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Discussion Starter #1
Can someone help me understand the permanence of Pink foam.
Everywhere I look online everyone says 1" is about 1.1 perms.
However when I look at the c-200/Codeboard pdf technical sheet
on the Owen Corning website is states it is .90 perms. Another technical sheet I found says .85 Perms. Then there is C-150 and C-250 which do say 1.1 perms, but I can't find anyone who even sells that product. Is that an older version and all the newer stuff has lower permanence?
Then no where can I find what the perm rating is for 1.5". Since its not
linear I can only just guess.
What I really need to know is whether 1.5" C-200 with a posted perm of .90/inch will meet the vapor barrier code in Ontario, which I believe is .7 perms?
 

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I love it when codes get attached to a wild guess. 0.7 would be acceptable but 0.8 would not, ridiculous. Once you paint the drywall you can add that barrier rating to the foam.

But, from a math point of view I'm going to take a guess. The question is, if the perm rating is 0.9 per inch, what is the resulting perm value for 1.5" thickness. I searched and also didn't see it specified, but if we use 0.9 for the first inch and 1.8 for the second ½" layer we can combine those values using the standard formula, the reciprocal of the sum of the reciprocals, a tongue twister, or simply the product over their sum. Using either the result is a perm of 0.6. But I doubt my math will satisfy them so you need to ask.

Bud
 

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Discussion Starter #5
Thank you for your responses.
I did email Owens Corning, but they haven't responded.

Also I noticed Dow brand CM20 on sale this week so I was thinking
of getting that, but looking at their technical sheet the vapor permanence
is 1.5 perms compared to 0.9 perms for Foamular.

I always thought XPS was all the same Blue or Pink, but apparently
there are differences.
 

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I agree, I've seen the differences, but from my work both 1.5 and 0.9 are low permanence, in the field they would both allow some drying to the inside.

But, once codes hang their hat on a number you often have no choice but to comply.

I'm a numbers guy so here is an example. When I started we had an old rule for converting blower door air flow to natural leakage, divide by 20. But then someone decided that they needed to fine tune that number for different factors so the drew up a map with numbers ranging from 15 to 25 (guessing). Ok, so now we divide by this more accurate number. However, when reading an article from the guy that pushed this fine tuning he said, the resulting answer will be within -50% to +100% accurate. With a tolerance like that it qualified as a WAG (wild a$$ guess).

Pinning down what perm will work and what one will fail is just another WAG.

My calculation should be close, assuming a linear change. If the CM20 is 1.5 per inch and you use 1.5" then the result would be close to 1.

Bud
 

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Discussion Starter #7
Ok I did some more research and read though the Ontario Building code on vapour barriers.
It says where insulation is used as the vapour barrier the thickness must be great enough that the permanence is no greater than 60 ng/Pa.s.m.
That's about 1 perm... I'm good!
 
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