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Disadvantages of SPF Roofing Application

On the surface it sounds great; a quickie roof and good R-value. Those are two of the selling points of spray polyurethane foam (SPF) roofing, but this type of roof isn’t a perfect fit for all, or even most, commercial buildings. Before investing in any roof system, it pays to examine your options and research the pros and cons.

The standard SPF roofing application consists of three components, the substrate (often your roof deck), the SPF layer and the top coat. While SPF isn’t exactly new to the low-slope roofing industry, many professional roofers choose not to install this product due to some lingering issues.

Limited Installation Window

Installation specs are stringent for SPF, which can only be sprayed during specific weather conditions. The manufacturer stipulates a narrow range of outdoor temperatures and humidity levels. Pushing the installation window on either of these factors can negatively impact the roof’s integrity, showing up as interlaminar blistering in the foam. Even trace amounts of surface moisture on the substrate can result in the foam’s failure to adhere correctly. The optimal climate for applying an SPF roof is warm and dry with no wind. If your region is frequently cool, humid or breezy, it could be months until the weather conditions are acceptable for installing an SPF roof.


Sufficient roof drainage is essential for the welfare of a low-slope roof, and this is one area where applying SPF becomes critical. The worker uses a two-hose setup that delivers a combination of chemicals during the spraying process. Any variation in the way the worker applies the spray will result in uneven areas on the roof’s surface, creating “birdpaths.” These shallow ponds can hold water, which in turn decreases the life of the roof’s top coat.

Surface Prep

SPF is billed as being suitable to install over existing roofs, but in order to adhere correctly all loose gravel, metal or bits of old roofing must be completely removed before spraying. Skimping on roof deck preparation can reduce SPF’s adherence factor and reduce the useful life of the roof.

Insulation Factor

While SPF offers decent R-value when precisely applied, its thermal resistance is only as good as the worker controlling the spray foam mix. If the chemical ratio is even slightly off, the density of the foam layer is affected. Because SPF is hand-applied, the roof’s ultimate R-value is determined by the thinnest spot in the foam layer. Because of this, SPF roofing can only offer a theoretical R-value. When it comes to choosing the best overall insulation product for your low-slope roof, it’s hard to beat a tried-and-true product like polyisocyanurate (ISO) panels for uniform density and reliable R-value.


Fumes emitted during the spraying process present a potential hazard to employees or customers in or around the building. Rooftop HVAC units must be covered and the entire HVAC system shut down during spraying. SPF’s key ingredient, isocyanate, is hazardous when inhaled or when it comes into contact with the skin. Strict compliance with manufacturer and OSHA safety regulations is required. Likewise, the spray is lightweight and prone to sticking to anything it makes contact with. Even a slight breeze can deliver overspray to nearby structures, where it is extremely difficult to remove.

Examining Your Options

At North American Roofing, your satisfaction is our top priority. We deliver more than just top-notch roofs, we build customer relationships based on trust. We didn’t get to be one of the top roofing companies in the nation by taking shortcuts. Call us today to at 800-551-5602 find out what your roofing options are.

Posted on by North American Roofing
Disadvantages of SPF Roofing Application

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