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Report on MetalRoofing

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Foreword

The purpose of this report is to provide the NRCA membershipfundamental information concerning the present state of metal roofingand the factors that need to be taken into account by a contractorwhen considering the decision to become involved in this area of

roofing.

The report was prepared under the auspices of the NRCA MetalRoofing Committee, chaired by Roger Steyer, Steyer Roofing Company,Warren, Mich. NRCA wishes to thank the Roofing Industry EducationalInstitute (RIEl) for permission to use material previously published inits course manual and also the following companies for photographsused in the report: Roll Former Corporation, FECO EngineeredSystems, Inc., and ESE Machines, Inc. Thanks is also extended to PaulNimtz, P.D.N. Associates, for his contributions to the report.

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December 1990

REPORT ON METAL ROOFING

Contents

History of Metal Roofing 1

The Metal Roofing Market. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1

Entering the Metal Roofing Market 2

Metal Roof Systems, Types, and Categories. . . . . . . . . . . . . . . . . . . .. 5

Advantages and Limitations of Metal Roofing. . . . . . . . . . . . . . . . . . . . 10

Metals, Coatings, and Laminates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Reroofing Considerations for Structural Standing Seam Roofs. . . . . . . 15

Metal Roofing Performance Considerations and Standards. . . . . . . . . . 17

Glossary of Terms 20

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loading capabilities. Preengineered systems are promoted as less ex-pensive than traditional structures. The metal roof is one of the com-ponents responsible for the savings in that the need for the roof deckrequired by other roof systems is eliminated. In addition, a lightweightroof assembly is produced that meets structural framing requirements.Finally, large open-span interiors are possible without major structural

expenditures.The component roof of preengineered metal buildings is commonly

installed by a general contractor rather than a roofing contractor. It isreasoned that, because the building is designed as a system, there shouldbe a single source for its installation. On the other hand, there may besome concern that roof installation is being accomplished by builderswithout the expertise possessed by the specialized roofing contractor.It is possible that details and other fine points of roof design and in-stallation are sometimes compromised under these circumstances.

Architectural roof systems have also gone through a period of rapidgrowth. Because these panel systems are usually formed by roofingcontractors, it is difficult to estimate square footage or dollar volumefigures; contractors do report, however, that metal is becoming a morepopular choice among designers and owners.

There are a number of associations and organizations involved inthe metal roofing industry. The roofing task force of the AmericanIron and Steel Institute, whose goal is to promote the use of metalroofing, represents steel producers and has members from the MetalBuilding Manufacturers Association (MBMA) and the Metal Construc-tion Association (MCA). MBMA represents manufacturers that havetraditionally been involved mainly with preengineered buildings.MBMA members have generally allowed only their network of autho-rized applicators to install their systems; these are typically generalcontractors doing new construction on metal buildings, including theroof. These manufacturers have made an effort to involve roofing con-tractor in specifying and installing metal roofs, particularly in retrofitoperations. The Metal Construction Association represents metal com-ponents manufacturers. MCA members deal with general contractorsbut have a less formal arrangement with them. They will also sellproducts to roofing and sheet metal contractors as well. The SystemsBuilders Association (SBA) consists mainly of general contractors doingmetal roofing on preengineered buildings.

In the mid- to late 1970s, a few metal building dealers began install-ing standing seam metal roofs on retrofit projects because of thedownturn in new construction. This made some manufacturers cons-cious of how large the reroof market really was. In the past decade,the interest in reroofing has spread to metal building manufacturersand component suppliers across the country.

ENTERING THE METAL ROOFING MARKET

Expertise Required

When deciding whether to enter the metal roofing market, roofingcontractors should realize that the installation of metal roof systems isin many respects only marginally related to that of the traditional low-

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slope roofing to which they may be accustomed. Therefore, contractorsstarting from scratch should carefully consider which of the ways tobecome involved in metal roofing is the best for them.

If the contractor has a sheet metal department that has been formingaccessories, he may already have the basic knowledge of both equip-ment and metal-forming techniques needed to fabricate his own metalpanels. It is more likely, however, that familiarity with the installationof gravel stops and copings alone will not be sufficient for entry intothe metal roofing market. In any case, the contractor new to metalroofing may be wise to investigate premanufactured systems, themanufacturers of which can supply training, systems concepts, qualitydetails, and accessories. They also may be able to supply preformedtrim and flashings, which can save on the cost of equipment invest-ment, at least until such time as the decision is made by the contractorwhether to enter the metal roofing market on a permanent basis.Another advantage of using a premanufactured system is that the con-tractor can share responsibility and liability for installation with an es-tablished manufacturer.

It is important to differentiate between a systems manufacturer and acomponent manufacturer. With the former, the contractor locks in toall aspects of installation. With the latter, the contractor had greaterflexibility in the purchase and installation of components; on the otherhand, component manufacturers may not offer the training or warrantysupport available from the system manufacturer. The choice that thecontractor makes is usually determined by his level of expertise, finan-cial capability, and comfort level.

Equipment Required

Should the contractor make the decision to form his own panels, heshould be aware that there is some basic equipment required for botharchitectural and structural systems. This includes equipment designedto cut panels to width and to form the metal into the desired shapes.Cutting metal to width can be performed by either a slitter or a shear.Slitters are less expensive and can cut any length of metal. The shear isfaster and has a precision edge.

Figure 1 Slitter Figure 2 Shear

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A hand brake, press brake, or pan former can be used to form metal.The hand brake is relatively inexpensive and very flexible. The pressbrake is designed for heavier use and eliminates the need to mark themetal prior to bending it. Pan formers are fairly expensive and arelimited in application to just one or two panel profiles. They cannot beused for flashings, however, so it will still be necessary to have a handor press brake. Pan formers are capable of producing a panel profilefaster than the other options and can form panels to whatever length isdesired. Entry into the structural metal roofing market virtually requiresthe use of a pan former because of the increased number of bends inthe panel and the heavier gauges used.

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Figure 3 Hand Brake Figure 4 Press Brake

Figure 5 Pan Former

Another requirement for either structural or architectural installationis mechanical seaming equipment. This can consist of either relativelyinexpensive hand tools or power seamers. Using power seamers can be

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tricky because, if the dimensions of the panel seam are not accurateand consistent, the seamer can mangle the metal.

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Figure 6 Mechanical Seamer

As previously mentioned, manufacturers of pre~anufactured systemsgenerally offer both training and warranties for their products. Contrac-tors electing to manufacture their own systems on site will not havethese benefits. In addition, they will have to tie up a substantialamount of capital in equipment, which mayor may not be offset bylower fabricating costs, depending on the volume of work. For thesereasons, it is recommended that contractors carefully analyze the costsof equipment investment versus anticipated volume of work to seewhether it makes economic sense.

The contractor who forms his own panels assumes responsibility forquality control. This involves concern not only with the pan-formingprocess itself but also with the quality of the metal. It is important touse high-quality metal, particularly when roll forming long panels withcontinuous coil. Metal that is not straight and level can produce distort-ed panels regardless of the equipment used to form it. Because there isa disparity in the quality of the metal on the market today, it is advisa-ble to research the standards of suppliers and their willingness to ac-cept return of defective material.

METAL ROOF SYSTEMS, TYPES, AND CATEGORIES

Metal roofing systems are traditionally divided into two categories, ar-chitectural and structural. They are aimed at distinct segments of themetal market and have substantially different aesthetic and performance

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requirements. It is important that the correct system type be selectedfor each application. The architectural system is likened to the tradi-tional steep shingled roof, in that it is considered a water shedderrather than a water barrier. Structural systems can be compared to andcompete with traditional low-slope roofs because they are designed tobetter resist moisture on low-slope applications. Following are furtherdefinitions of these two generic types of metal roof systems.

Architectural Architectural systems are designed to shed waterrapidly over the surface of the panels. The panelsare usually seamed with a double-interlock method,which performs well on a slope at least 3 in 12inches. For lower slopes, climatic conditions mustbe considered, particularly ice and snow buildup,and sealant should be used in the ribs. Architecturalpanels require solid decking, and a felt underlay-ment is usually recommended. The panels are usual-ly characterized by a flat pan with a 3/4-in. to 11/2-in.-high rib on each side edge. The absence of bendsand massive ribs provides the panels with a cleanappearance but without adequate strength for use instructural systems. Architectural systems are general-ly selected for use when performance and aestheticsare of equal value. They are considered alternativesto shingles, wood shakes, tile, and slate roofs.

The mansard system attempts to imitate the ar-chitectural standing seam or batten seam look. Froma distance, the two systems may be indistinguish-able. There is an important difference, however. Themansard system uses a simpler method for joiningthe panels: the seams are not mechanically inter-locked. Instead, snap-on caps or slip joints are typi-cally used. Although these kinds of seams are easierto use, they are less watertight than the traditionaldouble interlock used in other architectural systems.For this reason, the use of mansard systems shouldgenerally be confined to steeper-slope applicationsand to specialty purposes, such as mansards andscreen walls.

Structural Structural metal systems are designed to resist thepassage of water under hydrostatic pressures. Theyhave the structural capability of spanning joistswithout being supported by a solid deck and do notrequire an underlayment. They can be installed onslopes as low as 1/4 inch per foot. They are regard-ed as an alternative to built-up, modified bitumen,or single-ply roofs. Structural panels get theirstrength from the use of large, high-rib profiles. Forthis reason, they tend to be considered less aestheti-cally pleasing than architectural systems and aregenerally selected for use when performance, ratherthan aesthetics, is primary.

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Metal panel types fall into many categories:

Standing Seam The term standing seam is often used as a genericdescription for a class of metal roof seams, including some that aredescribed below. More properly, the term refers to one of two kinds ofprofiles, or seam types: (1) the vertical leg/flat pan and (2) the trapezoi-dal seam (see figure 7.) The name standing seam derives from the factthat the seams are joined together above the panel flats. The trapezoi-dal standing seam is more commonly associated with structural stand-ing seam panels.

VERTICAL LEG/FLAT PAN SYSTEM TRAPEZOIDAL SYSTEM

FEMAL'.=JI C-=E SEAM F~ tSEALANT SEALANT

Figure 7 Vertical Leg/Flat Pan and Trapezoidal Profiles

Batten Seam The original batten seam consisted of vertical leg panelsplaced between wood batten strips and covered with a cap. Today, manybatten seam panels are constructed entirely of metal. Because they aredesigned to shed water, they are used primarily in architectural applications.

Figure 8 Batten Seams

Flat Seam The flat seam is created with individual panels applied inshingled application. One panel edge is folded back on top of itself;the other panel is folded under, and the two panels are hookedtogether. Again, because flat panels are considered water shedders, theyare more commonly found in architectural installations.

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Figure 12 Shingled Panels

The Standing Seam Roof

As mentioned previously, the term standing seam is widely used torefer to almost any kind of commercial metal roof system, althoughstrictly speaking it only indicates those metal panels that are joinedtogether above the panel flat. Standing seam roofs can be used as ar-chitectural elements to highlight the aesthetic value of a building or asstructural membranes across the top of a building. The seaming processvaries depending on the manufacturer's product. For both the verticalleg/flat pan and trapezoidal profiles, each panel typically has a maleand female profile (see figure 7). There are a variety of seaming, orpanel interlock, methods. Some are formed by mechanical seamers orby hand, such as the crimped (45 degrees), roll formed (180 degrees),double roll formed (two 180 degrees), and roll and lock (see figure 13).Other seam systems do not require mechanical seaming, such as thesnap-on cap and snap-together methods.

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JL__- CRIMPED SEAMS ,/IJ.~\\\\ ___1 ROLL FORMED SEAMS -_J\-

~ ROLL AND LOCK ~LSEAMS ,Jfi- ,I ,

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Figure 13 Varieties of Seams

Architectural standing seam roof systems are usually installed onsteeper slopes with short panel lengths. They often do not have sealantin the standing seam because they are designed to shed water off thepanel at a rapid rate. The use of short panel lengths also limits theamount of thermal movement that will occur. For this reason, thepanels are attached to the decking with a cleat, which consists of a sin-gle piece without designed allowance for movement, although two-piece cleats are available. Cleats are installed two to three feet oncenter, and the panels simply slide back and forth on them. Because ofthe use of two-piece clips and pan formers, architectural panels cannow be formed in long, full-length panels.

Structural standing seam roof systems are installed on low slopes andare designed to be highly water resistant. They can also be used in ar-chitectural applications. They typically have a factory-applied sealant inone of the standing seams to ensure watertightness. The systems com-monly employ glass fiber insulation rolls. Because these become com-pressed at the structural members, spacer blocks are often placed overthe structural member to prevent thermal bridging. Sometimes rigid-board insulation is used instead of glass fiber.

The seaming, or joining together, of the metal panels gives the metalsystem the quality of a single-ply membrane in that it is a free-floatingsurface that expands and contracts with temperature changes. The ther-mal movement of the roof panel is provided by the concealed clipsthat are formed into the standing seams during the seaming operation.These clips are typically of two-piece design and are attached to secon-dary structures at no more than five feet on center. The amount ofthermal movement is a factor of the length of the panel run, the tem-perature changes that the panel will undergo, and the type of materialthat makes up the panel.

ADVANTAGES AND LIMITATIONS OF METAL ROOFING

Among the most commonly claimed advantages of metal roofs is

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Galvanic Series* Magnesium Active

* Zinc* Cadmium

*Aluminum 2017*Steel (plain)

Anodic .Cast iron* Lead

* Tin* Brasses

* Copper* Bronzes

Cathodic * Titanium* Monel

*Nickel (passive)* 304 stainless (passive)

* 316 stainless (passive)* Silver

* Graphite Noble

This is the principle of galvanized sheet steels. The more anodic zinccoating, if penetrated, corrodes preferentially to prevent the morecathodic steel substrate from rusting. Once the zinc coating is nickedor scratched, the steel continues to be protected by galvanic action. Be-cause zinc has good "throwing power," it will actually "heal" a nick inthe coating and provides excellent protection at cut edges and drilledholes. The galvanic deposits, or zinc oxides, that form are water solu-ble. As they weather and wash away, more zinc oxide is formed. Thissacrificial process continues until all the zinc in a localized area is con-sumed. Only then does the base steel begins to rust.

While it remains, the zinc also acts as a barrier between the at-mosphere and the base steel. The duration of the protection offered byzinc is a direct function of the thickness of the coating and the severityof the environment. All things being equal, the thicker the zinc coat-ing, the longer it will protect the base steel.

Coating weights for galvanized sheet vary, but for roofing applica-tions they are typically G90 or, 0.90 oz. of zinc per square foot, totalboth sides. The coating is a little less than one mil thick per side. Gal-vanized steel of equal coating weights will corrode at different rates de-pending upon the environment. Environmental factors include durationand frequency of moisture contact, rate at which the surface dries, sa-line content of the moisture, and the extent of industrial pollution. Themore severe the conditions, the more rapid the loss of zinc.

The galvanic steel chart is also useful for analyzing the interactionsof different metals that may come in contact with one another in thepresence of moisture, in particular the interaction that takes placewhen water run-off from a more noble metal passes over an active me-tal. This explains, for example, why the draining from a copper gutterinto a galvanized downspout will result in premature failure of the

downspout.

Aluminized Steel Aluminized steel was introduced more recently thangalvanized steel as a roofing product. Pioneered in the late 1930s, itwas made commercially available for roofing in 1954. Unlike galvanized

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Lead

Lead is used as a roofing accessory because of its extreme workability..It is designated by weight from one to eight pounds per foot. It can beeasily soldered and has great resistance to atmospheric corrosion.

rente

Terne metal, available in 26, 28, and 30 gauge, consists of copper-bearing steel coated on both sides with a tin-lead alloy. TCS is terne-coated stainless steel; it is noted for corrosion resistance in industrial,chemical, and marine environments. Both products can be soldered.Terne requires a protective coating for field application. TCS weathersto a dark gray color.

Terne metal is not recommended for applications over high-humidityinteriors, because premature rusting may result. Maintenance of paintintegrity is critical to the long-term performance of the product.

Summary

There are other metals available for use in metal roofing that can beselected based on special performance requirements for a roof system.Consideration should also be given to the fact that many of the metalsare available in different tempers and alloys, which may have an effecton the end result.

Paint Systems

There are a wide variety of generic paint -systems available, andmanufacturers have their own formulation for each. Paint systems arecharacterized by performance, measurements of which include: (1) ex-terior durability (fading and chalking resistance), (2) adhesion (howwell it bonds to the substrate), (3) gloss, (4) hardness (scratchresistance), (5) flexibility (formability), and (6) chemical and generalcorrosion resistance (durability).

Because of their overall performance, polyesters, siliconized poly-esters, and fluorocarbons are the most widely used paint systems forstanding seam metal roof application. Polyesters are organic polymersthat are relatively hard and abrasion resistant. Durability varies widelydepending on the specific formulation. Siliconized polyesters are poly-esters modified by the addition of silicon, an inorganic substance. Theypossess enhanced exterior durability because of chalking resistance andgloss retention. Fluorocarbons are substituted ethylene polymers. Theyare premium coatings in terms of performance and price. They featureoutstanding formability, heat resistance, color retention, and resistanceto solvents and chalking.

Polyester, modified polyesters, and fluorocarbons are applied as two-coat systems (prime and finish coat) having a total thickness of aboutone mil on the exposed side and roughly one-half mil on the other.Like aluminized and Galvalume steels, paint systems can be warrantedfor up to 20 years depending on the system and the manufacturer.Paint warranties run concurrently with base steel warranties.

Prior to World War II, paint was usually applied to individual panels

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following roll forming or after installation. Today the paint is appliedin a process known as coil coating, which is the application of an or-ganic finish to a coil of metal. The advantages of coil coating arenumerous, from both a productivity and quality standpoint. Like hotdip metallic coating, coil coating is a continuous process. The head endof each coil is welded to the tail end of the previous one. The continu-ous strip is first cleaned to remove dirt and oil, and then the surface ischemically prepared for painting. A prime coat, about 0.2 mils thick, isapplied and cured under heat. This is followed by a top coat about 0.8mils thick, which is also cured. Wax finishes to facilitate roll formingand strippable films for protection against damage can also be appliedat this point. The coil is rewound, packaged, and shipped to the stand-ing seam roof manufacturer.

Laminates

Laminates are applied as a plastic film rather than a liquid. They arethicker (up to three times) and generally more durable than liquid paintsystems. They can be used with or without a liquid primer, dependingon the metallic coating, and virtually eliminate problems of chalking,fading, chipping, peeling, and other forms of degradation. They arealso more expensive than most paint systems. Acrylic and fluorocarbonfilm laminates are the most common in exterior building applications.Extended warranties are available.

Laminates are also applied on coil coating lines; they are adhesivelybonded to the coil under pressure and, sometimes, heat. The rest ofthe process is similar to coil coating with a liquid system.

In general, paints and laminates are as formable as the metallic coat-ings beneath them. Painted and laminated steel sheets can be sheared,punched, press braked, and roll formed without damage to the coatingif proper techniques and tools are used. But organic finishes are not in-destructible. Care must be taken to avoid damaging the finish instorage, handling, and fabrication, or the result can be a marred surfacethat, if deep enough, can lead to premature corrosion. Damaged areascan be repainted, but the manufacturer should be consulted for the

proper technique.Paint and film laminates can be used to both enhance the appearance

and extend the life of metal roofing systems. The wide range of colorsand the proven performance of these systems has expanded the use ofmetal roofing into architecturally demanding applications.

In the last few years, a number of specialty finishes have been deve-loped to meet particular performance requirements, such as salt waterexposure, high-abrasion resistance, and low-glare characteristics. It is agood idea to discuss any special needs with a paint supplier to deter-mine what is available to meet your needs.

REROOFING CONSIDERATIONS FOR STRUCTURAL STANDINGSEAM ROOFS

To obtain the minimum 1/4-inch-per-foot slope generally required forstructural standing seam systems, some form of light-gauge metal struc-tural members are used, which will vary depending on the manufac-turer. Most metal reroofing systems consist of three basic components:

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panels; secondary structural framing; and flashings, trims, and accesso-ries. Preengineered structural framing systems are not widely available;the majority are standard building components that must be field cut,bolted, or welded to suit the particular needs of a roof, although a fewsystems minimize the field-fit work. Framing systems are composed ofa base or lower support channel, vertical, or inclined adjustable, orprecut members, and a top spanning member to support the roof panelat a predetermined slope (see Figure 14). These secondary structurnlmembers are the key to an economical reroofing solution. The moreflexible ones require less field work and, therefore, are more economi-cal. The spacing of these framing members depends more on the un-derlying structural support location orientation than on the panel'sspan limitation.

BASE PLATE PARALLEL PERPENDICULARCONFIGURATlDN CONFIGURATION CONFIGURATION

T 5'0 FLAT5'0" 5'0. FLAT

Figure 14 Framing Configurations

Proper attachment of the new roof framing members to the existingroof is critical. Systems that use individual mini-columns with baseplates usually must be attached directly over the purlin, bar joists, orbeams. Systems that use continuous base channels can be attached tothe existing metal or to the wood deck.

Trim, flashings, and accessories are very in'.portant in reroofingprojects. Many trims and flashings require fi(:ld fitting to suit a particu-lar condition.

The system chosen should provide for some form of adjustability inthe vertical supports that allow for the variances in the surface of theold roof. Above all, they must be attached to the existing structureproperly with the right type of fasteners.

To ensure the proper pullout values of the fasteners, pullout testsshould be conducted and the values recorded. A simple rule of thumbfor attachment is that a 90 rating, as in UL 90, represents 90 poundsper square feet of uplift force. If a roof panel is 24 inches wide andsupports are on 5-foot centers, the panel clip will be holding down 10square feet, or 900 pounds, of uplift. If the structural members are laidout on a 5-by-5 foot grid, the uplift value becomes 2,250 pounds.

Moisture content in the old roofing assembly is another key area ofconcern. All ponding water and wet insulation must be removed. De-pending upon the condition of the existing roof, ventilation mayor

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may not be necessary through the plenum area. Each manufacturershould have a variety of gable, ridge, soffit, and hood ventilating sys-tems available.

Metal for reroofing is not the answer to all projects. When specified,designed, and installed properly, however, it becomes a permanentroofing solution for a wide range of commercial, institutional, residen-tial, and industrial applications.

METAL ROOFING PERFORMANCE CONSIDERATIONS ANDSTANDARDS

Before discussing performance standards, it should be determinedwhich aspects of a metal roof system are so important that they merit aquantifiable pedormance rating. This way the owner or contractor can~ake the proper decision on which system to use for a particularbuilding. Basic considerations should include the following.

System Watertightness The most important function of a roof is to keepout water. Ideally, complete testing should deal not only with seamsbut also panel laps, flashings, ice and snow considerations, and paneldistortion during wind storms.

Wind Uplift Testing must relate to panels as they are affected byperimeter flashing conditions and panel distortion. Building design andslope are an additional factor in ultimate pedormance.

Loads When the metal roof system is used directly over a structuralframing member without decking underneath, the system must becapable of supporting wind, rain, snow, and traffic.

Fire Resistance Although metals are inherently fire resistant, other com-ponents, such as insulation and coatings, may affect the flammability ofthe system.

Life Expectan'}'/Maintenance Requirements Longevity of a systemtends to defy testing, but there are some system characteristics thathave an effect on the expected life. These include:

Thickness of the Metal While the weathering rates of metalsvary, thicker metal of a given kind will outlast thinner metal ofthe same kind. The difference might be measured in months,years, or decades. On the other hand, there may be no differ-ence if the weathering longevity is dependent on coatings ratherthan the metal itself.

Coatings The use of low-quality paints or coatings can ap-preciably shorten the life of some systems, and paint quality canvary dramatically. Kynar paints, which carry a 20-year warranty,are performing well on installations that have surpassed thisperiod of time. Siliconized polyesters can be expected to per-form well for about eight to twelve years before chalking andfading accelerates. ~

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Sealants Metal roof systems should not depend on sealants, par-ticularly in exposed applications. Remember that a metal roof isconstantly moving, which can cause gaps in the sealant.

Details As much so as with any roof system, detailing will makeor break an installation.

Accessory Components All components of the system should bematched for consistent life expectancy. A fifty-year panel helddown by a five-year clip fastened with a two-year fastener willfail in two years.

Systems Selection A system should b~ selected that is designedfor the needs of your building. Don't use a mansard panel for astructural application. Also, climate is an important considera-tion: what works well in Southern California may fail in moun-tain snow country.

System Sophistication Systems that use lots of exposed fastenersare more likely to leak than concealed fastener systems, despitethe fact that gasketed screws can perform well. A system thatsnaps together easily may give increased design flexibility, but italso likely to result in more maintenance in the form of replac-ing snap-on caps that work loose over time. For buildings withcontinual lengths of metal panels, expansion and contractionmust be allowed for. The use of expansion cleats that providefor this movement are required.

Dew Point Interior moisture and condensation can corrodefasteners, cleats, and panels from within. The dew point mustbe considered and dealt with through the use of insulationand/or vapor retarders.

Concerning test method for metal roofing, the problem that we con-front is that most tests used today were not developed for metal roof-ing exclusively. Therefore they do not take into account somecharacteristics of metal roofs not shared by other systems. The resultcan be test results that are inaccurate or even irrelevant; they are usedfor metal roofs because there are no widely accepted alternatives.

Watertightness The tests commonly used today are ASTM E283, airfiltration, and ASTM E331, water infiltration. They are good indicatorsof the watertightness of a system. They use positive and negative airpressure testing with and without water to determine air leakage ratesand ease of water penetration; however, the tests rely on differential airpressure to draw water through the seam. Heavy rains without windcan yield different relative results. The tests also minimize the effectthat seam height has on the effectiveness of rain being shed off the roof.

uPlift Currently Underwriter Laboratories (UL) has the most widelyused and promoted wind uplift tests in the metal roofing industry. Theseresult in ratings of 1-60 or 1-90. But UL itself states that the test resultsshould not be construed as reflecting real-life performance but merely aquantitative comparison of systems for insurance-rating purposes.

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GLOSSARY OF METAL ROOFING TERMS

Aluminized steel Sheet steel with a thin aluminum coating bondedto the surface to enhance weathering charac-teristics

Aluminum A nonrusting metal sometimes used for metalroofing and flashing

Apron flashing A term used for a flashing located at the junctureof the top of the sloped roof and a vertical wallor steeper-sloped roof

Architectural panel A metal roof panel, typically a double standingseam or batten seam, that usually requires soliddecking underneath and a relatively steep slope

Barrel vault A building profile featuring a rounded profile tothe roof on the short axis, but no angle changeon a cut through along the long axis

Batten A wood strip placed between metal panels towhich the panels are attached

Batten seam A metal panel profile attached to and formedaround a wood batten

Bermuda seam A metal panel profile featuring a step-down pro-file that runs perpendicular to the slope of theroof

Blanket insulation A nonrigid compressible insulation usually packedin rolls

Brackets Adjustable framing, usually metal, temporarily af-fiXed to the roof or wall to provide a work sur-face on unwalkable roof pitches

Brakes Hand- or power-activated machinery used to formmetal

Button punch A process of indenting two or more thicknessesof metal that are pressed against each other toprevent slippage between the metal

Butyl tape A sealant tape sometimes used between metal roofseams and end laps and in other sealant appli-cations

Channel A structural framing member

Chevron A style of metal panel seaming/design

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Cleat A formed metal piece that anchors the metalpanel to the roof deck or structural member

Clip A cleat

Closure A formed metal or foam piece used to preventwind or moisture from entering the building atthe top or bottom of panels between the ribs ofthe panels

Conductor A vertical tube used to carry water from guttersdown to ground level.

Coping A formed metal piece used to cover the top of aparapet

Copper A natural weathering metal used in metal roofing;typically used in 16- or 20-oz.-per-square-footthickness

Cornice The decorative sloped underside of a roofoverhang

Counterflashing A cap flashing

Cover plate A metal strip installed over the joint between twopieces of coping or other formed metal

Dome A roof that is shaped like a half-circle or a varia-tion of one

Double standing A method of interlocking two metal panelsseam together. Panels are seam hooked together and

then folded over each other a second time.

Expansion cleat A cleat designed to handle thermal movement ofthe panels

Fascia A vertical or steeply sloped roof or trim locatedat the perimeter of a building. Typically it is aborder for the low slope roof system that water-proofs the interior portions of the building.

Flat lock A method of interlocking metal panels in whichone panel edge is folded back on top of itself andthe other panel is folded under, after which thetwo panels are hooked together

Factory Mutual An insurance testing agency that rates roofing sys-(FM) terns for different performance characteristics

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Furls A small metal sleeve placed inside a gutter at thetop. A spike is nailed through the gutter into thefascia board to hold the gutter up. The furl holdsthe gutter in its original shape.

Galvalume A steel product with a combination galvanizedand aluminum coating applied to it and a natural-ly weathering grey finish

Galvanic action A reaction between dissimilar metals in contactwith one other that can cause premature wearingthrough one of the metals

Galvanized metal Steel with a galvanized coating; generally paintedin exposed applications for long-life expectancy

Gauge A method of rating metal thickness

Girt A structural framing member

Hem The edge created by folding metal back on itself

1-60 An insurance rating for roof system upliftresistance

1 -90 An insurance rating for roof system upliftresistance

J Trim A metal trim flashing shaped like a ]

Knee cap A metal cover trim that fits over a panel rib afterit has been cut and bent

Lap joint A juncture of two metal lengths where one pieceof metal simply overlaps the second

Lead A soft workable metal used for miscellaneousflashings

Lead-coated Copper sheet with a lead coating applied to it

copper

Load The weight of wind, snow, ice, rain, or foottraffic on the roof

Mansard A decorative sloped roof on the perimeter of a

building

Mansard system A metal roof system with limited watertightnessthat requires a steep slope and a felt underlay-ment for satisfactory waterproofing characteristics

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Miter The point of slope transition

Neoprene A synthetic rubber (polychloroprene) used inliquid-applied and sheet-applied elastomeric roofmembranes or flashings

Pan The bottom flat part of a roofing panel which isbetween the ribs of the panel

Pan former Power roll-fo~ng equipment that produce a me-tal roofing panel from a flat sheet

Perlite An aggregate used in lightweight insulating con-crete and in preformed perlitic insulation boards,formed by heating and expanding siliceous vol-canic glass

Pittsburgh lock A type of interlocking of metal, usually at a slopechange

Pressure bar A heavy gauge metal bar used for terminating aflashing against a wall

Purlin A structural framing member

Ridge cap A metal flashing applied over the metal roof atthe ridge

Rigid insulation Compression-resistant insulation

Roof system A system of interacting roof components (exclud-ing the roof deck) designed to weatherproof and,normally, to insulate a building's top surface

Screen wall A nonstructural wall erected around units orcurbs on a roof. Typically the framing consists ofgirts with a wood or metal covering attached tothe frame.

Seam The interlocking point of two metal panels

Siding Vertical metal panels

Sill flashing A flashing installed at the base of a window, door,and the like

Single standing A standing seam that utilizes one overlapping in-seam terlock between two seam panels, in contrast

with the double interlocking used in a doublestanding seam

Snap-on cap A separate cap that snaps on over the vertical legsof some single standing or batten seam systems

Snow guard A device attached to the roof near the eve to pre-vent sudden snow or ice slides from the roof

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