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Spray Polyurethane Foam Roof Offers Protection Against Hail, Other Storms

By Joe Stockdale 

The right fit for the climate is a key concern when choosing a roofing system, and spray polyurethane foam (SPF) makes it an attractive option for many parts of the United States. This is notably relevant across the Midwest and South, where frequent thunder and hail storms are the norm, and a durable roofing system is needed to help handle Mother Nature’s wind and icy fits. 

It is the versatility spray foam offers, both through its application and how it resists wind and impact, that makes it a top choice for a variety of climates, including regions with severe thunder storms and hail, explains Will Lorenz, vice president of sales for General Coatings Manufacturing Corp. 

“As spray foam provides insulation directly to the roof, it reduces heat energy flow into or out of the structure,” Lorenz says. “Temperature changes on conventional roofs allow the building to expand or contract more, so these thermal dynamic forces cause splits and cracks; SPF reduces this effect so the building maintains a more waterproof and durable roofing system.”

Preventing Storm Damage 

Following 2012’s Hurricane Sandy, the Federal Emergency Management Agency (FEMA) took a close look at how various roofing and insulation materials hold up during extreme weather events. They found that spray polyurethane foam insulation is especially durable, serving as a reliable high-wind performer and also being more tolerant of impact, such as from hail, than other systems

Lorenz explains that to help support an effective roofing system for high storm damage areas, spray polyurethane foam starts by reducing the opportunity for air and moisture gaps. This helps provide a sturdy system that is resistant to winds and protects the substrate from wind-driven missiles, like hail. 

In 2015, the United States recorded 5,411 major hail storms, with the greatest number of storms occurring in June (1,324 storms), April (1,193 storms), and May (881 storms). But regardless of the time of year or the location, as states from Mississippi to South Dakota frequently find themselves dealing with hail storms, building owners and facility managers want the peace of mind to know that their roof can withstand major storms. And when there is damage, they want a roof that doesn’t have to be fully replaced, helping decrease maintenance expense.

The National Roofing Foundation report on spray polyurethane foam roofing systems by Rene Dupuis confirmed that where SPF roofs had experienced hail damage it was localized to the upper surface of the foam and most roofs were repaired rather than replaced. With the continuing trend toward sustainable construction, it is in the best interest of the building owners to repair rather than replace whenever possible and practical.

Texas saw the greatest number of hail storms in 2015, followed by Kansas, Nebraska, Oklahoma and South Dakota, but they do happen in all regions of the country. 

Spray Foam as a Roofing System 

Spray polyurethane foam is installed using a chemical blowing agent, which retains thousands of polymer cells inside after the foam is formed, creating a rigid, dense foam. This rigidity provides an air barrier, limits moisture ingress, and can add structural integrity to a building’s exterior. 

The most common application of SPF in a roofing system, to minimize damage from hail and wind, is a layer of at least 1 and a half inches, though usually around 2 to 3 inches of high-density closed-cell spray polyurethane foam covered with a minimum of 25 to 30 mils of protective coating is installed. 

The strength of the foam acts like a shock absorber against the impact of hail. And even though the top foam may be crushed, the lower foam levels remain intact, continuing to act as a moisture barrier. A basic SPF roofing system can typically withstand the average size of hail, slightly smaller than a golf ball, with only a small depression left in the foam and no cracks in the coating.  

Repair Instead of Replace

Considering the exterior membrane on non-SPF roofing systems acts as the waterproof layer, leaks are more apt to appear immediately following damage. But, according to Lorenz, SPF roofing systems continue to provide water resistance even when the coating may be damaged.

“Spray polyurethane foam has a very low water absorption and water transmission, so it doesn’t readily become saturated,” Lorenz explains. “So if the roof coating is punctured and even dented or broken, if it’s on the surface quarter inch, it can be repaired and recoated. [If] the damage is greater on depth or more frequent in hails hits, we can scarify or grind off the top half inch to one inch and then apply new foam and coating without tearing off the whole roof.” But Lorenz notes this would only need to be done on severe hail impact with dense hits or if the roof is neglected after the hail damage and not repaired in a reasonable timeframe.

And as with any roofing system, with an SPF roof it is important to inspect for and evaluate any damage following a major storm, to promptly and correctly make any needed repairs. Knowing and making the correct repairs to a spray polyurethane roofing system can allow it to continue to perform for years.

Type of DamageSize & SeverityExtent per 100ft2Recommended Repair
Light 1/2" diameter or less, less than 1/8” deep Less than 10 cracks, cuts and/or dents Coat and/or caulk dents, cuts and cracks
Note: Re-coat should be considered based on remaining service life of coating
    More than 20 cracks, cuts or dents Re-coat as required to cuts or dents fill in cracks
Note: Some caulking may be required to seal deeper cracks
Moderate 1/2" – 3/4" diameter, less than 1/4" deep Less than 10 cracks/dents Coat/caulk cracks
    More than 20 cracks, cuts or dents Recoat as required to seal cracks Note: Some caulking may be required to seal deeper cracks
Heavy 3/4" to 1-1/2” diameter, 1/4” to 1/2" deep Less than 10 cracks/dents Remove damaged SPF: Caulk holes and recoat as required
    More than 20 cracks/dents Scarf 1/2" of roof surface: Refoam and coat
Severe 1-1/2” or larger diameter, 1/2" or deeper Less than 10 crack/dents Remove damaged SPF: Caulk holes: Recoat as required
    More than 20 cracks/dents Scarf 3/4" of roof surface: Refoam and coat

Source: SPFA – 139: Recommendations for Repair of SPF (Spray Polyurethane Foam) Roof Systems Due to Hail and Wind Driven Damage

This chart is not specific to any region or climate zone, and varying climates may require additional recommendations for repairs to ensure the SPF roof continues to perform for years to come. For example, in hot arid climates, cracks in the coating can allow UV degradation, which affects the adhesion of the coating to the foam. These areas should be re-caulked or re-foamed even with light damage. In cooler climates, the main concern with damage is moisture saturating the spray polyurethane foam where the dent occurs due to long periods where snow or may stay on the roof and cause ice damming.

Joe Stockdale is industry relations manager, Accella Polyurethane Systems, a division of Carlisle Construction Materials Corporation. 

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posted on 2/2/2018