Spray Polyurethane Foam?

Spray polyurethane foam is a plural-component material created by blending isocyanate (A) and polyol (B) with heat and pressure. Chemicals A and B are sprayed in liquid form and react on contact to form a solid, lightweight, and fully adhered roofing membrane.
While spray foam has been around for a long time, it’s still relatively unknown to most facility managers and property owners. SPF has been used in various industries and applications since the 1940s, but it wasn’t until the late 1970s that it started being used in the roofing and building construction industry for its superior insulative qualities.
Modern spray polyurethane foam roofing materials come in open-cell and closed-cell grades. Closed-cell foam is primarily used in commercial roofing applications, while open-cell foam is typically used for interior insulation and soundproofing.

The Basics of Spray Foam Roofing

In spray foam roofing, the A and B components of SPF are blended and applied directly onsite with a specialized spray foam rig. The two chemicals, which are housed in separate containers, are pumped through high-pressure hoses to a mixing gun at a temperature of 115-130°F. To ensure a successful application, the proper amount of heat and pressure is imperative during the installation process.
As the foam cures, it solidifies to form a durable, seamless, lightweight, and waterproof membrane. SPF provides the highest R-value (the measure of thermal resistance) of any commercial roofing material and is suitable for use in nearly every type of climate.
The video below shows installers applying spray foam to various types of commercial roofing substrates.

Foam Density

The B component is what determines the density of the foam. To be strong enough for use in a commercial roofing application, the foam must have a density of at least 2.5 psi (pounds per square inch). Generally, a density of 2.7–⁠3.0 lbs. is needed for the foam to be rigid enough to walk on. Anything lower than a density of 2.5 lbs. is too soft to walk on without damaging the foam.

UV Performance

While SPF is an outstanding waterproofer and insulator, it offers little to no protection against the sun’s UV rays. To combat this problem, the foam must be coated with an elastomeric roof coating (e.g., silicone, acrylic, urethane, butyl rubber) to achieve the necessary level of UV protection.
Based on SPFA guidelines, we recommend a minimum of 20 mils of silicone coating. In certain cases, as much as 40 mils may be required—depending on the chemistry used and warranty requirements. Visit www.sprayfoam.org for more information on the application of SPF and roof coatings.
Recommended Reading: Which Roof Coating Performs Best?

Finding the Right Contractor

The installation of an SPF roofing system requires a great deal of knowledge of SPF chemistry and the use of highly specialized application equipment. For some contractors, it can take months or even years to become a proficient SPF roofing system applicator.
For those considering an SPF roofing system, take the time to properly vet potential contractors. Request to see job references, industry certifications, product samples, case studies, etc. In some cases, a contractor may be able to arrange a roof walk on a project they recently installed.

SPF application


Elastomeric coating application

The Pros of Spray Foam Roofing

Thermal Resistance (R-Value)

Spray foam roofing insulation has the highest R-value of any conventional roofing material. R-value measures a material’s ability to resist the flow of heat. The higher the R-value, the better the insulator. The R-value of roofing-grade SPF is approximately 6.5 per inch. However, it is widely held that SPF provides far greater insulation qualities than its R-value suggests.

Strength & Durability

Spray foam systems provide commercial roofs with an incredibly strong, yet remarkably lightweight, protective membrane. In fact, SPF systems, applied at a thickness of 1 inch or greater, are proven to enhance a building’s structural integrity.

Longevity

A properly installed and maintained SPF roofing system can last 30 to 40 years, if not longer. SPF systems must be recoated every 10 to 15 years to ensure the long-term performance of the system by not allowing the sun’s UV radiation to degrade the foam layer.

Seamless & Self-Flashing

Unlike conventional roofing systems, spray foam roofs are completely seamless and self-flashing. SPF is specially designed to conform and adhere to irregular shapes and surfaces. These qualities virtually eliminate the ability for water to enter sensitive areas of the roof such as seams, fasteners, penetrations, and other flashing details.

Ease of Maintenance

SPF roofing systems are easy to maintain. Minor damage can usually be repaired with roofing-grade mastic or specialized roof sealant. If the damage is severe, however, extensive repairs are going to be required to ensure that the system remains watertight, and the foam membrane is not exposed.
In any case, we highly recommend consulting with an experienced spray foam roofing contractor to conduct regularly scheduled roof maintenance inspections.

Quickly Installed

Compared to most other conventional roofing materials, SPF systems can be installed more quickly and are far less disruptive to building occupants. That’s because spray foam systems are applied directly to roof substrates and don’t typically require the removal of any existing roofing material.

Renewable & Sustainable

Because SPF roofing systems can be recoated numerous times, they produce little to no waste over the course of their lifespan. This offsets the landfill waste concerns and high costs that normally accompany a roof tear-off and replacement.
The materials that comprise spray foam roofing systems are also environmentally friendly.

The Cons of Spray Foam Roofing

Application Equipment

The application equipment for SPF materials is very expensive. While most roof coating spray rigs cost a spray foam rig—which includes an air compressor, generator, and enclosed trailer—can cost upwards of Constant maintenance is also needed, and the parts can be difficult to access quickly when issues arise.
Note: Though we do not sell or maintain spray foam equipment, we do recommend Spray Works Equipment to contractors looking to offer spray foam solutions to their customers. Visit www.sprayworksequipment.com to learn more.

Up-Front Cost

Cost-wise, spray foam roofs are comparable to many other commercial roofing systems, however, they are significantly more expensive than standard roof coating systems. SPF systems can cost anywhere from to per square foot, or more, depending on the roof size and required application thickness of the SPF material. There are a variety of other factors to consider, as well.

Limited Application Window

SPF roofing systems must be installed when temperatures are above 50°F and when humidity levels are relatively low. Depending on the region and time of year, this can delay or even prevent the installation of spray foam roofing systems.
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