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owners have used spray polyurethane foam (SPF) as a roofing,
insulation, and sealing product for many years.
Recent research and performance studies on SPF applications demonstrate many sustainable characteristics of the material. This
article is divided into two sections. The first section addresses SPF roofing and presents investigative research by René Dupuis
and Dean Kashiwagi, Spray Polyurethane Foam Alliance (SPFA) sponsored projects at Factory Mutual and Underwriters Labor-
atory, cool roof research by Lawrence Berkeley Labs, and articles written by roofing experts such as Thomas Smith and Patrick
Downey. Energy studies are courtesy of Texas A&M University.
second section addresses SPF applications to the interior of a
building. The article includes research by Mark Bomberg,
W.C. Brown, Robert Alumbaugh, M.K. Kumaran, N.V. Schwartz, Anthony Woods, and others, in addition to SPFA sponsored pro-
jects with NAHB Research Center and Oak Ridge National Laboratories (ORNL) and field investigations by private companies.
1: Solar absorbtivity.
As shown on Chart 1, black-surfaced roofs have measured peak temperatures
up to 190°F on a 90°F day. If the interior temperatureis maintained at 78°F, the resultant
temperature difference is 112°F.
figures reported by Mike Watts in1996, fasteners alone can reduce the
effective insulation value between 1.5% to 31.5%,depending on the
number and type of fasteners.Detail 1 shows what happens to a typical
roof on a hotsummer day. Dark-color e dmembranes absorb radiant heat.
The roof’s surface temperature rises. Ther al bridges such as fasteners
and gaps in insulation boards transport the heat within the building.
How does SPF reduce energy costs.
Performance studies and research suggest that SPF roofing systems can last 30 years or more. Additionally,they require low maintenance, are resistant to leaks caused by hail and wind-driven debris, are resistant to high wind blow-off, can add structural strength, and minimize moisture damage within the building envelope.ORNL reported, “The principal causes of premature roof failure are moisture intrusion and lack of wind resistance. Moisture accu-mulation in roofing systems leads to dripping, accelerated failure of the insulation and membrane, roof structure deterioration, depreciation of assets, and poor thermal performance. [See Detail 3.]Similarly, the loss of a roof during a major windstorm not only
causes structural damage but also exposes the building contents to the elements. The insurance industry identifies roofing as the primary contributor to disaster-related insured losses."SPF roofing systems limit moisture intrusion because of their 90% closed cell properties. Damage to the system typically does not cause leaks into the building, and moisture intrusion is isolated to the areas of damaged foam cells (see Detail 4). As reported by Dr.Dupuis, “One unique aspect of SPF roofs...is that they are not in immediate danger of leaking, providing the penetration does not extend all the way through the foam."
roofing systems have exceptional wind uplift resistance. Field
observations of SPF performance during Hurricanes Allen, Hugo, and
Andrew led the industry to conduct laboratory testing of SPF systems at
Underwriters Laboratories and Factory Mutual. SPF’s wind uplift
resistance exceeded the capacity of UL’s testing equipment. UL also
observed that SPF roofs applied over BUR and metal increased the wind
uplift resistance of those roof coverings. Factory Mutual’s testing
showed similar results over concrete,metal, and wood.According to Dr.
Dupuis and other industry experts such as Thomas Smith and Richard
Fricklas, SPF is avery good impact absorbing material. Hail and
wind-driven missile damage rarely cause leaks in an SPF roof. The
damage typically can be repaired at a later date with-out compromising
the long-term performance of the SPF roofing system.One of the most
famous examples is the New Orleans Superdome. As evere hailstorm
damaged areas of the SPF roof in1978. For the next 10 years, the city
debated how best to repair the damaged roof. Finally, in 1992, the
roof was repaired and re-coated. However, prior to the repairs,
the roof never leaked from the hail damage. (Some leaks were
reported that were actually caused from bullets fired at the roof
during Mardi Gras.)
|SPF Reduces Construction Debris
ORNL also reported, “The need for multiple roofs makes roofing one of the largest contributors of solid waste."According to the National Roofing Contractors 1999 Survey, more than 68.5% of the11.3 billion dollar low slope re-roofing market includes tear-off and replacement of the existing roof membrane.SPF roofing systems have excellent adhesion to a variety of substrates, including BUR, modified bitumen, concrete, wood, asphalt shingles, clay tile, and metal. Since SPF adds little weight and can be applied in various thicknesses to add slope and fill in low areas, SPF roofing systems are often used as a recover system over existing roofs without tear-off. Therefore, the application of SPF roofing systems over existing roof coverings greatly reduces the amount of construction debris in our landfills
So to conclude this section, SPF roofing systems demonstrate significant sustainable characteristics. SPF roofing systems have along life, are renewable, save energy, add durability to buildings, control moisture in buildings, and contribute very little to the wastestream. SPF roofing systems greatly reduce tear-offs in many re-roofing projects, which also decreases the amount of materials entering the waste stream.
SECTION 2: INSULATION AND AIR BARRIER SYSTEMS
Chart2: SPFR value aging curve
|“The durability of a material in a
building envelope depends on the outdoor and indoor climate, type of
construction, and conditions of service. A small change in one of these
variables may result in material failure during the first year or a
flawless performance for forty years."The use of SPF systems can
significantly affect the durability and climate control of a building.
Three SPF systems are used within the building envelope: high density
(1-1/2 to 2lb/ft3), low density (less than 1/2 lb/ft3), and sealant
foams. High density SPF isused when strength, high moisture resistance,
and high insulating value are desired. Low density SPF is used when
insulation, air barrier, and sound control are desired. Sealant foams
are used to caulk around windows, doors, sill plates, and other
locations to seal against unwanted air infiltration.
Factors affecting the R-value include: thickness of application (the thicker the foam the better the aged R-value), and the substrate and covering systems used (the lower the perm rated covering and substrate, the higher the aged R-value).1 5 Low-density (1/2lb), open-celled SPF typically has a stable, aged R-value ranging from 3.4 to 3.6 per inch (Chart2). In 1997, ORNL performed whole and clear wall testing of SPF between metal stud walls. Three quarters of an inch of high density SPF was applied between studs and 1/2" over the metal studs. Results confirmed that the use of SPF greatly reduces the thermal bridging effect of the metal studs.By controlling moisture infiltration, SPF also provides greater durability to buildings. The number one cause of building deterioration is moisture within the building envelope. Building performance in hurricanes and other catastrophic events can be adversely affected by moisture damage.
SPF conforms to unusual substrate configurations.
Typical SPF roof.
|Ozone Depletion and Global Warming
There are still some groups that consider SPF harmful to the environment due to the blowing agents used in the higher density foams. The following information should dispel that concern. Before 1992, most high density SPF used CFC 11 as the main blowing agent. From 1992 to the present, HCFC 141b has been the main blowing agent used in SPF. HCFC 141b will be phased out in the next couple of years. The most likely blowing agent candidates are blends of HFC 245fa, Pentane, or water.“The HCFCs and HFCs are considered environmentally superior to CFCs because they are largely destroyed in the lowest region of the atmosphere. The HFCs do not contain chlorine and have no potential to deplete ozone. HCFCs, however, do contain chlorine, but only a small percentage of that chlorine can affect the ozone layer; this is because most of the HCFCs released at ground level are destroyed in the lower atmosphere before they reach the stratospheric ozone layer."The global warming potential of a material is calculated by its total environmental warming impact (TEWI). The TEWI of a material is the total effect of the combination of direct (chemical) emissions and indirect (energy-related) emissions on global warming. In the case of insulation systems, the direct effect equals the total greenhouse gases released into the atmosphere. The indirect effect is calculated by estimating the equivalent carbon dioxide emissions based on how long the system remains in place before replacement and the total amount of fuel consumed. Because of the world’s dependence on fossil fuels for primary energy needs and the pre-dominant contribution of carbon dioxide to future global warming, energy efficiency is crucial in minimizing contributions to these issues. From 1980 to 1990, carbon dioxide contributed 55% of green-house gases that affect future global warming. CFC blowing agents(which were used at that time in SPF insulation) contributed 17% of greenhouse gases during the same time period. Replacing CFC blowing agents in foam insulation with HCFCs reduced the global warming potential of SPF insulations by 92%. SPF’s exceptional quality
reduces the amount of energy required for heating and cooling, thereby significantly reducing the amount of carbon dioxide released into the atmosphere.
SPF helped to seal repairs made to this existing roof.
Roof mounted HVAC units should be
raised and curbed, but
The global warming potential of a
gas is calculated from its energy absorbing properties over a specified
length of time. The longer it takes for a gas to be purged from the
atmosphere, the worse its global warming potential. It takes more than
500 years for carbon dioxide emissions to be purged from the
atmosphere. Even after 500 years, 19% of carbon dioxide survives to
affect global warming. Most HCFC 141b and HFC 245fa blowing agents have
left the atmosphere within 10 years.While most roofs are replaced
within 15 years, the wall insulation systems typically remain in place
until the building is remodeled or demolished. The longer the
insulation system remains in place, the more reduction to global
warming. SPF roofing systems are not replaced as often, there by
increasing their effectiveness in reducing global warming. Utilized as
an insulation system, SPF’s ability to provide effective air barriers
and control moisture increases its effectiveness in reducing global
SPF and Energy Costs of Production
“Comparative Energy Evaluation of Plastic Products and Their Alternatives for
Mason Knowles is the
Executive Director of the Spray Polyurethane Foam Alliance (SPFA) of the American Plastics
Council (APC) and recently served as the Technical Director of the American Plastics Council
on building and construction issues. He is a member of ASTM and chairman of D O8.06 Sub-Committee on Spray Polyurethane Foam Roofing Systems and ASTM Task Group Chairman for the revision of ASTM C-1029, Standard Specification for Spray Applied Cellular Polyurethane Insulation. Knowles has been in the polyurethane foam industry 33 years and has an
extensive background in SPF roofing, cold storage, industrial, commercial, and residential insulation applications, and has written and/or co-authored dozens of technical papers and articles on plastics and SPF.