MM reviews the sustainability characteristics of SPF roofing and insulations systems
SPF In Roofing Systems
Between 1983 and 1996, Dean Kashiwagi surveyed the performance of more than 1,600 SPF roofing systems. In 1998, Rene Dupuis published his evaluation of more than 160 SPF roofing systems in six different climates of the United States. Both studies found SPF roofing systems to be highly sustainable. In Kashiwagi’s 1996 study, the oldest performing SPF roofs were more than 26 years old. Of the roofs he surveyed, 97.6 percent did not leak and 93 percent had less than 1-percent deterioration— pretty good statistics considering more than half of those roofs had never been maintained. Kashiwagi and Dupuis also noted that the physical properties of SPF did not diminish over time and that more than 70 percent of the roofs were applied over existing roofing systems.
Many leading companies and institutions have documented energy savings from the use of SPF roofing systems. A Texas A&M study calculated the energy consumption of their buildings before and after implementing such a system. After studying more than 743,224 m2 (8 million sf) of roofing, they concluded that the energy savings paid for the cost of SPF retrofits within three to four years.
How do SPF roofs deliver such dramatic results? Consider the performance of a typical roof on a hot summer day. Blacksurfaced roofs have measured peak temperatures up to 87.8 C on a 32-C day (190 F on a 90-F day). Thermal bridges, such as fasteners and gaps in insulation boards, transport heat into the building; fasteners alone can reduce the insulation’s effectiveness by 1.5–31.5 percent, depending on the number and type of fastner. By contrast, SPF roofing systems reduce these inefficiencies by:
- eliminating thermal bridging by providing a continuous layer of insulation over existing thermal bridges in the roof deck and/or assembly;
- providing a very high aged R-value of 6–7 (per inch); and
- typically including a light-colored, reflective coating.
Performance studies and research suggest SPF roofing systems can last 30 or more years. Additionally, they require little maintenance, resist leaks caused by hail and wind-driven debris, resist highwind blow-off, can add structural strength, and minimize moisture damage within the building envelope. SPF roofing limits moisture intrusion because of its 90-percent closed-cell properties. Damage to the SPF system typically does not cause leaks into the building, and moisture intrusion is isolated to the areas of damaged foam cells.
SPF roofing systems also 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 (UL) and FM Global. Imagine UL’s surprise when SPF’s wind uplift resistance actually exceeded the capacity of their equipment. UL also observed SPF roofs applied over a built-up roof and metal increased the wind uplift resistance of those roof coverings. FM’s testing showed similar results for concrete, metal, and wood roofs.
One of the most famous examples is the New Orleans Superdome. A severe hailstorm damaged areas of the SPF roof in 1978, and for the next 10 years the city debated the best method of repair. Finally, in 1992, the roof was repaired and recoated. Despite the long span of time before repairs were finally carried out, the roof never leaked from the hail damage.
According to the National Roofing Contractors Association’s 1999 survey, more than 68.5 percent of the $11.3-billion, lowslope reroofing market includes the removal and replacement of existing roof membranes.
Because SPF roofing systems display excellent adhesion to a variety of substrates, including built-up roofs, modified bitumen (mod-bit), concrete, wood, asphalt shingles, clay tile, and metal, they are often used to re-cover existing roofs without removing them. As such, SPF installed over existing roof coverings greatly reduces the amount of construction debris sent to landfill.
SPF In Insulation and Air Barrier Systems
Environmental control within a building envelope depends on regulating stable interaction between heat, air, and moisture. To control these factors, one must have continuous air barriers, rainscreens, weather barriers, and thermal insulation so gaps do not compromise the designed climate control. The durability of material in a building envelope is influenced by the outdoor and indoor climate, type of construction, and conditions of service. These variables will determine whether the material fails during the first year or demonstrates flawless performance for 40 years.
SPF systems can significantly affect the durability and climate control of a building. Three forms of SPF are typically employed within the building envelope: high-density (24 kg/m3 to 32 kg/m3 [1.5 pcf to 2pcf]) SPF is used when strength and high moisture resistance and insulating values are desired. Low-density (less than 8 kg/m3 [0.5 pcf]) SPF is called for when insulation, air barrier, and sound control are desired. (Editor’s Note: See “Learning the Difference between 1/2-lb and 2-lb SPF” for more about high- and lowdensity foam.) Sealant foams are used to caulk around windows, doors, sill plates, and other locations to seal against unwanted air infiltration and exfiltration.
Learning the Difference between 1/2-lb and 2-lb SPF
Half-pound SPF (also called low-density SPF ) refers to generic SPF weighing between 6.4 kg/m3 and 9.6 kg/m3 (0.4 pcf and 0.6 pcf) when fully cured. Spray-applied to a substrate, it expands approximately 150 times its original volume to form a semi-rigid, non-structural plastic. This SPF typically has an R-value of approximately 3.5 per 25.4 mm (1 in.) and typically uses water as the blowing agent.
Two-pound SPF (or high-density SPF ), on the other hand, weighs between 24 kg/m3 and 32 kg/m3 (1.5 pcf and 2 pcf) when fully cured. The material is used in interior applications, spray-applied to a substrate, before expanding approximately 35 to 50 times its original volume and forming a rigid plastic with a compressive strength between 103.4 kPa and 172.4 kPa (15 psi and 25 psi). This SPF has an aged R-value of approximately 6 per 25.4 mm (1 in.) and relies on hydrochlorofluorocarbons (HCFCs) or hydroflurocarbons (HCFs) as its blowing agent.
Spray foam similarities
Both 1/2 -lb and 2-lb SPFs are made from blended systems of polyol resins, catalysts, surfactants, fire retardants, and blowing agents on the B-side, with polymeric methylene diphesocyanate (MDI) on the A-side. The difference between SPF types is in how these materials are formulated—just as a baker makes dozens of different breads using water, yeast, and various flours, the SPF systems manufacturer creates several different SPFs from only a few ingredients.
All SPF plastic insulation is required by building codes to have a 15- minute thermal barrier covering the insulation on interior applications, unless the application is exempted in the code and approved by a building code official. Approval in this case would be based on full-scale fire tests specific to the particular situation. Spray foam, like most other organic materials, is combustible. It is formulated with flame retardants to decrease the flame spread as measured by ASTM International E 84, Test for Surface Burning Characteristics of Building Materials, and other tests. However, these flame-spread ratings are used solely to measure and describe properties of products in response to heat and flame under controlled laboratory conditions and do not necessarily reflect reactions to real-life fire conditions.
Generally accepted tests for thermal barriers and building assemblies include:
- ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials
Underwriters Laboratories Inc. 1715, Fire Test of Interior Finish Material
UL 1040, Insulated Wall Construction
FM Approval 4880, Class I Insulated Wall or Wall & Roof/Ceiling Panels; Plastic Interior Finish Materials; Plastic Exterior Building Panels; Wall/Ceiling Coating Systems; Interior or Exterior Finish Systems
National Fire Protection Association 286, Methods for Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth.
Safety and health issues
Care should be exercised during the handling, processing, and application of SPF—one must read the manufacturers’ and suppliers’ material safety data sheets, product labels, and installation instructions, as well as follow any local, state, or federal regulations and requirements.
Aerosols created during the spray foam application phase can be harmful to the applicator and those in the immediate vicinity. The installer should make appropriate use of personal protective equipment to help avoid breathing fumes and to keep liquid components away from the skin or eyes. The installer should also minimize exposure risk to building occupants during spray operations.
Cured SPF is relatively inert and has not been cited as a problem to allergy sufferers or to those with chemical sensitivities. Depending on the ventilation in place, odors and fumes can dissipate to nondetectable levels within minutes or hours of spraying.
Spray foam differences
Despite the qualities shared by 1/2 -lb and 2-lb SPF, the architect/engineer will select the proper material based on how each SPF type’s unique properties will address the site’s needs and priorities. Installation Half-pound SPF is normally spray-applied to the desired thickness with one pass, while 2-lb SPF is spray-applied at lifts from 12.7 mm to 38 mm (0.5 in. to 1.5 in.) until the desired total thickness is achieved. Excess foam can be trimmed easily with saws or knives, though most applications do not require full stud thickness (making trimming unnecessary in most cases). For example, SPF installed at 51-mm (2-in.) thickness between 2×4 studs requires a minimal cleaning on the stud face. However, SPF installed to full stud thickness requires additional trimming with a specially designed trimming tool. Sound absorption Both 1/2 -lb and 2-lb SPFs have air barrier qualities that can help reduce noise from outside the building envelope (e.g. airplanes and car traffic). The 2-lb foam’s density offers additional sound absorbing qualities. However, neither foam is exceptionally effective at reducing vibrational impact noises.
Moisture generally enters the building envelope in one of two ways— water vapor diffusion and air leakage. As mentioned previously, the excellent air barrier qualities of both 1/2 -lb and 2-lb SPF help reduce air leakage, but the foam types differ when it comes to vapor diffusion.
The higher a material’s permeance, the faster water vapor can pass through. Controlling water vapor within a building is important in preventing condensation, mold growth, and subsequent damage to building components. There are two basic types of moisture control within buildings:
- The ”flow-through design,“ which allows water vapor to pass through the building assembly’s components without condensing; The “vapor retarder design,” which limits the moisture entering the building assembly altogether.
A 1/2 -lb SPF ranges between 6 perms and 10 perms, with a 76-mm (3-in.) thickness of material. Its high permeability allows for the fairly rapid diffusion of water vapor, so the material often requires a vapor retarder element in the building assembly. In some cases, this could be part of the assembly, and requires no additional vapor retarder material. (When this is necessary, it is typically used on the insulation’s warm side.)
Two-pound SPF typically has a permeance of less than 1 perm at 76 mm (3 in.) and can be used in flow-through designs without a vapor retarder. Exceptions include situations where there is a constant vapor drive in one direction (e.g. natatoriums and cold storage facilities), or when there is a vapor retarding material on the assembly’s cool side.
Half-pound SPF has a high open-cell content (greater than 50 percent) and water can enter the foam. Conversely, 2-lb SPF has a high closedcell content (greater than 90 percent) and resists water absorption. In a building assembly, the latter SPF offers greater weather or rain barrier protection.
Until about 20 years ago, 2-lb SPF employed chlorofluorocarbons (CFCs) as its blowing agent, a compound that then became known for its significant upper-ozone-depleting characteristics. In the late 1980s, the industry moved away from CFCs and by 2005, spray foam providers had implemented non-ozone depleting agents such as HCFCs and HCFs. By contrast, 1/2 -lb SPF is formulated with water as a reactive blowing agent and does not contribute to atmospheric depletion.—M.K.
SPF’s aged R-value varies with the formulation, blowing agent used, and application. For SPF used in insulation and roofing applications with a density ranging from 24 kg/m3 to 48 kg/m3 (1.5 pcf to 3 pcf), aged R-values typically range between 5 and 7.5 per 25 mm (1 in.). R-value may be affected by application thickness (the thicker the foam, the better the aged R-value), substrate, and covering systems used (the lower the perm-rated covering and substrate, the higher the aged R-value). Low-density (8 kj/m3 [0.5 pcf]), open-celled SPF typically has a stable aged Rvalue ranging from 3.4 to 3.6 per 25 mm (1 in.).
In 1997, Oak Ridge National Laboratory (ORNL) performed whole- and clear-wall testing of SPF between metal stud walls. They applied high-density, 19-mm (0.75-in.) SPF between the studs, with an additional 13 mm (0.5 in.) applied on top. Results confirm that SPF greatly reduces the thermal bridging effect of metal studs.
SPF can add structural strength to buildings. Testing conducted by the National Association of Home Builders’ (NAHB’s) research center shows SPF insulation between wood- and steel-stud wall panels increases rack and shear by a factor of two or three when sprayed onto gypsum wallboard and vinyl siding, and increases racking strength by 50 percent when sprayed onto oriented strandboard (OSB). “During a design racking event, such as a hurricane,” concludes NAHB, “there would be less permanent deformation of wall elements and possibly less damage to a structure braced with SPF-filled walls.”
SPF provides better climate and moisture control by:
- providing a continuous air barrier;
- preventing moisture infiltration through air leakage;
- minimizing dew point problems and condensation;
- avoiding thermal bridging;
- resisting heat movement in all directions; and
- providing reliable performance under varying climatic conditions.
Better climate and moisture control saves energy, makes a building more comfortable, and reduces deterioration, thereby extending the life of a structure. SPF’s climate control ability reduces a building’s need for heating and cooling equipment, further lowering energy use and upfront costs. Side-by-side energy efficiency comparisons have shown up to 40-percent energy savings by using SPF over commonly specified insulation materials.
Furthermore, by controlling moisture infiltration, SPF increases a building’s durability. The number-one cause of building deterioration is moisture within the building envelope. Moisture damage can also worsen many buildings’ performance in hurricanes and other catastrophic events.
Ozone depletion and global warming
Some groups still consider SPF harmful to the environment because of the blowing agents used in the higher-density formulations.
Before 1992, most high-density SPF used CFC-11 (a chlorofluorocarbon) as the main blowing agent. From 1992 onward, however, HCFC-141b (a hydrochlorofluorocarbon) has been the blowing agent of choice. (HCFC-141b will be phased out in the next couple of years. The most likely replacement candidates include blends of HFC-245fa [a hydrofluorocarbon], pentane, or water.)
HCFCs and HFCs are considered environmentally superior to CFCs because they are essentially destroyed in the lowest region of the atmosphere. HFCs do not contain chlorine and have no ozone depletion potential. While HCFCs contain chlorine, only a small percentage can affect the ozone layer 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 (GWP) 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 total greenhouse gases released into the atmosphere. The “indirect effect” is calculated by estimating the equivalent carbon dioxide (CO2) emissions based on how long the insulation system remains in place before replacement, along with the total amount of fuel consumed.
Carbon dioxide contributed 55 percent of the greenhouse gases affecting global warming between 1980 and 1990. CFC blowing agents contributed 17 percent of greenhouse gases during the same period. Replacing CFC blowing agents in foam insulation with HCFCs reduced SPF’s GWP by 92 percent.
The GWP 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 GWP. It takes more than 500 years for CO2 emissions to be purged from the atmosphere. Even after 500 years, 19 percent of CO2 survives to propagate global warming. Most HCFC- 141b and HFC-245fa blowing agents leave the atmosphere within 10 years.
Energy costs of production
Franklin and Associates Ltd.’s study, Comparative Energy Evaluation of Plastic Products and Their Alternatives for the Building and Construction and Transportation Industries, compares the total energy requirements for the manufacture of plastic alternatives.
The unique feature of this type of analysis is its focus on all the major steps in the manufacture of a product—raw material extraction from the earth, fabrication, and even transport—rather than a single manufacturing step.
The study concludes that plastic products in the building and construction industry use less energy from all sources than other materials. According to the Franklin study, polyurethane foam insulation saved 3.6 trillion kJ (3.4 trillion Bru) in manufacturing energy over fiberglass insulation in 1990. To get an idea of how much energy this equals, consider 1.1 trillion kJ (1 trillion Bru) is equivalent to almost 170,000 barrels of oil, and 28.3 million m3 (1 billion cf) of natural gas.
As mentioned earlier, SPF helps reduce tear-off debris in roofing applications. SPF’s on-site application process generates very little debris and waste. A typical 929-m2 (10,000-sf) roofing project produces less than 0.4 m3 (0.5 cy) of scrap SPF, tape, and plastic (used for masking), and from 1 pint to 3 gallons of waste solvent (depending on the type of protective covering used). Compare this to the typical 929-m2 reroofing project, which produces more than 7.6 m3 (10 cy) of construction debris from tear-off and application waste. At present, so little scrap SPF is produced that material recycling is practically impossible.
About the Author
Mason Knowles is the president of Mason Knowles Consulting, LLC (www.masonknowles.com), a consulting company specializing in providing technical information, education and training for the SPF industry. He is also the chairman of ASTM D08.06 Subcommittee for Spray Polyurethane Foam Roofing, chairman of the ASTM Task Group C 1029, Spray Polyurethane Foam Specification, former executive director of the Spray Polyurethane Foam Alliance, and former technical director for the American Plastics Council.
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