I am replacing a 25 year old roof system and removed 3 layers of 1″ Thermomax double foil faced foam board. This is a full log cabin w/ vaulted interior ceiling. Large log purlins support the interior paneling, then 3″ of foam, then the decking and shingles. Originally the foam was stacked w/o any air spaces or proper venting on the cold side. So there was condensation issues and rotting. The outer most layer of foam is very brittle, but the 2 layers below seem pretty good. Full 2’x8′ sheets, edges aren’t banged up. Doesn’t appear that the 2 bottom layers had much water damage. So here’s the question: Is any of this foam still potentially worth reusing? We definately have varying opinions on the job. One is that all foam after 25 years isn’t worth anything, to it’s at least good enough for a garage and possibly reusing it in the new system. Who’s got an opinion on this?
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Replies
Wonder why they use multiple layers of foil faced. I have a single thick not foil faced poly iso spaced from roof deck and it seems to be working fine. 4" is about R66. 1" is about R 8.3. Been there about the same length of time. If its a matter of whether it still works how about calling a manufacturer or rigging up your own test box of used board with a light bulb, a thermometer, and compare it to a box made of new board. Tyr
I'll try call the manufacturer today. I thought about setting up a test like you described. In terms of why the stacking of it originally, I think that was a mistake. To get the best r-value I believe the foil faced should have an air space at least on the exterior side of it and probably between each sheet too. My understanding is that the foil acts as a reflector of radiant heat with the air space, but w/o an air space it actually conducts heat better thereby reducing its r-value. I'm of the camp that this foam does has some value left and considering the overall budget, it could be reused to increase the r-value of the entire system. We are only getting the new system to r-30 w/ a combination of new XPS and fiberglass batts. I would like to get it to as close to r-45 as possible.
Tyr, you wrote:
4" is about R66. 1" is about R 8.3. Explain the math on that.
Public school system.
Joe H
Don't know any math. I just read it off a scrap of poly iso that I had laying around. You got me! Tyr
Lot of products make outrageous claims, just like politicians.R8.3 original probably fades to R8 lifetime, so you have R-32 is all.But working with math, R-8.3 four inches twice gives 66.4, so maybe it was intended to be installed two-ply to provide that R-66
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They've been using Foam as an insulation material since about WW2
There are plenty of freezer panels out there much older than that and still in perfect condition..
UV exposure is what destroyes Foam, not age..
That's a good point. The water damage from condensation didn't help, but UV is the main degrader of foam.
They probably used layers because that was all that was available locally to them when that was built.. I prefer EPS foam for roof panels. It is not as high an R-value, but it does not gather water either. The Thermax can soak and retain water.
test it for moisture. If dry, it is fine to use except for the nail/screw holes in it that would allow some infiltration. I would be installing it with spray foam guns to seal joints.
Heat and UV are the things that do it in - probably why the top layer was weaker. It may have been exposed longer while under construction originally, and it got a lot of solar heat gain.
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