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Installation of Tuff-R sheet foam - in-cavity/out cavity?

Installation of Tuff-R sheet foam - in-cavity/out cavity?


Old 10-06-08, 02:02 PM
Thread Starter
Join Date: Sep 2007
Location: New York
Posts: 22
Installation of Tuff-R sheet foam - in-cavity/out cavity?

I am redoing the plaster walls in a room in my house in New York (I am also opening up the wall cavities to redo the electrical wiring). I don't expect to find any insulation in my 2x4 walls (house built in the 1920's). I was thinking about furring out the walls to a true 2 x 6", then cutting three layers of the 2" tuff-r to fit within the wall cavities (between the now-2x6 beams), but leaving a 1/2 gap on the edges of the sheet foam, then using spray foam to seal the gaps. Follow with 5/8 water reistant gypsum, then two layers of plaster.

The TUFF-R claims to have 12.2 R value for 2 inches. Will I get that x 3 if I put in three layers of Tuff-R? Or, since the 2x6's won't be insulated themselves, will they leak heat?

Or, does it make more sense to leave the 2x4s as is, put two layers of 2" tuff-r in the cavity, then follow with a 2" sheet on the exterior of the studs? I'm trying to avoid losing too much floor space due to bumping the walls out.

I'm pretty sure that this would be cheaper than sprayed in foam by a contractor.

Any advice would be appreciated.
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Old 10-08-08, 06:56 PM
Join Date: Mar 2008
Posts: 9
I like plan B - leave the 2x4 studs alone, pack cavities, with rigid insulation, foam edges for complete seal, add layer of rigid to outside of house.

Some tricks will be needed to get the water plane right with existing openings (windows, doors) when you extend it 2".
I commented on a similar project in http://forum.doityourself.com/showthread.php?t=339797

I guess you have true, old-school, 2x4's not 1.75x3.5"

BTW, I'm doing a similar plan to this.

I'm curious if anyone has used products from insulationdepot.com which sells salvaged rigid insulation panels. This maybe a source for this project.

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