Today, we solved a tough flat-roof problem by hiring a foam contractor to spray polyurethane over an existing ‘flat’ gravel-and-tar lay-up roof.
The original tar and gravel is over 4″ thick straw matting. We’d made a number of cuts into the perimeter of this old roof…. exposing the straw. How the heck to close this up, and be assured of a strong watertight seal? This roof gets snowed on big time…
The foam guy solved all issues. All we had to do was set some new perimeter boards: 2x10s nailed alongside (and outside) the original cant strips. This gave us a deep bathtub that the foam guy sloped to a new, foamed-in, roof drain. Spraying from above, not below. Sweet. We’ll cap the 2x10s with metal later, once the final UV resistant layer is sprayed on – tomorrow.
A couple inches of this stuff dries in a matter of minutes. Five minutes and you can walk on it. It adheres to all surfaces, and supports itself on vertical surfaces. Foam guys says 2″ will support a man’s weight over a void. Also claims R7 per inch.
Something new for me – thought I’d share.
Replies
This the type of application where foam really proves itself. All the alternatives may be more expensive and take a lot more time.
I wouldn't count on 2" supporting you over a void though. Most people in the insulation field would say that the cured r value owuld be a little less than 7; more likely; morelikely 6 per inch.
Some poly foam is R7.2 or thereabouts, but for waterproof roofing a greater density is required, if it is going to last. more like R4 or 5.
you only think you have solved the problem. I have NEVER known of one of these that lasts the projected lifespan, and when it dos leak, it hides the source and makes it harder to diagnose and repair. When it finally does get replaced, there is a ton of rot repair to accompany it. I suppose that ten or fifteen percent of them do OK. Good Luck with yours.
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been thinking more about this - your foam guy - was he advertising as a roofer, or what is his background?
Reason I am suspicious is the reported density/R-value. I am picturing a guy who normally does insulation instead of roofs and gets the idea to push his product for roofing also since some urethenes are used and formulated for roofs.
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Taunton University of Knowledge FHB Campus at Breaktime.
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I hate to rain to your parade but I wouldn't take a foam roof for free. I've worked on dozens of them over the years and have never seen one that didn't leak after just a few years. You can never find the leak since by the time it drips through the foam is like big sponge full of water. Just got done trying to repair leaks on a commercial building with foam roofs 6 years old. The owner is finally giving up on repairs and having all the foam removed and conventional roofing installed.