Disadvantages of SPF Roofing Application

Posted by Heather Johnson in Common Roof Problems

17 August, 2012


Disadvantages of SPF Roofing Application - North American Roofing

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.

7 thoughts on “Disadvantages of SPF Roofing Application

  1. I have a flat roof,1300 sf in central phx, slight repair along south downspouts showing water damage with paint on inside. Would like an estimate for repair and new roof.This friday,1/15, works for me. Please contact me…602 418-0396….Thanks & Happy New Year!

    • We have sent your request to our technical department and someone should be in touch with you soon.
      Thank you for your interest in North American Roofing.

  2. Major disadvantage of foam roof not listed here is that they are not designed for taking any kind of weight. So if you have a roof with HVAC equipment or an elevator control room in a penthouse and equipment needs to be serviced by walking across the roof, its going to trash the roof. Delamination results in blistering and distortion of the roof suface which leads to pooling water and poor drainage, among other issues.

  3. Will hail damage these types off roofs ? My mother in law just had hers recorded with the roll on stuff you buy at Home Depot..and we had a couple hail storms since then and we see new water spots in the house over that area..What should we do ?

    • Dave – While we do not do any residential, we can advise that it might be best to at least have someone inspect your roof. Many times it is better to get to the leak while it is small instead of waiting for it to get bigger. Thanks for your comment.

  4. I have a flat top foam roof and live in ABQ, NM. It’s 12 years old, has several blisters and was covered with rocks and never sealed. It’s leaking around the Air Conditioner because the company that installed it did not level it so it leaked on the back side causing the foam to rot with a leak to my ceiling. We are looking at a new roof, but don’t know ‘how’ we can tell if the rest of the foam roof is good enough to have anything put on top of it. It’s hard to tell by just looking, besides all the blisters, which my roofing company refused to repair stating they don’t ever cause problems. Is there a reasonable way to check to see if the foam on the rest of the roof is still good?

    Thank you,

Leave a Reply

Your email address will not be published. Required fields are marked *