Spray Polyurethane Foam Roofing Systems
Spray polyurethane foam is often used for commercial roofing (and some flat-roofed residential roofing) because of its energy performance and durability. SPF roofing systems have been around for a long time, but because of a recent focus on energy-efficient building and an increase in code requirements, it is leading the pack in sustainable roofing system options. Unlike some traditional roofing systems, once installed it requires very low maintenance, and its thermal properties stand the test of time.
SPF roofing systems are ideal for most climates and commercial projects, including those that must endure severe temperatures or high wind. SPF roofing provides additional insulation to a roof, is lightweight, can be used to create appropriate slope to drainage, and is ideal for situations where the roof deck is an unusual configuration, since spray foam can easily fill and seal an irregular space as it cures.
SPF roofing systems have good adhesion to a variety of substrates, including metal, wood, concrete, asphalt shingles, clay tile, and built-up roofing (BUR).
Oak Ridge National Laboratories describes sustainable roofing systems as “roofing systems that have a long life, low maintenance, save energy, add durability to buildings, control moisture in buildings, and contribute very little to the waste stream.”
Installing and Maintaining SPF Roofing
Spray foam’s versatility lends itself well to roofing because it can be installed at various thicknesses to provide slope and meet thermal resistance requirements. Depending on the exact formulation and how it’s installed, high R-values are possible (6-7 per inch or greater), although it’s important to note that R-value is only one measure of a material’s energy efficiency.
In roofing systems, closed-cell spray foam is always used because it is rigid and water resistant. Mixed at the work site and applied to a substrate with a specialized spray gun, spray foam chemically bonds to the substrate to create firm adherence. Spray foam bonds well to many substrates including metal, concrete, wood, and BUR (built up roofing).
The Spray Foam Polyurethane Alliance (SPFA) published a Guideline for Roof Assembly Evaluation for Spray Polyurethane Foam (SPF) Roof Systems to help owners, architects, designers, and consultants in evaluating existing roofing systems to determine suitable re-roofing options using SPF.
The spray foam is then typically covered with a protective surface material—usually acrylic, silicone, or polyurethane—that provides extra weatherproofing and protects the spray foam from UV exposure. The coating also increases the spray foam’s fire resistance and can improve the roof’s aesthetic where this is an issue.
Once cured, spray foam roofing is an impenetrable, water resistant monolithic surface. Because of the lack of seams, SPF roofing systems eliminate one of the major causes of roof leakage.
Types of coatings used on SPF-based roof systems include:
Aromatic Polyurethane Elastomer
Aliphatic Polyurethane Elastomer
Modified Polyurethane Elastomer
Mineral particles, gravel, and/or sand may be added to a coating for increased surface durability.
Increased Demand for “Cool Roofing”
Again, this is an instance of changing energy codes driving building innovation. Cool roofing “strongly reflects sunlight and cools itself by efficiently emitting radiation to its surroundings” and is the fast-growing sector of US roofing. Growth is driven by the combined influences of energy costs and availability, material costs, building envelope performance requirements, legislative mandates/incentives, and advancements in roofing material technologies.
The U.S. Department of Energy (DOE) has mandated cool roofing for all of its buildings and facilities. The US Army plans to use cool roofs on all its facilities moving forward—up to 950 million square feet worldwide.
Originally cool roofing for SPF roofing systems meant applying a white coating, however new generation coatings can be almost any color.
According to the Cool Roof Rating Council, “Although white materials tend to be very good solar reflectors, colored roofing materials can also be made to reflect more sunlight. More than half of the sunlight reaching the earth is invisible to the human eye, and this invisible sunlight heats the roof. A colored surface that reflects much of the invisible sunlight is a called a cool dark color, or cool color. A cool dark color reflects more sunlight than a similar- looking conventional dark color, but less than a light-colored surface. For example, a conventional dark colored surface might reflect 20% of incoming sunlight, a cool dark colored surface, 40%; and a light-colored surface, 80%.
Graphic from the Cool Roof Rating Council website: coolroofs.org
Heat Island Effect
According to the EPA, “The term ‘heat island’ describes built up areas that are hotter than nearby rural areas. The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C). Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.
“On a sunny summer day, a typical roof surface can reach temperatures that are nearly 100°F above the ambient temperature. A cool roof, by contrast, stays at or near the ambient temperature due to the characteristics of its outer layer. There are many benefits to keeping a roof’s surface cooler, including air-conditioning energy and demand savings, monetary savings, increased human comfort both indoors and outdoors, and other positive impacts on urban environmental quality.
“In low-rise buildings, a typical application will achieve air-conditioning energy savings of approximately 10% to 20%. The energy savings achieved through cool roofing translate into monetary gains for building and facility owners, as well as help reduce emissions of atmospheric pollutants and greenhouse gases.”
How does cool roofing help?
Unlike conventional roofs, cool roofs stay at or near ambient temperatures even on the hottest summer day. Cool roofing is defined by the radiative properties known as solar reflectance and thermal emittance. A cool roof has a higher solar reflectance and higher thermal emittance than a non-cool roof. All surfaces absorb some solar energy as heat.
High solar reflectance and high thermal emittance of a cool roof combine to keep the roof surface much cooler than a traditional roof, with peak temperature reductions of 30°F–60°F. Achieving this type of drop in roof surface temperature will reduce the overall heat gain through the roof and reduce a building’s annual cooling needs.
Selecting an SPF Roofer
As with any spray foam insulation project, it’s important to select a manufacturer and an installer that are professional and carry excellent credentials. Applying spray foam is a very technical operation, and aside from the manufacturer and formulation, various factors come into play:
The environmental conditions at installation: SPF roofing should not be installed at too-low temperatures (the manufacturer will provide exact specs for each formulation) or when humidify is within 5 degrees of dew point. It should also not be applied during conditions such as ice or frost, or when there is excessive visible dampness on the roof area to be covered.
Overspray: Applicators should have a plan in place to make sure that adjacent surfaces do not accidentally get permanently covered with spray foam.
Fumes: A plan should also be in place to protect applicators and residents from fumes while the spray foam is curing.
Fortunately, as spray foam roofing becomes more and more popular, there is a wider selection of applicators and products available nationwide.
SprayFoamSuccess.com and the Spray Polyurethane Foam Alliance are great resources for finding SPF roofing system manufacturers, products, and installers.
The Lifespan of Spray Foam Roofing
An SPF roofing system is typically incredibly durable and rarely needs to be repaired or replaced. If a severe weather event occurs, it’s a good idea to inspect the roof and seal any small cracks or punctures with an elastomeric sealant. The coating on SPF roofing systems is usually recoated every fifteen years or so.
“In 1996 and 2003, the National Roofing Foundation commissioned Dr. Rene Dupuis of Structural Research Inc. to conduct research on SPF roofing systems in six different climate zones in the United States. Based on surveys of over 300 SPF roofing systems, Dupuis concluded that SPF roofs have an effective service life of more than 30 years. The research also shows that the physical properties of the foam change very little with age.”
Specific Energy Efficient Qualities of Spray Foam Roofing
Spray foam roofing is increasingly being recognized as an energy-efficient, sustainable roofing material, primarily because it is applied above the roof deck in a system and has a high R-value. Spray foam roofing systems are also generally covered with a light-reflective coating to prevent ultraviolet-induced surface degradation.
SPF roofing is also considered a sustainable, engineered building product for the following reasons:
It’s durable and therefore eliminates roofing garbage as traditional roof materials need to be periodically replaced.
It does not contain ozone-depleting chemicals.
Because the components of spray foam roofing transport in small drums that are combined on-site and then expand to fill a much greater space, money is saved on transporting what would otherwise be large amounts of solid materials.
Spray foam roofing can be applied over compromised existing roofing systems—including concrete, clay tile, wood, and metal—without having to tear down and dispose of the original roofing, thereby saving those materials from a landfill.
“Oak Ridge National Laboratories reported, “The need for multiple roofs makes roofing one of the largest contributors of solid waste.” According to a 1999 survey by the National Roofing Contractors Association (NRCA), more than 68.5% of the $11.3-billion low-slope re-roofing market includes tear-off and replacement of the existing roof membrane.”
As the demand for cool roofing that reflects light, reduces radiant heat, and insulates buildings becomes imperative, and builders and building owners become more environmentally aware, SPF roofing is the most popular new roofing material.