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Roof Insulation on Remodel

FloatingAdrift's picture

I am renovating a home we bought recently which has a cathedral ceiling.  The roof structure is comp. shingles over 1.5" rigid insulation over 1.5" T&G.  This assembly sits on the 4x10 rafters with the T&G exposed to the interior.   

We want to raise the R Value to 38 as economically as possible.  

My question is how to build a working insulation system over the existing rigid insulation to reach that R38? It looks like it's RMax which should be 9.6 R Value.  What would be the least expensive options for either a vented or non-vented assembly to get that to R38?

 

Cheep in the long run is often costly up front. (post #214523, reply #1 of 1)

I was shocked at the very low price quotes I got for closed cell spray foam last summer so I had three attics done that way. Apparently the price has really come down a lot or else contractors are hungry in Chicago. 

Insulation is more than just R value, this stuf is a total air seal too. The results are very impressive. 

In my humble DIY opinion, this is a no brainer choice. Just don't get seduced by the cheaper open cell foam, which could yield roof rot issues in this application.

 

Good luck.