Spray polyurethane foam roofing

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By Mason Knowles

PlantServices.com

Keywords: roofing

What is it? How does it work?

Spray polyurethane foam roofing systems have been in use since the mid 1960s and have demonstrated service life well beyond 20 years.

Spray polyurethane foam was first used commercially in the early to mid 1960s for cold storage and industrial insulation projects. Because the material is water resistant, some of the pioneer contractors experimented with applying the systems on roofs. The mid 1970s saw application and substrate preparation techniques that led to today's standards.  The foam roofing experienced growing pains in two ways during its early years of use. First, although the contractors developed a high skill level in spray foam insulation application, they did not necessarily have knowledge of or skills in roofing. Some of the early premature installation failures are attributable to incorrect roofing details and techniques. Secondly, many traditional roofing contractors entered the spray polyurethane foam roofing market in the early 1970s to take advantage of the energy saving characteristics of spray polyurethane foam. Some of these contractors had insufficient training and knowledge that led to premature failure of the roofing systems they applied.

Fortunately, there emerged during this period a core group of knowledgeable and responsible contractors whose work exhibited quality and professionalism. By 1986, this core group grew into an industry guided by a national trade organization, the Polyurethane Foam Contractors Division of the Society of The Plastics Industry, Inc., recently renamed the Spray Polyurethane Foam Division (SPFD).

The SPFD formed volunteer committees comprised of engineers, scientists, contractors, suppliers, equipment manufacturers, inspectors, and material manufacturers. These committees developed over 27 technical guidelines and documents, including industry guidelines on roofing, cold storage, perimeter wall insulation, tank and vessel insulation, elastomeric coatings, position papers on thermal barriers, blisters, moisture vapor transmission, and many others. 

The committees developed accreditation programs for applicators, contractors, suppliers, and inspectors. To date, over 1,700 individuals participated in the accreditation programs. 

What is spray polyurethane foam?

Spray polyurethane foam roofing systems consist of an application of specifically designed covered with an elastomeric coating or aggregate covering to protect the foam from ultraviolet rays. Specialized equipment mixes two liquid components at the spray gun that applies foam to a prepared substrate. The mixed liquid expands to 30 times its original volume, forming a rigid foam plastic within 3 to 10 seconds, while chemically bonding to the surface on which it is sprayed. Spraying the foam in 1/2 to 1-1/2 inch lifts to a desired thickness (1" minimum) fills in low areas, builds in slope, and provides insulation. 

Spray polyurethane foam has a closed cell structure and is water resistant. It must, however, be protected by elastomeric coatings or aggregate coverings to prevent UV-induced surface degradation. Such coverings can also be used for other purposes, including inhibiting moisture vapor transmission, enhancing the aesthetics of the system, increasing the impact and abrasion resistance of the system, achieving flammability, and code requirements.

How long does it last?

According to recent surveys, spray polyurethane foam roofing systems are highly sustainable. The oldest performing spray polyurethane foam roofs are over 30 years old.

Since the physical properties of foam changes little with age, how long the foam system lasts depends primarily on the original application and long term maintenance. Spray polyurethane foam roofs, like other roofing systems, should be inspected semiannually and after events that could cause missile damage. Small (less than 4" in diameter) dents, cracks, punctures from dropped tools, wind driven missiles can be repaired with an elastomeric caulking compatible with the foam system. Since foam adheres to itself, more extensive damage can be repaired by removing and reapplying more foam. Recoat spray polyurethane foam roofing systems covered by elastomeric coatings every 8 to 15 years, depending on a variety of factors including thickness of coating, environment, physical properties, weathering, and warranty requirements.

When is it used?

Spray polyurethane foam roofing systems have excellent adhesion to a variety of substrates including built up roofing, modified bitumen, concrete, wood, asphalt shingles, clay tile, and metal. Since they add little weight and can be applied in any thickness to add slope and fill in low areas, these roofing systems are often used as a recover roofing system over existing roof coverings.

Hail and wind driven missiles can damage the spray polyurethane foam roofing system. However, the damage does not cause leaks. Furthermore, the damage can be repaired months later without compromising the long term performance of the roofing system.

Spray polyurethane foam roofing systems also excel when the following conditions exist:

• Additional insulation is required.
• The roof substrate has numerous penetrations.
• The roof deck is an unusual shape or configuration.
• The roof is in an area where severe weather such as high winds and hail storms are likely to  occur.
• Lightweight materials are required.
• Slope must be added to provide positive drainage.

Limitations:

One of the advantages of spray polyurethane foam roofing systems can also be one of its limitations. A crew of 2 to 4 persons can install spray polyurethane foam roofing systems. However, the crew must have a high degree of technical knowledge and experience in foam application including substrate preparation, roofing principles, equipment maintenance, and application skill.