A is found on all-veneer plywood conformingto PS 1-83. Label B is found on wood panels con-forming to PRP-1OS, which includes oriented strandboard, waferboard, and also all-veneer plywood

A. Wood Plank DecksPlanks for wood plank decks should be (a nominal)1 inch or thicker and of tongue and groove construc-tion. Cracks or knot holes larger than 1h inch in di-ameter must be covered with sheet metal if roof in-sulation is not used. End joints of the wood deck

26 27

wood sheathing with exterior glue as C-DX, the "X"(which refers to Exterior Glue) is not used in labelA. The EXPOSURE 1 classification is typically interi-or type panel with exterior glue.

End joints of the wood panels should be staggeredand supported by framing members, and deck sup-port clips should be installed on the unsupportedsides of the wood panel sheets. Temporary protec-tion should be provided by the installer to prevententry of moisture into the panels. (See Section III,Temporary Roofs.)

A slip sheet of dry sheathing paper is recommend-ed for use over wood plank decks but is not neededover wood panel decks. It is good practice, however,to nail a minimum layer of insulation over wood paneldecks. On panel decks not covered with insulation,a base ply should be mechanically fastened over thewood panel deck (preferably with annular threadednails) to serve as the base ply of the roof membrane.

=APA-P8n8I Grade RATED SHEATHINGSp8n RaI81g 32/16 15/32 INCH ~

EMP(.ure SIZED FOR S~ING~ EXPOSURE 1dassitK:al~ 000 Mil n.-nbef

Code recogM~ 01 - NER.QA387 PHp.", -APA.s Perkwmance-RaIedAPA as a CJJMty PanS STandard8S9Jr~ 99Br-=v

which does not comply with PS 1-83 in certainrespects. A label similar to one of these should befound on each sheet of wood panel used.

SPECIAL NOTE: NRCA is concerned regardingpotential fastener holding problems where orientedstrand board and waferboard products are used asthe roof deck component. Please refer to the roof-ing manufacturers' specifICations for acceptable roofdeck materials.

The Span Rating (32/16 in these labels) is of partic-ular significance. The left-hand number of the SpanRating (32 in these labels) indicates the maximumrecommended center-to-center spacing of supportsin inches when the panel is used for roof deckingwith the long dimension of the panel running acrossthe supports. The right-hand number of the SpanRating (16 in these labels) indicates the maximumrecommended spacing of supports in inches whenthe panel is used for subflooring in double-layer con-struction with the long dimension of the panel run-ning across the supports. Therefore, the Span Rat-ing of 32/16 in these labels mean that a particularwood panel may be used either for roof decking oversupports that are spaced 32 inches on center or forsubflooring over supports that are spaced 16 incheson center. In all cases, panels are assumed continu-ous over two or more spans.

XIX. ROOF MEMBRANES

Each built-up roof system is designed to satisfy a specificset of conditions for substrate, life span, roof slope andclimate. The designer should relate these conditions tofield conditions in order to determine the proper specifi-cations. The geographical location and climatic condi-tions to be encountered frequently determine the typeof membrane to be installed. A roof membrane in Arizo-na, where there is little rainfall and extreme sunlight, mayrequire a different roof system than one in Montana, withits extreme temperature variances.

Note: Though the industry termin04ogy refers to ply-

2928

. The rate of speed at which the bitumen is applied(when mechanical application procedures areused)

The application of interply bitumens at excessive ratesis discouraged. (See Section XXIV, Sampling and TestCuts.) Bitumen is used as an adhesive as well as a water-proofing layer, and a thin, complete layer of bitumen isrequired for the installation of felts. Brooming of glassfiber felts may be necessary when using a felt layer orin windy conditions. Brooming should not be requiredwhen using glass fiber felts so long as uniform bleedthrough of bitumen and envelopment of glass fibers oc-curs during application. Brooming of organic felts isrecommended regardless of application method. Whenpossible, all plies should be installed in shingle fashion.Any irregularities, such as fish mouths or blisters, shouldbe repaired prior to the application of surfacing. Mem-branes should be laid as continuously as possible. It isimportant that edge nailers, curbs and penetrations bein place before roofing. On low-sloped roofs, the roofmembranes should be applied perpendicular to the flowof water, beginning at low points in the deck. On slopesover 2 inches per foot, consideration may be given tolaying the felts parallel to the slope.

In the past designers have lacked sufficient engineer-ing data for existing and proposed membranes. Studies,however, have provided much needed technical infor-mation for use in selecting roof membranes. In 1967, theNational Bureau of Standards issued Building ScienceSeries #9, "Thermal Shock Resistance for Built-Up Mem-branes." This study proposed the development of a'strength' factor for membranes, rating their resistanceto thermally induced loads. In 1974, Building Science Ser-ies #55, "Preliminary Performance Criteria for Bitumin-ous Membrane Roofing," proposed performance criteriafor built-up membranes and selected the following per-formance attributes desirable in a good roof membrane:

-Tensile strength -Ply adhesion- Thermal expansion - Abrasion resistance-Flexural strength -Tear resistance-Tensile fatigue strength -Pliability- Flexural fatigue strength - Permeability- Shear strength - Moisture expansion

(punching) - Weather resistance-Impact resistance - Uplift resistance-Notch tensile strength -Fire resistance- Moisture effects on - Fungus attack

strength resistance-Creep

For asphalt roofs, treated wood nailers are required oninclines exceeding 2 inches per foot to help secure in-sulation and roof membranes to non-nailable decks orto decks with insulation. These nailers should be thesame thickness as the insulation and should be installedperpendicular to the slope (on 20-foot centers for slopesup to 3 inches per foot and on 4-foot centers for slopesgreater than 3 inches per foot). This method dictates thatroofing felts be installed parallel to the slope and back-nailed into the wood nailers. (See Backnailing in theGlossary.) Spacing of the wood nailers should not ex-ceed the recommendations of the roof insulationmanufacturer or the roof membrane manufacturer.

While some disagreement exists as to the priority andacceptability of these attributes, the designer is urgedto study the National Bureau of Standards documentsto better understand their relationship to the membraneselection process.

After the built-up roof membrane has been applied, theroofing contractor should advise the general contractoror owner to provide surveilance and protection of the roofduring the remainder of the construction period. Damage

Roofing felts should be laid in bitumen whose tempera-ture falls within the correct application EVT temperaturerange. (See Section XX, Bitumens.) The rates of inter-ply bitumen application will vary according to:

. A particular mopping asphalt's EVT temperaturerange (and its corresponding viscosity range)

. The weights of the rolls

. The ambient temperature and wind chill factors

. The type of felt material to be used

30 31

to the roof membrane by other trades during this periodis a major cause of roof problems. On gravel-surfacedroofs, damage is most difficult to discover and can re-main undetected for years.

Bitumens can be heated at high temperatures forshort periods of time without damage. In fact, theymust be heated to high temperatures in order to achievecomplete fusion and strong bonding of the plies.

The roofing contractor should make a final inspectionof the roof, and, if he finds evidence of so-called "work-bench" abuse, he should prepare a written report to thegeneral contractor and/or owner of any visible damagefound in the roof system. Where damage can be ex-pected, the use of a temporary roof should be con-sidered. (See Section III, Temporary Roofs.)

Temperature affects the viscosity, or flow, of the bitu-men and, thus, the mopping weight. Temperatures thatare too high (bitumen that has low viscosity and highflow) can lead to light moppings, incomplete film cover-age, voids and a potential lack of waterproofing quali-ties. Temperatures that are too low (bitumen that hashigh viscosity and insufficient flow) can lead to heavymappings, which result in poor adhesion, potential slip-page problems, high expansion properties and low ten-sile strengths, which can contribute to roof splits. Obvi-ously, there is an optimum viscosity range, and there-fore, an optimum temperature range at the point of ap-plication for achieving complete fusion, optimum wet-ting and mopping properties, and which results in thedesirable interply bitumen weight.

xx. BITUMENS

Asphalt and coal tar are the bitumens used for roofingpurposes. They are versatile waterproofing materialswhose properties are desirable for use in built-up roof-ing practice. They are thermoplastic, becoming morefluid with heat and reverting to a more solid material asthey cool.

In 1977, the National Roofing Contractors Association(NRCA) adopted the Equiviscous Temperature (EVT)concept. This followed the determination that the flowcharacteristic (viscosity) of roofing bitumens at the pointof application to the substrate is an important factor inthe construction of built-up roof membranes. TheEquiviscous Temperature (EVT) was then defined asthe temperature at which the viscosity of roofingasphalt is 125 centistokes. A centistoke is a unit of aliquid's Kinematic Viscosity. It is obtained by dividing aliquid's dynamic viscosity expressed in centipoise by itsdensity. Subsequently, NRCA redefined the EquiviscousTemperature (EVT) range of roofing asphalt as the tem-perature at which a viscosity of 125 centistokes is at-tained. plus or minus 25 F.

Roofing bitumens are not the "glue" with which roofingfelts are cemented together. Actually, the process ismore of a "welding" or "fusion" process than a glueingprocess. The heated mopping bitumen melts and fuseswith the saturant bitumen in the roofing felts, creatinga "welding" together of the plies. Correct applicationtemperatures are thus vital to the creation of a highoqualityroof membrane system, and a high bitumen temperaturemust be maintained to create the welding process.

The properties of bitumen are such that heating it at hightemperatures for long periods of time may reduce thesoftening point of asphalt and raise the softening pointof coal tar. The property of bitumen has produced thefalse impression that the temperatures ordinarily em-ployed in bituminous heating are damaging to the materi-al. In the past this impression has led to restrictive heat-ing criteria. These restrictions have substantially con-tributed to poor roof installations.

The results of two recent research programs suggest anappropriate Equiviscous Temperature (EVT) for coal tarproducts and a need for modification of the EquiviscousTemperature (EVT) for roofing asphalt.

NRCA recommends the following modifications in defin-ing Equiviscous Temperatures (EVT) for roofing bitumens:

32 33

. Equiviscous Temperature (EVT). The recom-mended temperature for the application of roof-ing bitumens at the mop bucket or felt layer im-mediately prior to application to the substrate.

. Asphalt Products. The recommended Equivis-cous Temperature (EVT) range for roofing asphalt(ASTM 0-312, Type I, II, III, and IV) is the tem-perature at which a viscosity of 75 centipoise isattained, plus or minus 25 F.

. Coal Tar Products. The recommended Equivis-cous Temperature (EVT) range for coal tarproducts (ASTM D-450, Type I and III) is the tem-perature at which a viscosity of 25 centipoise isattained, plus or minus 25 F.

ty of the product. Further, excessive heating may presenta serious flash or fire hazard to property and personnel.In light of these parameters, NRCA makes the followingrecommendations:

. DO maintain kettle and tanker temperature lessthan 25 F below the actual flash point of thematerial used.

. NEVER heat materials to or above the actualflash point.

. DO NOT maintain materials at high temperaturesfor prolonged periods of time.

. DO NOT allow materials to stand in luggers for

long periods.. DO insulate hot transport lines.

. DO circulate materials.

One consequence of a change in EVT from 125 centi-stokes to 75 centipoise, plus or minus 25 F., is the poten-tial need to increase the temperature at which the bitu-men is heated in the kettle or tanker. NRCA encouragesmanufacturers to furnish bitumens with a sufficiently highflash point such that contractors can heat the materialto temperatures sufficient to apply material in the EVTrange, particularly in cold weather applications, withoutmaintaining the material above 25 F. below the actualflash point.

In the event EVT information is not furnished by themanufacturer, the following maximum heating temper-atures for asphalt should be used as guidelines.

NRCA strongly recommends that the following informa-tion be printed on each carton, package and bill of lad-ing for both asphalt and coal tar products:

. Product Type. The type of product by ASTMdesignation, e.g., ASTM D-312, Type III, ASTM0-450, Types I and III.

. Flash Point. The flash point as determined byASTM Standard D-92, Flash and Fire Point byCleveland Open Cup.

. Equiviscous Temperature (EVT) of Asphalt.The temperature at which the asphalt attains aviscosity of 75 centipoise as determined by ASTMMethod 0-4402, Viscosity Determinations of Un-filled Asphalt Using the Brookfield Thermosel

Apparatus.. Equiviscous Temperature (EVT) of Coal Tar.

The temperature at which the coal tar product at-tains a viscosity of 25 centipoise when determinedby ASTM Method 0-4402, Viscosity Determina-tions of Unfilled Asphalt Using the BrookfieldThermosel Apparatus.

Recommendations:Excessive and prolonged heating of asphaltic and coaltar products may have a deleterious effect on the quali-

3534

The most vulnerable part of any roof system is that pointat which the horizontal roof deck and a vertical surfacejoin. Most roof leaks occur at these flashing locations.The designers should carefully consider the design offlashing details at these locations. (See NRCA Construc-tion Details in the NRCA Roofing and WaterproofingManua/.)

The term flashing can be divided into two groups:

1. Composition Flashing (Base Flashing)The bending radius of present composition roofingmaterials is generally limited to 45 degrees. To al-low for this bending radius, all vertical surfaces musthave cant strips installed between the roof and thevertical surface. The height of the base flashingshould be not lower than (a nominal) 8 inches andnot higher than (a nominal) 14 inches above thefinished roof surface. Walls requiring flashingshigher than 14 inches should receive specialmoisture-proofing. A wood nailer strip or suitable de-tail allowing mechanical fastening of the base flash-ing at the top must be provided. Masonry surfacesshould be primed with asphalt concrete primer.

Coal-tar roofing products are described by ASTM Stan-dard 0-450, Types I & III, "Coal Tar Pitch Used in Roof-ing, Dampproofing and Waterproofing." Types I & "' aresuitable for use in the construction of coal tar built-uproofing, the difference being that Type III has less vola-tile components than Type I. The Equiviscous Temper-ature (EVT) concept is equaJly applicable to coal tarproducts, although the recommended viscosity base isconsiderabfy lower for the coal tar products than for roof-ing asphalts. In the event the information is not furnishedby the supplier, the following temperature ranges appearto be appropriate for coal tar for ~h mechanicaJ spread-er and mopping application techniques:

. Coal Tar Pitch (Type I) approximately 360 F plusor minus 25 F

. Coal Tar Bitumen (Type III) approximately 375 Fplus or minus 25 F

XXI. WATER CUTOFFS ANDWEATHER PROTECTION

Water cutoffs are temporary felt courses that are installedto prevent moisture from entering the insulation andmembrane during construction. They should be appliedat the end of each day's work and whenever work is halt-ed for an indefinite period to protect the membrane fromprecipitation. They must be removed prior to installingadditional insulation.

Expansion joint flashings (allowing expansion andcontraction) should be constructed as detailed in theNRCA Construction Details. The wood curbingshould be placed against the wall and secured onlyto the deck. The designer is cautioned to considerthat building components are subjected to thermalmovements at different rates and in different direc-tions from the roof membrane. If the roof is to be tiedinto these components, special consideration shouldbe given to the design of that juncture.

Temporary flashings should be installed as weather pro-tection If permanent flashings are not in place. All open-ings in the membrane should be sealed to prevent anymoisture from entering the roof system before complet-ing membrane application.

Specifications requiring gravel installation each day areunrealistic and sometimes detrimental to the quality ofthe completed roof. Where working conditions permit,roofing felts should be "glazed" and sealed at the endof each day's work if final surfacing is not installed.

2. Metal Flashing (Counterflashlng and CapFlashing)Since metals have a high coefficient of expansion.metal flashing must be isolated from the roof mem-

36 37

brane wherever possible to prevent metal move-ments from splitting the membrane. Aashing detailsthat require metal flanges to be sandwiched into theroof membrane should be avoided if possible.

XXIII. SURFACING AND AGGREGATE

Most roof membranes, if not presurfaced, require sometype of wearing surface. This surfacing should be ap-plied as soon as it is practical after the membrane is in-stalled. Gravel, slag, marble chips, etc. are the ag-gregates used for aggregate-surfaced roofs. Asphalt andliquid surface coatings are used on some smooth-surfaced roofs.

For all walls and protections that receive composi-tion base flashing, metal counterflashing should beinstalled in the wall above the base flashing. The de-sign of this detail should be two-piece, allowing in-stallation of the counterflashing after the base flash-ing. Single-piece installations cannot be flashedproperly nor can reroofing and roofing maintenancebe performed without deforming the metal. Sheetmetal should NEVER be used as a base flashing.

Gravel or aggregate surfacing should be set in hot bitu-men, either by a bitumen dispenser or by hand pouring.Gravel placed by machine will result in somewhat light-er surface bitumen poundages in some locations sincethe gravel, as it flows from the gravelling machine, tendsto create a "wave" effect in the hot bitumen as it isplaced.

Metal wall cap flashing is often used to cover the topof a wall in lieu of masonry copings. In most casesthe metal counterflashing is attached to the insideface of the metal wall cap flashing with sheet metalscrews. Hand pouring produces heavier poundages but less uni-

form coverage, but neither method is preferable to theother. Gravel or other aggregate should be fairly round-ed in shape and should contain a minimum of flat, sharpor elongated particles. At the time of application, the ag-gregate should be hard, durable, opaque, surface dryand free of clay, loam, sand or other foreign substances.Storage piles of aggregate should be placed on coatedor gravelled portions of the membrane and not on barefelt. Occasionally, on well-applied roofs, small black glob-ules known as "raspberries" or "blackberries" will formin the roof surface. These are not detrimental to the roofand simply indicate that large quantities of bitumen floodcoat were applied and have bubbled up around the ag-gregate. To avoid excessive aggregate loss, aggregatesurfacing should not be applied to roofs whose slope isgreater than 3 inches per foot.

Gravel stops should be raised above the waterlineby using tapered cants and wood blocking. Whenthis is not possible, the metal flanges for low-profilegravel stops should be set in mastic on top of thecompleted roof membrane and nailed at close inter-vals to the wood nailer. The metal flange should thenbe primed with asphalt primer and felt flashing stripsapplied. Interior drainage is recommended, andedges should be raised whenever possible. A metaledging should NEVER be used as a water dam orwaterstop. The practice of connecting sheet me-tal to the roof membrane should be avoidedwhenever possible. Pipe projections through themembrane require metal flashing or the insertion ofroof jacks into the membrane. Metal flanges shouldbe set in mastic over the completed membrane andprimed and stripped in with flashing strips. Generally, smooth-surfaced coatings should be applied

as soon as possible after the membrane is installed.Some coatings, however, must be applied over a previ-ously applied thin coating of hot asphalt. The manufac-turer's instructions should be consulted to determine ifthis thin coating is required. If it is, that asphalt shouldbe allowed to "age" (or oxidize) for a period of two to four

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weeks, depending upon the amount of sunlight, beforefinal surfacing is applied. Emulsions must be protectedfrom freezing and must not be applied in freezing tem-peratures or when precipitation is occurring or expect-ed. Frozen material must be discarded.

Foot traffic can be highly detrimental in extremely coldor warm temperatures and should be controlled. Walk-ways, if required, should be constructed of 2-inch x4-inch redwood materials, and fasteners for these walk-ways should not extend through the roof membrane. Allsharp edges should be eliminated from these walkways.

Some pad-type composition walkways have exhibited ex-treme degradation in a short period of time. When thesewalkpads are used, a flood coat and aggregate surfac-ing should be applied first, and the walkpad area thenswept clear of loose aggregate. Good practice dictatesthat one piece of the walkpad be spaced no closer than6 inches from an adjacent piece. The walkpad can thenbe set in hot bitumen on top of the surfacing aggregateand, thereby, raised above the plane of the roof.

XXIV. QUALITY ASSURANCE ANDTEST CUTS

4. AttachmentThe roof membrane and/or insulation should be se-cured with the specified number and types offasteners, nails or bitumen.

5. BitumenThe type of bitumen should be checked to insure thatit is the proper type for the specification, roof slopeand climatic conditions. Proper heating tempera-tures should be maintained in the kettle or tankerto insure that the bitumen will be at the EVT at thepoint of application.

6. Bitumen ApplicationBitumen applicators should be well-versed in thespecified bitumen application rates. In addition, ap-plicators should be thoroughly knowledgeable of thevolume capacity of the equipment being used andthe length of runs required to achieve the specifiedbitumen application rates.

7. Plies of FeltThe specified number of plies of felt should be ap-plied in accordance with specification procedures.The lapping sequence of the felt plies should satis-fy specification requirements to achieve completecoverage.

8. Phased ApplicationThe installation of all plies should be completed inthe same day, and the plies should be surfacedeither with a glaze coat or complete surfacing on allorganic roof membranes. The final surfacing can bedelayed on glass fiber roof membranes.

9. FlashingsComposition base flashings should be completed ona daily basis. Any metal or masonry surfaces wherebitumen materials are to be attached must be primedand allowed to dry. Composition and metal materi-als must be properly secured with appropriatemechanical fasteners using the spacing required(sheet metal 3 inches on center, masonry 6 incheson center, wood 9 inches on center). Walls, projec-tions, wood nailers and other termination pointsshould be completed before roof membrane andflashings are commenced. All sheet metal flashings,

NRCA believes that the most effective method of verify-ing correct roof application is visual inspection duringthe application process by persons experienced andknowledgeable in roofing. To help obtain a high-qualityroof application, the following items should be verified.

1 . Deck SurfaceThe deck surface should be clean, firm, smooth, visi-bly dry and properly secured against movement.

2. MaterialsRoofing materials used on the job should complywith material specifications for the job. All materialsshould be clean, visibly dry and undamaged.

3. Storage of MaterialsRoofing materials should be stored and protected.

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measured and weighed, the results calculated andan evaluation made of the continuity of interply bit-umen. The test cut panel should then be put backin place and readhered, and additional plies, equalto the original specification, should be applied overthe panel location before proceeding to install sur-facing materials.

such as pipe collars, drains, gravel stops, etc. shouldbe on site before roofing is required to be com-menced. No condition should be allowed that wouldpermit moisture entering behind, around or underroof or flashing membrane. Flashing installationsshould be monitored for lap openings and voids.

ASTM D-2829, "Standard Practice for Sampling andAnalysis of Built-Up Roofs," should not be used asa technique to evaluate workmanship. While thismethod is intended for determining the approximatequantities of the components of the sample taken,the precision and accuracy of the analytical methodsdescribed in the ASTM 0-2829 have not been es-tablished by round-robin testing among severallaboratories or by comparative testing of replicateuniform samples within anyone laboratory and thereproducibility among several laboratories of testresults using ASTM D-2829 or other laboratoryprocedures is unknown. Given the lack of knowledgeregarding the precision and accuracy of laboratoryanalysis of roof samples made in accordance withASTM D-2829, the value of drawing conclusions con-cerning the quality and watertight integrity of a roofmembrane on the basis of such test results is high-ly questionable.

10. Gravel AdhesionThe gravel that makes initial contact with the hot bit-umen flood coat should become embedded in thebitumen, leaving the balance of the gravel to serveas ballast and protection for the roof membrane

system.

11. Test CutsTest cuts are occasionally called for in contract docu-ments or are requested by a building owner or con-sultant during roof construction. A thorough, continu-ous visual inspection by a knowledgeable personduring application is far preferable to test cuts as ameans to monitor roof application. Continuous visualinspection during the application provides a far morecomplete, realistic and meaningful means of examin-ing workmanship practices than do test cuts. Roofcuts are an unrealistic basis for drawing conclusionsabout an entire roof and do not address many of thefactors that are critical ot obtaining watertight integri-ty (e.g., flashing, penetrations, drainage, secure-ment, roof-mounted equipment, etc.). Focusing onroof cuts tends to give undue emphasis to the weightof interply bitumen, even though the actual interplybitumen weight is not the controlling factor in obtain-

ing a watertight installation.

XXV. REROOFING

Each reroof or recover project has its own specificproblems that require individual assessment. Thedesigner can obtain much of the information needed toprepare for reroofing by a thorough study of the exist-ing roof system and the reasons for deterioration.

When test cuts are required by job specifications.a minimum of three random samples for the roofarea applied that day should be taken each day pri-or to the installation of surfacing material. Samplingshould be done in accordance with ASTM 03617-83,"Standard Practice for Sampling and Analysis ofNew Built-Up Roof Membranes." This ASTM metho-dology calls for an on-site field evaluation before sur-facing bitumen and aggregate are applied. When atest cut is made, the cut should immediately be

The existing roof deck must be sound and undamaged.A sample of the existing membrane should always beremoved down to the deck. The insulation should becarefully examined. Wet or damaged insulation. in mostcases, should be replaced. It may be possible to salvageexisting roof insulation if it is undamaged or if it is dry.

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Some insulation products cannot be salvaged, t.ecauseremoving the membrane causes delamination of the in-sulation boards. If there is doubt about the adequacy ofthe attachment of the first insulation layer, this layershould be mechanically attached before the attachmentof the seoond layer. Where removing the membrane maycause minor surface damage to the existing insulation,a single minimum layer or recover board should be con-sidered over the existing insulation to provide a suita-ble surface for the new membrane. In addition, thedesigner should carefully calculate the dew-point loca-tion and make provisions for it in his reroofing plans. Thepractice of installing a new roof membrane directly to theexisting roof is discouraged.

Owner Inspection and Maintenance Recommenda-tions

1. Inspect the roof at least twice yearly, in the springand fall, and inspect all roofs after any severe storm.Make frequent inspections on buildings that housemanufacturing facilities that evacuate exhaust debrison to the roof. Clean roof drains of debris. Removeleaves, twigs, cans, balls, etc. which could plug roofdrains. Bag and remove all debris from the roof sincedebris on the roof surface will be quickly swept intodrains by heavy rains, and drainage problems mayoccur.

2. Notify the roofing contractor immediately after a roofleak occurs. If possible, note conditions resulting inleakage. Heavy or light rain, wind direction, temper-ature and the time of year that the leak occurs areall important clues to tracing roof leaks. Notewhether the leaks stop shortly after each rain or con-tinue to drip until the roof is dry. If the owner is pre-pared with facts, the diagnosis and repair of roofproblems can proceed more rapidly.

3. File all job records, plans and specifications for fu-ture reference. Set up a maintenance schedule.Record maintenance procedures as they occur. Logall access times and parties working on the roof incase damage should occur.

4. Do not allow foot traffic on the roof in very cold orvery hot weather; damage can result. Do not allowthe installation of television and radio antennas ormechanical equipment without notifying the roofingcontractor and consulting with him about themethods and details for these installations. One ofthe keys to avoiding roof damage is the key to thepadlock on the roof hatch! Allow only authorized per-sonnel on the roof.

. In emergency situations, patch leaks to minimizeproperty loss.

Except for emergency situations, do not attemptowner-performed roof repairs. The puncturing of ablister or the spreading of a coating or mastic onlycovers up evidence the roofing contractor needs to

Building owners may wish to consider the use of addi-tional insulation in order to anticipate future energy re-quirements. In selecting a new membrane specification,the designer should consider the performance of the oldroof specifications. Changes in the wood-blockingheights and additional expansion provisions may be re-quired at the time of reroofing. The existing drainage pro-visions should be examined and revised as needed.

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Sample evaluation cuts are used to investigate existingroofs. In the hands of skilled investigators, they may helpto identify the nature of the existing roof system. It mustbe stressed that the cuts' usefulness is directly relatedto the experience and expertise of the investigator.

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XXVI. INSPECTION AND MAINTENANCE

All roofs require periodic maintenance for long life.While complex repairs and some maintenance shouldbe performed by qualified roofers. the owner can helpmaintain the roof by seeing that regular clean-up proce-dures are performed. The designer and roofing contrac-tor should make the owner aware of these proceduresafter the roof is completed.

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6

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XXVIII. TO THE OWNER AND DESIGNERascertain the problem. Do not consider using main-tenance coatings, resaturants, sprays or "miracle"products without consulting a qualified roofingcontractor.

Roofing Contractor Maintenance Recommendations

After completion, each roof is subjected to variousweathering conditions. Roofs do not wear uniformly be-cause certain areas may be affected more severely thanothers. Equalizing wear by upgrading worn areas is thesecret to prolonged roof life. To equalize wear theseareas should be maintained and repaired by a qualifiedroofing contractor. Maintenance may be as simple asregravelling a windswept comer, or more complex, suchas correcting a water-ponding problem. But maintenanceis a necessary part of good roofing practice.

XXVII. FACTORY MUTUAL (FM) ANDUNDERWRITERS LABORATORIES (UL)

Insurance bureaus rely on FM and UL requirements forinsurance rating purposes. These requirements havehad a strong impact on the construction of quality roofsystems. They were established to reduce physicaldamage to roofing materials and the ensuing financiallosses. The requirements, however, are aimed atpreventing material waste and financial loss and do notnecessarily guarantee the construction of high-qualityroof systems. Roof components are tested for lossprevention but are NOT tested for the overall perfor-mance of the roof system that is desired. In summary,the use of FM and UL classified materials or methodswill not necessarily result in quality roof systems.

The successful performance of a built-up roof requires:

1 . Proper DesignCompatible materials and systems that will withstandthe environmental conditions of the area where thebuilding is constructed should be carefully selected.The roof system components. as they relate to eachother, should be carefully detailed. While primaryresponsibility for proper design is placed with thedesigner. the roofing contractor and the materialmanufacturer may be consulted for input helpful tothe design.

2. Quality MaterialsMaterial selection should be based on the quality ofthe roof system rather than on economicconsiderations.

3. Quality WorkmanshipOnly skilled. trained workmen familiar with theproducts to be used should perform the work. Inter-ference from other parties involved in the construc-tion process should be avoided.

4. Weather ConsiderationsThe permanent roof system should be constructedunder reasonable weather conditions.

5. Timely MaintenanceDamage to the roof by other trades or by owner per-sonnel should be prevented. The roof should bemaintained in top condition by equalizing wear andby reducing degradation factors with periodic inspec-tions and repairs. A good maintenance program isthe owner's greatest assurance of value.

6. Qualified Roofing ContractorsWork with qualified roofing contractors! Consultthem before issuing plans and specifications. Besure that all contractors are bidding on exactly thesame application procedures and materials.

Some FM and UL requirements change every year. Itis good practice to consult current issues of FM and ULbulletins for the latest information on installation methodsand approved materials on specific building projects.This document will exclude specific FM and UL informa-tion. For further information see the FM and UL sectionof the NRCA Roofing and Waterproofing Manual.

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GLOSSARY Special Steep Asphalt:a roofing asphalt conforming to the requirements ofASTM Specification 0312, Type IV.

Aggregate:(1) crushed stone, crushed slag or water worn gravelused for surfacing a built-up roof; (2) any granular mineralmaterial.

Asphalt, Air Blown:an asphalt produced by blowing air through moltenasphalt at an elevated temperature to raise its soften-ing point and modify other properties.

Alligatortng:the cracking of the surfacing bitumen on a built-up roof,producing a pattern of cracks similar to an alligator'shide; the cracks mayor may not extend through the sur-facing bitumen.

Asphalt Felt:an asphalt-saturated felt or an asphalt coated felt

Asphalt Mastic:a mixture of asphaltic material and graded mineral ag-gregate that can be poured when heated but requiresmechanical manipulation to apply when cool.

Application Rate:the quantity (mass, volume or thickness) of material ap-plied per unit area.

Asphalt, Steam Blown:an asphalt produced by blowing steam through moltenasphalt to modify its properties.

Area Divider:a raised, double wood member attached to a properlyflashed wood base plate that is anchored to the roofdeck. It is used to relieve thermal stresses in a roof sys-tem where no expansion joints have been provided. (SeeNRCA Construction Details.)

ASph8hene:a high molecular weight hydrocarbon fraction precipitat-ed from asphalt by a designated paraffinic naphtha sol-vent at a specified temperature and Uvent-asphaJt ratio.

Asbestos:a group of natural, fibrous, impure silicate materials. NOTE- The asphaltene fraction should be identified by

the temperature and solvent asphalt ratio used.Asphalt:a dark brown to black cementitious material in which thepredominating constituents are bitumens, which occurin nature or are obtained in petroleum processing.

Backnaillng:the practice of blind-nailing roofing felts to a substratein addition to hot-mopping to prevent slippage. (See BlindNailing.)

Dead-Level Asphalt:a roofing asphalt conforming to the requirements ofASTM Specification 0312, Type I.

Base Flashing:(See Flashing.)

Flat Asphalt:a roofing asphalt conforming to the requirements ofASTM Specification 0312. Type II.

Base Ply:the lowenTK)St ply of roofing material in a roof membraneassembly.

Steep Asphalt:a roofing asphalt conforming to the requirements ofASTM Specification D312, Type III.

Base Sheet:a saturated or coated felt placed as the first ply in somemulti-ply built-up roof membranes.

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Bitumen:(1) a class of amorphous, black or dark colored, (solid,semi-solid or viscous) cementitious substances, naturalor manufactured, composed principally of high molecu-lar weight hydrocarbons, soluble in carbon disulfide, andfound in asphalts, tars, pitches and asphaltites; (2) ageneric term used to denote any material composed prin-cipally of bitumen.

Bond:the adhesive and cohesive forces holding two roofingcomponents in intimate contact.

Brooming:embedding a ply of roofing material by using a broomto smooth out the ply and ensure contact with the adhe-sive under the ply.

Bituminous:containing or treated with bitumen. Examples:bituminous concrete, bituminous felts and fabrics,bituminous pavement.

British Thermal Unit (Btu):the heat energy required to raise the temperature of 1pound of water 1 degree Fahrenheit.

Built-Up Roof Membrane:a continuous. semi-flexible roof membrane assembly.consisting of plies of saturated felts. coated felts. fabricsor mats between which alternate layers of bitumen areapplied, generally surfaced with mineral aggregate.bituminous materials. or a granule-surfaced roofingsheet. (Abbreviation: BUR.)

Bituminous Emulsion:(1) a suspension of minute globules of bituminous materi-al in water or in an aqueous solution; (2) a suspensionof minute globules of water or an aqueous solution ina liquid bituminous material (invert emulsion).

Bituminous Grout:a mixture of bituminous material and fine sand that willflow into place without mechanical manipulation whenheated.

Cant Strip:a beveled strip used under flashing to modify the angleat the point where the roofing or waterproofing mem-brane meets any vertical element.

Blackberry:a small bubble or blister in the flood coating of a gravel-surfaced roof membrane.

Cap Flashing:(See Flashing.)

Blind Nailing:the practice of nailing the back portion of a roofing plyin a manner that the fasteners are not exposed to theweather in the finished product.

Capillarity:the action by which the surface of a liquid (where it isin contact with a solid) is elevated or depressed, depend-ing upon the relative attraction of the molecules of theliquid for each other and for those of the solid.

Blister:an enclosed pocket of air mixed with water or solventvapor, trapped between impermeable layers of felt, orbetween the felt and substrate.

Cap Sheet:a granule-surfaced coated sheet used as the top ply ofa built-up roof membrane or flashing.

Blocking:wood built into a roofing system above the deck and be-low the membrane and flashing to stiffen the deckaround an opening, act as a stop for insulation, or toserve as a nailer for attachment of the membrane orflashing.

Caulking:a composition of vehicle and pigment, used at ambienttemperatures for filling joints, that remains plastic for anextended time after application.

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Coal Tar:a dark brown to black. semi-solid hydrocarbon obtainedas residue from the partial evaporation or distillation ofcoal tar.

Counterftashing:formed metal or elastomeric sheeting secured on or intoa wall, curb, pipe, rooftop unit or other surface, to coverand protect the upper edge of a base flashing and itsassociated fasteners.

Coal-Tar Pitch:a coal tar used as the waterproofing agent in dead-level or low slope built-up roof membrane, conform-ing to ASTM Specification 0450, Type I. Coal-TarWaterproofing Pitch: a coal tar used as the damp-proofing or waterproofing agent in below-gradestructures, conforming to ASTM Specification 0450,Type II.

Course:(1) the term used for each application of material thatforms the waterproofing system or the flashing; (2) onelayer of a series of materials applied to a surface (i.e.,a five-course wall flashing is composed of three appli-cations of mastic with one ply of felt sandwiched betweeneach layer of mastic).

Coal-Tar Bitumen:a coal tar used as the waterproofing agent in dead-level or low slope built-up roof membrane, conform-ing to ASTM 0450, Type III.

Coverage:the surface area continuously covered by a specificquantity of a particular roofing material.

Crack:a separation or fracture occurring in a roof membraneor roof deck, generally caused by thermal induced stressor substrate movement.

Coal-Tar Felts:a felt that has been saturated with refined coal tar.

Coated Sheet Felt:(1) an asphalt felt that has been coated on both sideswith harder. more viscous asphalt;

Creep:the permanent deformation of a roofing material or roofsystem caused by the movement of the roof membranethat results from continuous thermal stress or loading.(2) a glass fiber felt that has been simultaneously impreg-

nated and coated with asphalt on both sides.Cricket:a relatively small, elevated area of a roof constructed todivert water around a chimney, curb or other projection.

Cold-Processing Roofing:a continuous, semi-flexible roof membrane. consistingof plies of felts. mats or fabrics that are laminated on aroof with alternate layers of cold-applied roof cement andsurfaced with a cold-applied coating.

Cutback:solvent-thinned bitumen used in cold process roofingadhesives. flashing cements and roof coatings.

Condensation:the conversion of water vapor or other gas to liquid asthe temperature drops or the atmospheric pressure rises.(See Dew-Point.)

Cutoff:a detail designed to prevent lateral water movement intothe insulation where the membrane terminates at the endof a day's work, or used to isolate sections of the roof-ing system. It is usually removed before the continua-tion of the work.

Coping:the covering piece on top of a wall exposed to theweather, usually sloped to shed water.

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Dampproofing:treatment of a surface or structure to resist the passageof water in the absence of hydrostatic pressure.

Edge Stripping:application of felt strips cut to narrower widths than thenormal felt roll width to cover a joint between flashingand built-up roofing.

Dead Level:absolutely horizontal, or zero slope. (See Slope.) Edge Venting:

the practice of providing regularly spaced protectedopening along a roof perimeter to relieve moisture vaporpressure.

Dead-Level Asphalt:(See Asphalt.)

Dead Loads:non-moving rooftop loads, such as mechanical equip-ment, air conditioning units, and the roof deck itself.

Elastomer:a macromolecular material that returns rapidly to its ap-proximate initial dimensions and shape after substan-tial deformation by a weak stress and the subsequentrelease of that stress.Deck:

the structural surface to which the roofing or waterproof-ing system (including insulation) is applied. Elastomerlc:

a rubber like synthetic polymer that will stretch whenpulled and will return quickly to its original shape whenreleased.

Delamination:separation of the plies in a roof membrane system orseparation of laminated layers of insulation.

Embedment:(1) the process of pressing a felt, aggregate, fabric, mat,or panel uniformly and completely into hot bitumen oradhesive; (2) the process of pressing granules into coat-ing in the manufacture of factory prepared roofing.

Dew Point:the temperature at which water vapor starts to condensein cooling air at the existing atmospheric pressure andvapor content.

Double-Pour:the process of applying two layers of aggregate and bit-umen to a built-up roof.

Emulsion:the intimate dispersion of an organic material and waterachieved by using a chemical or clay emulsifying agent.

Drain:a device that allows for the flow of water from a roof area.(See NRCA Construction Details.)

Envelope:a continuous membrane edge seal formed at theperimeter and at penetrations by folding the base sheetor ply over the plies above and securing it to the top ofthe membrane. The envelope prevents bitumen seepagefrom the edge of the membrane.

Dropback:a reduction in the softening point of bitumen that occurswhen bitumen is heated in the absence of air. (SeeSoftening Point Drift.) Equilibrium Moisture

(1) the moisture content of a material stabilized at a giventemperature and relative humidity, expressed as percentmoisture by weight; (2) the typical moisture content ofa material in any given geographical area.

Edge Sheets:felt strips that are cut to widths narrower than the stan-dard width of the full felt roll, used to start the felt shin-gling pattern at a roof edge.

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Equlvlscous Temperature (EVT):the temperature at which the viscosity is 75 centipoisefor asphalt and 25 centipoise for coal tar products; therecommended temperature plus or minus 25 F at thetime of application

Felt Layer:a machine used for applying bitumen and built-up roof-ing felts.

Felt Mill Ream:the mass in pounds of 480 square feet of dry, unsatu-rated felt; also termed "point weight".Expansion Joint:

a structural separation between two building elementsthat allows free movement between the elements withoutdamage to the roofing or waterproofing system.

Fine Mineral Surfacing:water-insoluble. inorganic material, more than 50 per-cent of which passes the No. 35 sieve, used on the sur-face of roofing.Exposure:

(1) the traverse dimension of a roofing element not over-lapped by an adjacent element in any roof system. Theexposure of any ply in a membrane may be computedby dividing the felt width minus 2 inches by the numberof shingled plies; thus, the exposure of 36 inch-wide feltin a shingled, four-ply membrane should be 8-1/2 inches;(2) the time during which a portion of a roofing elementis exposed to the weather.

Fishmouth:(1) a half-cylindrical or half-conical opening formed byan edge wrinkle; (2) in shingles, a half-conical openingformed at a cut edge.

Flashing:the system used to seal membrane edges at walls, ex-pansion joints, drains, gravel stops, and other placeswhere the membrane is interrupted or terminated. Baseflashing covers the edge of the membrane. Cap flash-ing or counterflashing shields the upper edges of thebase flashing.

Fabric:a woven cloth of organic or inorganic filaments, threadsor yarns.

Factory Mutual (FM):an organization that classifies roof assemblies for theirfire characteristics and wind uplift resistance for insur-ance companies in the United States.

Flashing Cement:a trowelable mixture of cutback bitumen and mineralstabilizers, including asbestos or other inorganic fibers.

Flat Asphalt:(See Asphalt.)

Factory Square:108 square feet of roofing material.

Fallback:(See Dropback.)

Flood Coat:the top layer of bitumen into which the aggregate isembedded on an aggregate-surfaced built up roof.

Felt:a flexible sheet manufactured by the interlocking of fibersthrough a combination of mechanical work, moisture andheat. Felts are manufactured principally from vegetablefibers (organic felts), asbestos fibers (asbestos felts) orglass fibers (glass fiber felts); other fibers may be presentin each type.

Fluid Applied:an elastomeric material, fluid at ambient temperature,that dries or cures after application to form a continu-ous membrane. Such systems normally do not incor-porate reinforcement.

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Glass Felt:glass fibers bonded into a sheet with resin and suitablefor impregnation in the manufacture of bituminous water-proofing materials, roof membranes, and shingles.

Incline:the slope of a roof expressed either in percent or in thenumber of vertical units of rise per horizontal unit of run.

Inorganic:being or composed of matter other than hydrocarbonsand their derivatives, or matter that is not of plant oranimal origin.

Glass Mat:a thin mat composed of glass fibers with or without abinder.

Glaze Coat:(1) the top layer of asphalt in a smooth surfaced built-uproof assembly; (2) a thin protective coating of bitumenapplied to the lower plies or top ply of a built up roofmembrane when application of additional felts or theflood coat and aggregate surfacing are delayed.

Insulation:(See Thermal Insulation.]

Job-Average Basis:a technique for determining the average dimensions orquantities of materials, by analysis of roof test cuts. Thetechnique requires a minimum of three test cuts per roofarea, plus one cut for each additional 1 0,000 square feetof roof area. Job-average basis is computed by dividingthe sum of all measurements taken by the number ofmeasurements taken. The results would describe thejob-average for the quantity or dimension.

Gravel:course, granular aggregate, with pieces larger than sandgrains, resulting from the natural erosion of rock.

Gravel Spot:a flanged device, frequently metallic, designed to pro-vide a continuous finished edge for roofing material andto prevent loose aggregate from washing off of the roof.

Knot:an imperfection or non-homogeneity in materials usedin fabric construction, the presence of which causes sur-face irregularities.Headlap:

the minimum distance, measured at 90 degrees to theeaves along the face of a shingle or felt, from the upperedge of the shingle or felt to the nearest exposed surface.

Live loads:moving roof installation equipment, wind, snow, ice orrain.

Holiday:an area where a liquid-applied material is missing. Mastic:

(See Flashing Cement or Asphalt Mastic.)"Hot Stuff' or "Hot":the roofer's term for hot bitumen. Membrane:

a flexible or semi-flexible roof covering or waterproofinglayer, whose primary function is the exclusion of water.Hygroscopic:

attracting, absorbing and retaining atmosphericmoisture. Mesh:

the square opening of a sieve.Ice Dam:a mass of ice formed at the transition from a warm toa cold roof surface, frequently formed by refreezing melt-water at the overhang of a steep roof, causing ice andwater to back up under roofing materials.

Metal Flashing:(See Flashing.) Metal flashing is frequently used asthrough-wall flashing, cap flashing, counterflashing orgravel stops.

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Mineral Fiber Felt:a felt with mineral wood as its principal component.

Spot Mopping:a mopping pattern in which hot bitumen is appliedin roughly circular areas, leaving a grid of un-mopped, perpendicular bands on the roof.Mineral Granules:

opaque, natural, or synthetically colored aggregate com-monly used to surface cap sheets, granule-surfacedsheets, and roofing shingles.

Sprinkle Mopping:a random mopping pattern in which heated bitumenbeads are strewn onto the substrate with a brush ormop.Mineral Stabilizer:

a fine, water-insoluble inorganic material, used in a mix-ture with solid or semi-solid bituminous materials. Strip Mopping:

a mopping pattern in which hot bitumen is appliedin parallel bands.Mineral-Surfaced Roofing:

built-up roofing materials whose top ply consists of agranule-surfaced sheet. Neoprene:

a synthetic rubber (polychloroprene) used in liquid-applied and sheet-applied elastomeric roof membranesor flashings.

Minerai-Surfaced Sheet:a felt that is coated on one or both sides with asphaltand surfaced with mineral granules

Nineteen-Inch Selvage:a prepared roofing sheet with a 17-inch granule surfacedexposure and a nongranule-surfaced 19-inch selvageedge. This material is sometimes referred to as SIS oras Wide Selvage Asphalt Roll Roofing Material Surfacedwith Mineral Granules.

Modified Bitumen:are composite sheets consisting of a copolymer modi-fied bitumen often reinforced and sometimes surfacedwith various types of films, foils and mats.

Mole Run:a meandering ridge in a roof membrane not associatedwith insulation or deck joints.

Ninety-Pound:a prepared organic felt roll roofing with a granule sur-faced exposure that has a mass of approximately 90pounds per 100 square feet.Mop-and-Rop:

an application procedure in which roofing elements (in-sulation boards, felt plies, cap sheets, etc.) are initiallyplaced upside down adjacent to their ultimate locations,are coated with adhesive, and are then turned over andapplied to the substrate.

Organic:being or composed of hydrocarbons or their derivatives,or matter of plant or animal origin.

Parapet Wall:that part of any wall entirely above the roof.Mopping:

the application of hot bitumen with a mop or mechani-cal applicator to the substrate or to the felts of a built-uproof membrane.

Perlite:an aggregate used in lightweight insulating concrete andin preformed perlitic insulation boards, formed by heat-ing and expanding siliceous volcanic glass.Solid Mopping:

a continuous mopping of a surface. leaving no un-mapped areas.

60 61

Perm:a unit of water vapor transmission defined as 1 grain ofwater vapor per square foot per hour per inch of mercu-ry pressure difference (1 inch of mercury = 0.49 psi).The formula for perm is:

P = GRAINS OF WATER VAPOR I SQUAREFOOT. HOUR. INCH MERCURY

Point Weight:(See Felt Mill Ream.)

Pond:a roof surface that is incompletely drained.

Positive Drainage:the drainage condition in which consideration has beenmade for all loading deflections of the deck. and addi-tional roof slope has been provided to ensure drainageof the roof area within 48 hours of rainfall.

Permeance:an index of a material's resistance to water vapor trans-mission. (See Perm.)

Primer:a thin, liquid bitumen applied to a surface to improve theadhesion of subsequent applications of bitumen.

Phased Application:the installation of a roof system or water proofing sys-tem during two or more separate time intervals.

Rake:the slope edge of a roof at the first or last rafter.Picture Framing:

a rectangular pattern of ridges in a roof membrane overinsulation or deck joints. Re-covering:

the process of covering an existing roofing system witha new roofing system.Pitch:

(See Coal Tar and Incline.:Re-entrant Comer:an inside corner of a surface, producing stress concen-trations in the roofing or waterproofing membrane.

Pitch Pocket:a flange. open-bottomed. metal container placed aroundcolumns or other roof penetrations that is filled with hotbitumen or flashing cement to seal the joint. The use ofpitch pockets is not recommended by NAGA.

Reglet:a groove in a wall or other surface adjoining a roof sur-face for use in the attachment of counterflashing.

Plastic Cement:(See Flashing Cement.) Reinforced Membrane:

a roofing or waterproofing membrane reinforced withfelts, mats, fabrics or chopped fibers.Plastomeric:

a plastic like polymer consisting of any of various com-plex organic compounds produced by polymerizationwhich are capable of being molded, extruded or cast intovarious shapes or films. Generally they are thermo plas-tic in nature, i.e., they will soften when heated andharden when cooled.

Relative Humidity:the ratio of the weight of moisture in a given volume ofair-vapor mixture to the saturated (maximum) weight ofwater vapor at the same temperature, expressed as apercentage. For example, if the weight of the moist airis 1 pound and if the air could hold 2 pounds of watervapor at a given temperature, the relative humidity (RH)is 50 percent.

Ply:a layer of felt in a built-up roof membrane system. A four-ply membrane system has four plies of felt.

62 63

Screen:an apparatus with circular apertures for separating sizesof materials.

Replacement:the practice of removing an existing roof system andreplacing it with a new roofing system.

Scuttle:a hatch that provides access to the roof from the interi-or of the building.

A8-rooflng:the process of re-covering or replacing an existing roof-ing system. (See Re-covering and Replacement.)

Seal:(1) a narrow closure strip made of bituminous materials;(2) to secure a roof from the entry of moisture.

Ridging:an upward. tenting displacement of a roof membrane fre-quently occurring over insulation joints, deck joints andbase sheet edges.

Sealant:a mixture of polymers, fillers, and pigments used to filland seal joints where moderate movement is expected;it cures to a resilient solid.

Roll Roofing:smooth-surfaced or mineral-surfaced coated felts.

Roof Assembly:an assembly of interacting roof components (includingthe roof deck) designed to weatherproof and, normally,to insulate a building's top surface.

Selvage:an edge or edging that differs from the main part of (1)a fabric. or (2) granule-surfaced roll roofing material.

Selvage Joint:a lapped joint designed for mineral-surfaced cap sheets.The mineral surfacing is omitted over a small portion ofthe longitudinal edge of the sheet below in order to ob-tain better adhesion of the lapped cap sheet surface withthe bituminous adhesive.

Roof Cement:(See Flashing Cement.:

Roofer:the trade name for the workman who applied roofingmaterial.

Shark Fin:an upward-curled felt side lap or end lap.

Roof System:a system of interacting roof components (not includingthe roof deck) designed to weather proof and, normally.to insulate a building's top surface. Shingle:

(1) a small unit of prepared roofing material designed forinstallation with similar units in overlapping rows on in-clines normally exceeding 25 percent; (2) to cover withshingles; (3) to apply any sheet material in overlappingrows like shingles.

Saddle:a small structure that helps channel surface water todrains. frequently located in a valley. and often construct-ed like a small hip roof or like a pyramid with a diamondshape base. (See Cricket.)

Shingling:(1) the procedure of laying parallel felts so that one lon-gitudinal edge of each felt overlaps and the other lon-gitudinal edge underlaps, and adjacent felt. (See Ply.)Normally, felts are shingled on a slope so that the waterflows over rather than against each lap; (2) the applica-tion of shingles to a sloped roof.

Saturated Felt:a felt that has been partially saturated with low soften-ing point bitumen.

6564

Spot Mopping:(See Mopping.)

Sieve:an apparatus with apertures for separating sizes ofmaterial.

Sprinkle Mopping:(See Mopping.)Slag:

a hard, air-cooled aggregate that is left as a residue fromblast furnaces, used as a surfacing aggregate. Spudding:

the process of removing the roofing aggregate and mostof the bituminous top coating by scraping and chipping.Slippage:

relative lateral movement of adjacent components of abuilt-up membrane. It occurs mainly in roofing mem-branes on a slope, sometimes exposing the lower pliesor even the base sheet to the weather.

Square:the term used to describe 100 square feet of roof area.

Slope:(See Incline.

Stack Vent:a vertical outlet in a built-up roof system designed torelieve the pressure exerted by moisture vapor betweenthe roof membrane and the vapor retarder or deck.

Smooth-Surfaced Roof:a built-up roof membrane surfaced with a layer of hot-mopped asphalt, cold-applied asphalt clay emulsion,cold-applied, asphalt cutback, or sometimes with an un-mopped inorganic felt.

Steep Asphalt:(See Asphalt.)

Strip Mopping:(See Mopping.)

Softening Point:the temperature at which bitumen becomes soft enoughto flow, as determined by an arbitrary, closely definedmethod.

Stripping or Strip-Flashing:(1) the technique of sealing a joint between metal andthe built-up roof membrane with one or two plies of feltor fabric and hot-ap~ied or cold-applied bitumen; (2) thetechnique of taping joints between insulation boards ordeck panels.

Softening Point Drift:a change in the softening point of bitumen during storageor application. (See Dropback.)

Solid Mopping:(See Mopping.)

Substrate:the surface upon which the roofing or waterproofingmembrane is applied (i.e., the structural deck orinsulation).

Special Steep Asphalt:(See Asphalt.) Sump:

an intentional depression around a drainSpilt:a membrane tear resulting from tensile strength. Superimposed Loads:

loads that are added to existing loads. For example, alarge stack of insulation boards placed on top of a struc-tural steel deck.

Split Sheet:(See Nineteen-Inch Selvage.)

66 67

Tapered Edge Strip:a tapered insulation strip used to (1) elevate the roof atthe perimeter and at curbs that extend through a roof;(2) provide a gradual transition from one layer of insula-tion to another.

Taping:(See Stripping.)

Thermal Shock:the stress-producing phenomenon resulting from sud-den temperature changes in a roof membrane when, forexample, a rain shower follows brilliant sunshine.

Tar:a brown or black bituminous material, liquid or semi-solidin consistency, in which the predominating constituentsare bitumens obtained as condensates in the process-ing of coal, petroleum, oil-shale, wood, or other organicmaterials.

Through-Wall Flashing:a water-resistant membrane or material assembly ex-tending through a wall and its cavities, positioned todirect water entering the top of the wall to the exterior.Tarred Felt:

(See Coal-Tar Felt.;Tuck Pointing:(1) troweling mortar into a joint after masonry units arelaid; (2) final treatment of joints in cut stonework. Mortaror a putty-like filler is forced into the joint after the stoneis set.

Test Cut:a sample of the roof membrane that is cut from a roofmembrane to: (a) determine the weight of the averageinterply bitumen moppings; (b) diagnose the conditionof the exiting membrane (e.g., to detect leaks or blisters).

Underwriters Laboratories (UL):an organization that classifies roof assemblies for theirfire characteristics and wind uplift resistance.

Thermal Conductance (C):a unit of heat flow that is used for specific thicknessesof material or for materials of combination construction,such as laminated insulation. The formula for thermalconductance is: kc =

Vapor Migration:the movement of water vapor from a region of high vaporpressure to a region of lower vapor pressure.- THICKNESS IN INCHES

Thermal Conductivity (k):the heat energy that will be transmitted by conductionthrough 1 square foot of 1-inch thick homogeneousmaterial in one hour when there is a difference of 1degree Fahrenheit perpendicularly across the two sur-faces of the material. The formula for thermal conduc-tivity is: k = Btu/SQUARE FOOT I INCH I HOUR I

DEGREE FAHRENHEIT

Vapor Retarder:a material designed to restrict the passage of water vaporthrough a roof or wall.

Vent:an opening designed to convey water vapor or other gasfrom inside a building or a building component to the at-mosphere, thereby relieving vapor pressure.

Thermal Insulation:a material applied to reduce the flow of heat.

Vermiculite:an aggregate used in lightweight insulating concrete.formed by the heating and consequent expansion of amicaceous mineral.

68 69

LIGHT-METAL ROOF EDGEWater Cutoff:(See Cutoff.)

Waterproofing:treatment o~ a surface or structure to prevent the pas-sage of water under hydrostatic pressure.

Wythe:a masonry wall, one masonry unit, a minimum of twoinches thick.

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