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:

• Why is my roof sheathing sagging between the trusses?

• Why is granule loss a problem for an asphalt shingle roof? 

• What are the mistakes to avoid when doing attic improvements?

• What causes roof shingles to curl up at corners?  

• What causes shingles to buckle along a line on the roof?

• What causes leaks at a fake roof dormer? 

• What causes a sagging roof ridge line?

• What causes bubble-like blisters in a built-up and gravel roof?  

• Why does it cost so much more to replace a steep roof than a low slope roof? 

• What is "ponding" on a flat roof?

• Is an attic required to have a light by the building code? 

• How can I inspect my roof for hurricane damage?

• Why is premature curl of roof shingles a problem?

• How can I tell if a roof has more than one layer of shingles? 

• What are the common problems with attic insulation? 

• What is the life expectancy of an asbestos cement shingle roof? 

• What's the average lifespan of a roof?

• Why is it a mistake to replace a roof and not replace its flashings? 

• Are roof trusses better than roof rafters (stick framing)? 

• Why is a popped nail in a shingle roof a problem? How do I fix it?

• What are the most common problems with wood roof trusses?

• Why do my dormer windows leak? 

• Do home inspectors go on the roof? Do they get in the attic?

• Should I put gutters on the house? 

• How much of a roof truss can I cut out to make a storage platform in the attic? 

• What's the difference between an "architectural" and a regular shingle roof? 

• What does a home inspector look for when examining a roof? 

• Do stains on the ceiling mean the roof is leaking?

• How can I tell if the house needs a new roof?  

• Why does my homeowner's insurance want a roof inspection?

• What are the hazards to avoid when going into an attic? 

    Visit our ROOF AND ATTIC and LIFE EXPECTANCY pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.