dr. james l. hoff, dba introduction to low- slope roofing

Dr. James L. Hoff, DBA

INTRODUCTION TO LOW-SLOPE ROOFING

Commercial Roofing

• Historical Perspective• Modern Roofing Materials• Roofing• New Roofing Trends

Historical BackgroundPre-1900: Before the Modern Age

• Roofing materials selected for durability and appearance

• Slate• Tile• Metal

• Roofing systems designed to shed water• Gables• Hips• Valleys• Crowns• Saddles• Gutters• Downspouts

Historical Background1920s : The Bauhaus

• Lightweight Framing Systems• Roof weight becomes a consideration

• Rectangular, Low-Rise Profiles• Roof plane becomes virtually level

• Facades and Parapets• Roof becomes an isolated sump

As a result, roofing materials were selected on the basis of durability and weight, while roof systems were designed to resist water.

What started as architectural theory is now economic fact

“Steeply sloped roofs on the large, sprawling buildings that dominate today’s construction would dramatically cut the costs of re-roofing, repair and litigation. but they would raise construction costs by a far greater amount … the costs of steeply sloped roofs over the vast acreages covered by modern buildings are simply too high a price to pay to avoid the problems posed by low-slope roof systems.”

(C. W. Griffith & R. Fricklas, Manual of Low-Slope Roofing Systems, 1996)

Historical BackgroundToday : The “Big Box”

Historical Background

1840s – 1970s: Built-Up Roofing

• Originally employed to waterproof ships

• Redundant layers of bitumen & felts• Bitumen serves as adhesive and

waterproofing• Felts stabilize and strengthen the bitumen

• Frequently surfaced with aggregate • Traditional “tar & gravel” roof





• Dominated commercial roofing for over a century

• Provided a satisfactory barrier to water entry• Success attributed to redundancy of design

and well-understood application standards


1970s: The Perfect Storm

• Health concerns over asbestos • Asbestos felts replaced by organic (paper) felts

• Lower strength• Higher moisture absorption

• OPEC oil embargo• Cost of asphalt increased dramatically• Quality of asphalt decreased

• Increasing energy efficiency• Higher “R” insulations installed under built-up

membranes• Splitting due to “thermal shock” increased


1980s: New Answers – And Plenty of Them

“According to industry estimates, over 100 new manufacturers of roofing products emerged during the ‘70s and early ‘80s, each offering the ‘miracle’ answer for roofing performance.”

(J.L. Hoff, “The Commercial Roofing Industry: New Directions in Construction Quality”, 2003)

• Tire manufacturers introduce rubber roofingNeoprene, Butyl, EPDM

• Textile manufacturers introduce thermoplastic roofing

PVC, CPE, CSPE, E-P, TPO, HDPE

• Asphalt manufacturers introduce polymer-modified roofing

APP, SBS, SEBS, E-P

• Chemical manufacturers introduce synthetic coatings

Acrylics, Polyurethanes


1990s: Consolidation

• Rubber roofing consolidates around EPDM

• Thermoplastic roofing consolidates around PVC and TPO

• Polymer modification (APP & SBS) integrates into traditional asphalt roofing

• Roof coatings relegated primarily to maintenance applications

U.S. Low-Slope Commercial Roofing Market

Key Market Segments (Millions of Square Feet 2003)

Built-Up Roofing(BUR)17%

Modified Asphalt(APP & SBS)

30%

Thermoplastic(PVC & TPO)

23%

Rubber Roofing(EPDM)

30%

Single-Ply Asphalt

Roofing System Overview

Single-Ply

• THERMOSET•EPDM

• THERMOPLASTIC•PVC •TPO


EPDM

+ Large panel sizes for fast coverage

+ Outstanding resistance to weathering

+ High elongation to accommodate building movement


EPDM: Ballasted System

Simple, economical design provides proven performance Stone ballast provides Class A Fire Rating Compatible with most insulations Large panels provide efficient coverage of large roof areas

Insulation

Deck

Stone Ballast or PaversMembrane


EPDM: Ballasted System


EPDM: Adhered System

AdhesiveAdhesive

Insulation

Deck

Design Flexibility - Adapts easily to unusual roof profiles Excellent for high wind conditions Time-proven application method provides high dependability

Insulation plates &fasteners

Membrane


EPDM: Adhered System


EPDM: Mechanically Attached

Metal Or Polymer Batten

Embedded In Field SeamMembrane

Insulation

Deck

Light weight - adapts to most roof decks Reduced labor input

Seaming Tape


EPDM: Mechanically Attached


Thermoplastic

+ Heat-reflective white surface

+ Fast, simple welded panel seams

+ Available in variety of colors


Thermoplastic Installation


Asphalt

• Built-Up Roofing•BUR

• Modified Bitumen•APP•SBS


Built-Up Roofing (BUR)

Insulation

Cover Board

Ply Felts SetIn Asphalt

Gravel Surfacing



Roofing Felts in Hot Asphalt



Gravel-Surfaced BUR


Modified Bitumen

Insulation

Cover Board

Base Sheet

Cap Sheet


Modified Bitumen

Asphalt Modifiers

APP•Atactic Polypropylene

•Thermoplastic Polymer

•Adds Flexibility

•Excellent High Temp. Strength

•Excellent uV Resistance

SBS•Styrene-Butadiene-Styrene

•Thermoset (Rubber) Polymer

•Adds Flexibility & Memory

•Excellent Low Temp. Flexibility

•Requires uV Resistant

Surfacing


Modified Bitumen

Hot Mopped

Cold Applied

Torch Applied


Modified Bitumen


Modified Bitumen

Roofing System Performance

How Long Do Roofs Last?

System Type

Single-PlyBuilt-Up RoofingModified Bitumen

Average Service Life

16.8 – 18.4 Years13.6 – 18.1 Years17.6 – 18.2 Years

“A documented historical performance of roofing assemblies in the United States: 1975–1996”. K. G. Schneider & A. S. Keenan.. Proceedings of the Fourth International Symposium on Roofing Technology (pp. 132-137). Rosemont, IL: National Roofing Contractors Association, 1997.

“…Life span is defined as the time period from the initial roofing membrane installation through recover/re-roof. Based on the results of the statistical model, the current average low slope roofing life span is estimated to be 17.45 years”

“Comprehensive Nonresidential Building Analysis to Estimate the Current Reality of Roofing Longevity”, Ducker Research, 2003.

Ultraviolet Aging Roof Traffic Chemical Exposure Building Movement Reflectivity Color Options High Production Work Area Limitations

Relative Cost

EPDM+++

+

+++

+++++

1.0 - 1.2

PVC/TPO++

+ (PVC)

+++++++++

1.1 - 1.3

BUR+

+++

++

1.2 - 1.4

Mod Bit+

++

+

++++

+++

1.1 - 1.3


Performance Features


Roof Insulation

One Component

Three Functions

Roofing Insulation

Thermal Barrier

0

1

2

3

4

5

6

7

Polyiso XPS EPS FiberGlass

Perlite FiberBoard

Typical “R” Value per Inch Thickness

Roofing Insulation:

Working Platform

Roofing Insulation:

Drainage Structure


Drainage Issues

Slo

pe

Typical2-WayStructural Slope

Interior Drain (Typ.) Typical2-WayStructural Slope


Drainage Issues

4-WaySlope usingTaperedInsulation


Drainage Solution


New Roofing Trends & Concepts

• Cool Roofs• Green / Garden Roofs• Solar Roofs• Roof Recycling

Cool Roofs:

Saving Energy & Reducing Urban Heat Islands

Peak Cooling Loads Reduced Ambient Air Temperatures

Reduced

Lindberg TerminalSt. Louis , MO

Ice MountainBrea, CA

Cool Membrane Roofs Cool Metal Roofs

How Do You Maintain Surface Reflectivity?

Portland

Boston

New York

Pittsburgh

BaltimoreCleveland

Detroit

Indianapolis

Chicago

Milwaukee

Minneapolis

Richmond

CharlotteNashville

Atlanta

St. Louis

Little Rock

Jacksonville

Miami

TampaNew Orleans

Houston

Ft. Worth

Phoenix

Boulder

Cheyenne

Boise

Reno

Portland

Seattle

SLC

Las VegasLos

Angeles

AlbuquerqueOk. City

Louisville

Birmingham

Kansas City

San Francisco

$0$100$200

$300

$400$500

$0$100

$200

$300$400

$500

(-$50)

(-$100)

(-$50)

Are Cool Roofs Right For All Climates?

Minute Maid StadiumHouston, TX Annual Heating / Cooling Cost Savings:

Reflective Roof versus Non-Reflective Roof(Dollars per 20,000 Sq. Ft. Roof Area / R-20 Insulation)

Cool Roofs:

Current Issues & Concerns

Envelop Systems Research Apparatus

Oak Ridge National Laboratories

New Cool Roof Alternatives: Stone & Paver Ballasted Systems

New Cool Roof Alternatives: Stone & Paver Ballasted Systems

Ballasted roofs can provide the same peak energy savings and reduced air temperatures as “cool” roofs …and their performance doesn’t degrade over time!

Comparative Surface Temperature & Heat Transfer

Black Roof

White Roof

Standard Ballast

Heavy Ballast

Concrete Pavers

Garden / Green Roofs: Saving Energy & Reducing Pollution

Chicago City HallChicago, IL

US Environmental Protection AgencyDenver, CO

Underlying roof system must accommodate increased maintenance traffic

Underlying roof system must be designed to meet or exceed to expected garden service life

Leak detection is difficult

Roof repair and maintenance may be difficult if/when needed

Ambient air temperature reduced

Storm water runoff mitigated

Wide variety of hardy plants available

Require as little as 2 or 3 inches of planting medium

Can be combined with “cool” ballasted roofs to minimize initial costs

Tray systems available to minimize maintenance needs

Benefits: Issues:

Garden / Green Roofs: Benefits & Issues

Solar Roofs: Clean Energy Production

Target StoreStockton, CA

ShiseidoWindsor, NJ

Benefits: Issues:

Solar Roofs: Benefits & Issues

Economics not yet at “grid parity”

Underlying roof system must accommodate increased maintenance traffic

Underlying roof system must be designed to meet or exceed to expected solar system service life

Leak detection may be difficult Roof repair and maintenance

may be difficult if/when needed

Clean energy generated

Peak energy demands reduced

Roof Recycling: Reducing Landfill Waste

Cookson Elementary

SchoolTroy, Ohio

1

Windrow & Sweep

2

Cut & Stack

3

Chop

4

Grind Sieve & Package

5

Recycle

6

Benefits: Issues:

Roof Recycling: Benefits & Issues

Economics do not currently support

Only available in a regional pilot program for selected products

Logistics (removal, storage, transportation) are very difficult

Recyclers must have an assured supply before end markets can be fully developed

Currently limited to “down-cycling” in other products

Landfill waste reduced

Overall environmental impact reduced

Roofing materials will be thinner and lighter – all bringing new challenges for durability

Roofs will be installed with eventual removal in mind

Maintenance programs will become more sophisticated in order to extend service life

The primary concern of the building owner will continue to be durability

Commercial Roofing:Looking to the Future

dr. james l. hoff, dba introduction to low- slope roofing

Documents

roofing performance

low slope roofing slide

slope roofing systems

new roofing trends

commercial roofing industry

thermoplastic roofing

epdm thermoplastic roofing

costs of reroofing