dr. james l. hoff, dba introduction to low- slope roofing
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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
Historical Background
1840s – 1970s: Built-Up Roofing
Historical Background
1840s – 1970s: Built-Up Roofing
• 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
Historical Background
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
Historical Background
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
Historical Background
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
Roofing System Overview
EPDM
+ Large panel sizes for fast coverage
+ Outstanding resistance to weathering
+ High elongation to accommodate building movement
Roofing System Overview
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
Roofing System Overview
EPDM: Ballasted System
Roofing System Overview
EPDM: Ballasted System
Roofing System Overview
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
Roofing System Overview
EPDM: Adhered System
Roofing System Overview
EPDM: Adhered System
Roofing System Overview
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
Roofing System Overview
EPDM: Mechanically Attached
Roofing System Overview
EPDM: Mechanically Attached
Roofing System Overview
Thermoplastic
+ Heat-reflective white surface
+ Fast, simple welded panel seams
+ Available in variety of colors
Roofing System Overview
Thermoplastic Installation
Roofing System Overview
Thermoplastic Installation
Roofing System Overview
Asphalt
• Built-Up Roofing•BUR
• Modified Bitumen•APP•SBS
Roofing System Overview
Built-Up Roofing (BUR)
Insulation
Cover Board
Ply Felts SetIn Asphalt
Gravel Surfacing
Roofing System Overview
Built-Up Roofing (BUR)
Roofing Felts in Hot Asphalt
Roofing System Overview
Built-Up Roofing (BUR)
Gravel-Surfaced BUR
Roofing System Overview
Modified Bitumen
Insulation
Cover Board
Base Sheet
Cap Sheet
Roofing System Overview
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
Roofing System Overview
Modified Bitumen
Hot Mopped
Cold Applied
Torch Applied
Roofing System Overview
Modified Bitumen
Roofing System Overview
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
Roofing System Overview
Performance Features
Roofing System Overview
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
Roofing System Overview
Drainage Issues
Slo
pe
Typical2-WayStructural Slope
Interior Drain (Typ.) Typical2-WayStructural Slope
Roofing System Overview
Drainage Issues
4-WaySlope usingTaperedInsulation
Roofing System Overview
Drainage Solution
Roofing System Overview
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
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