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-   -   I have a "Poor Man's Spray Foam" question (http://www.diychatroom.com/f103/i-have-poor-mans-spray-foam-question-114413/)

Skull Leader 08-17-2011 10:39 PM

I have a "Poor Man's Spray Foam" question
 
I'm looking to do the "Poor Man's Spray Foam" as seen in one of HomeInsulation's youtube videos.

My walls are only 2x4's. I live in one of the coldest places in the US. Last winter we were the coldest place in the US one day at -59. I'm going to be doing this to about 1/3 of my home's exterior walls while renovating a kitchen and living room.

The question I have is can I put both a 2" piece and a 1" piece of Tuff-R on top of each other for an R value of about 19.5? Or will this cause condensation problems or some other problems I'm not forseeing?

Thanks!

AGWhitehouse 08-18-2011 01:43 PM

This is a tough installation to complete effectively and you still have a 1/2" void that allow for convective air currents. You'll also have alot of waste with the custom cuts, which is very costly garbage.

Below is a comparison of two systems...Noting the different R-values, I think you'd be better off in installation time, $, and stress level to fill the bays with unfaced batts. and sheath the wall with 1/2" foil-faced polyiso before you sheetrock. The foil-face with taped seams and penetrations will give you the air and vapor barrier needed while greatly reducing the thermal bridging that the studs create.

A whole different approach is to sheath the exterior of your house with nail-base foam panels. This would require re-siding, so I'm not sure if this is even in your deck of cards.

OOPS...done quick and without great review, the titles of the charts are backwards. The cut foam scenario is on the right...


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