What is polyurethane spray foam?

Last Updated on: 25th June 2023, 06:14 am

Polyurethane spray foam has been used as a roofing material for nearly five decades. Extensive testing through independent studies has shown that foam roofs are long-lasting, affordable, and excellent for waterproofing and insulation.

Sprayed polyurethane foam is based on two components: isocyanate and polyol, which must be fed through a heated and pressurized hose and applied to a roof surface with a spray gun. The components combine as they reach the roof surface, rising for about three seconds and curing in about 1 minute. 

As the liquid rises, a seamless, smooth, and stable layer is formed. The surface must be adequately prepared and clean (no oil or dirt should be on the roof surface) and outdoor conditions must not be at high humidity levels for the foam to self adhere effectively. No loose aggregate (gravel) should be on the surface, and the substrate should be securely attached to the roof surface. 

After the foam is applied, 1-2 layers of elastomeric cool roof coating (about 30mil) are used to protect the roof from ultraviolet rays and keep the roof surface temperature low, enhancing the efficiency of the foam underlying insulation.

Foam Roofing Advantages

Sprayed polyurethane foam (SPF) roofing has many advantages over traditional roofing materials such as BUR (built-up roof), PVC (polyvinyl chloride-based highly flexible plastic membranes), TPO (thermoplastic polyolefin), and EPDM (rubber roofing). The homeowners can extend the life of a foam roof to the life of the building by adding a layer of cool roof coatings to the foam roof every 5 to 15 years (depending on wear, location, and initial thickness). Foam roofs can last 20 or more years with virtually no maintenance, and extending roof life to 40 years or more requires very little.

The cost of installing a foam roof is about the same as installing a traditional roofing system and a similar level of insulation. Some benefits of foam roofing include:

PUR foam is the best insulator

Sprayed polyurethane foam consists of about 1 million cells per square inch, giving it R-values of 6 to 8 (depending on the formulation), and foam is airtight as well. Both of these factors make it superior to any traditional insulation type, and just one inch of foam will significantly improve the performance of any underlying insulation (by reducing surface temperatures and blocking air movement).

Foam is a lightweight material

SPF roofing material is incredibly light at 50lbs per square, compared to 800lbs or 100lbs respectively for BUR (built-up roofs) and single-ply roofing. This also means you can install the foam on top of an underlying roof substrate, which diverts landfill waste and preserves the environment. And, due to the lightweight and seamless nature of sprayed foam, it can be used to safely build up low areas to correct both roof sagging and ponding.

SPF is flexible

SPF foam will conform to any surface it is sprayed on, making it ideal for roofs with large amounts of protrusions such as vents, pipes, chimneys, skylights, ac units, and other equipment.

It is seamless

Polyurethane closed-cell foam creates a single seamless and waterproof barrier. The lack of seams or joints prevents the roof from having the weaknesses of traditional roofs that eventually result in leaks.

Long life

The foam roof lasts the life of the building. This also prevents landfill waste and conserves resources.

Ease of Installation

Roofing professionals can safely install foam while occupants are inside without interrupting any currently running operations.

Energy Savings

SPF foam roofing can save as much as 25% to 40% on cooling and heating bills, effectively paying for itself in the long run (possibly in as little as five years, depending on energy cost savings).

SPF Foam is Inherently Waterproof

Since polyurethane foam is made of millions of tiny closed cells, it remains waterproof, even if the coating is cracked or penetrated. For example, the New Orleans Superdome had thousands of hairline cracks due to hailstorm damage, yet no leaks occurred, even though no repairs were made for a decade. Only complete penetration of the foam (a hole all the way through) will result in a leak, and roofing companies can repair this to full function with an elastomeric caulking material.

Cool Roof Coatings

Elastomeric coatings can extend the life of a foam roof indefinitely by preventing exposure to ultraviolet light. Generally, a light-colored and reflective (cool roof) coating should be used. This keeps the roof surface temperature within 10-25 degrees F of the ambient temperature of the surrounding area.


Sprayed Polyurethane Foam Roofing (SPF roofing) is the greenest (most environmentally friendly) and economical roof for your home. SPF roofs are seamless, lightweight, making them a monolithic barrier against the elements, improving the quality of life within the structure, cutting energy costs, and diverting landfill waste. 

Energy star-approved cool roof coatings further enhance the performance of SPF roofs, keeping the underlying building both cool in summer and warm in winter. Sprayed polyurethane foam truly is the superior flat roof solution.


1 thought on “What is polyurethane spray foam?”

  1. Thank you for explaining that the cost of installing a foam roof is just the same as installing a traditional roofing system and can last 20 or more years, even without maintenance. We are currently renovating our home, and my father wants to install a foam roofing system. Knowing its benefits now, I should tell father to go for it and make sure to hire a reliable contractor to do the foam roofing system installation.


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