How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What is the average life expectancy of an SPF roof?
Friday, June 22, 2018
You can expect an SPF (Spray Polyurethane Foam) to last 20 to 50 years, with an average of 30 years. The lifespan depends on two factors, and the first is the quality of the professional application. Polyurethane foam is created by mixing two chemicals under pressure at a spray nozzle head by trained applicator who applies the foam evenly over the roof surface. Problems with the chemical mix, temperature at application, or inadequate surface prep can reduce the lifespan.
But probably a more important factor is the protective coating applied over the foam, which is usually an elastomeric type. The coating protects the SPF from the sun’s UV rays and water intrusion. At about 20 years it begins to fail and, if the roof is not recoated, UV rays and water reach the foam and begin to deteriorate it. Recoating is necessary to extend the life of the roof.
If not recoated, small pits and pock marks form over the roof surface where the coating has worn down. Eventually, the pock marks open and form what looks like a mini-volcano, as water intrusion accelerates the process. You can see all the steps of the deterioration process going from left to right in the photo at the top of this page, and here’s a close-up below.
Once the roof gets to this point, re-coating is not possible and it must be torn off and replaced. Refreshing the elastomeric surface at 10 to 15 year intervals extends the life of the roof and 50 years, or possibly more, is reasonable with careful maintenance.
Here’s a bar graph that compares SPF life expectancy to other types of roof coverings.
Go to our blog post What is the average lifespan of the parts of a house? for rating of other house components. To understand the basis, potential use, and limitations of lifespan ratings, see our blog post ”How accurate are the average life expectancy ratings of home components? Are they actually useful?”
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To learn more about roofs and attics, see these other blog posts:
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