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Web Exclusive: Sustainability of Spray Polyurethane Foam Roofing Systems
by Mason Knowles
January 3, 2006
Spray polyurethane
foam roofing can last 30
roofing systems for over 30 years. What they may not have known then is the high years or more with
proper maintenance,
degree of sustainable or green characteristics that these building materials exhibit. saving you money over
your building’s lifespan.
Building owners wanting to save energy have used spray polyurethane foam (SPF)
A sustainable roof must provide high performance, low maintenance and be easily
restored to initial performance levels. SPF meets each of these criteria. It forms a seamless blanket of
protection against the elements, has a long life, provides substantial energy savings, adds durability to
buildings and controls moisture in them, and resists wind uplift and impact damage. SPF is also a renewable
system that can be repaired easily and recoated indefinitely. It can be applied over existing roof coverings,
eliminating tear-off construction debris and disposal in landfills.
Long-Term Performance
Surveys conducted by Dr. Dean Kashiwagi of the Del E. Web School of Construction at Arizona State
University and Dr. Rene Dupuis of the National Roofing Foundation revealed that SPF shows little sign of
deterioration even after 30 years.
Dr. Kashiwagi is the pioneer of the “Performance Based Procurement System” for buying best performing
services/facility systems. Between 1983 and 1996, he surveyed the performance of more than 1600 SPF
roofing systems, the oldest of which were more than 26 years old. Of the roofs surveyed, 97.6% did not leak
and 93% had less than 1% deterioration— pretty good statistics considering 55% of those roofs were never
maintained.
In the most comprehensive roof survey ever performed by the National Roofing Foundation, Dr. Dupuis
evaluated 160 SPF roofing systems in California, Texas, Wisconsin, Illinois, New Jersey, and New York. In
presenting his findings, Dr. Dupuis concluded that SPF roofing systems appear to have a very high degree of
sustainability with an indefinite life expectancy when properly maintained with periodic recoating. Both
Kashiwagi and Dupuis also noted the physical properties of SPF did not diminish over time, and more than
70% of the roofs were applied over existing roofing systems.
Energy savings
Many large companies and institutions have documented energy savings from SPF
roofing systems. After studying more than 8 million ft2 of roofing, Texas A&M
concluded the energy savings paid for the cost of SPF retrofits within 3 to 4 years.
How do SPF roofs deliver such dramatic results? Black-surfaced roofs have
measured peak temperatures up to 190 °F on a 90 °F day. If the interior
A roof that utilizes spray
polyurethane foam
roofing material has
exceptional wind uplift
resistance and can
protect the building from
extreme heat and cold.
temperature is maintained at 78 °F, the resulting temperature difference is 112 °F.
Fasteners alone can reduce the effective insulation value between 1.5–31.5%,
depending on the number and type. On a hot summer day, typical dark-colored
membranes absorb radiant heat. The roof’s surface temperature rises. Thermal
bridges, such as fasteners and gaps in insulation boards, transport heat into the
building.
Spray polyurethane foam can help to keep energy costs low because it:

is applied above the roof deck;

reduces or eliminates thermal bridging;

has a very high aged R-value; and

is typically coated with light-colored, reflective coatings.
Durability
Oak Ridge National Laboratories (ORNL) reports: “The principal causes of
premature roof failure are moisture intrusion and lack of wind resistance. Moisture
in roofing systems leads to dripping, accelerated failure of the insulation and
membrane, structure deterioration, depreciation of assets, and poor thermal
performance. Similarly, the loss of a roof during a major windstorm not only causes
SPF is a very good
impact-absorbing
material. Hail and winddriven missiles rarely
cause leaks and damage
can typically be repaired
at a later date without
compromising long-term
performance.
structural damage, but also exposes building contents to the elements. The
insurance industry identifies roofing as the primary contributor to disaster-related
insured losses.”
SPF roofing limits moisture intrusion because of its 90% closed-cell properties.
Damage to the system typically does not cause leaks into the building, and
moisture intrusion is isolated to areas of damaged foam cells. As reported by Dr.
Dupuis: “One unique aspect of SPF roofs... is they are not in immediate danger of
leaking, providing the penetration does not extend all the way through the foam.”
SPF 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 (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
(BUR) and metal increased the wind uplift resistance of those roof coverings. FM’s testing showed similar
results for concrete, metal, and wood.
According to Dupuis and other industry experts, SPF is a very good impact-absorbing material. Hail and winddriven missiles rarely cause leaks and damage can typically be repaired at a later date without compromising
long-term performance. One of the most famous examples is the New Orleans Superdome. A severe hailstorm
damaged areas of the SPF roof in 1978, and the city debated for the next 10 years on how best to execute
repairs. Finally, in 1992, the roof was repaired and re-coated. Despite such a long time before repairs were
finally carried out, the roof never leaked from the hail damage.
Environmental Considerations
Environmental responsibility is an important consideration for sustainable roofing. The construction industry is
one of the biggest contributors to solid waste, and ORNL reports the need for multiple roofs makes roofing
one of the largest contributors of solid waste. According to the National Roofing Contactors Association 1999
survey, more than 68.5% of the $11.3-billion, low-slope re-roofing market includes the tear-off and
replacement of existing roof membranes.
SPF roofing systems are often used as a re-cover for existing roofs without tear-off, which greatly reduces the
amount of construction debris sent to landfill. A typical 10,000-ft2 SPF roofing project produces less than 0.5
yd3 of scrap and from 1 pt to 3 gal of waste solvent. Compare this to the typical 10,000-ft2 re-roofing
project, which produces more than 10 yd3 of construction debris from tear-off and application waste.
Mason Knowles
mason_knowles@plastics.org
About the Author: Mason Knowles is the executive director of the Spray Polyurethane Foam Alliance (SPFA) of
the American Plastics Council (APC).