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captoverus 11-29-2012 01:50 PM

Insulation on exterior wall
I have one poorly insulated exterior wall. Many years ago the former owners had cellulose insulation blown in to it. Rather than tearing it open and reinsulating it I was thinking I would use rigid foam board attached to the inside of the wall by adhesive with sheet rock over the foam board again attached with adhesive. Is this a good idea. Thanks for your input. Capt Overus

jklingel 11-30-2012 12:26 AM

why are you thinking of taking out the old cellulose? if it is not wet from a leak or whatever, i'd sure leave it alone. you can glue the foam to the present wall if you want, but i'd never glue sheet rock to foam and not screw it as well. do you have a vapor barrier in the wall (poly, visqueen....)? If so, it must be within the first 1/3 or the wall's total R value. Are you going to re-wire and hangs elect boxes on.... ??? You may have to install a new inner 2x4 wall. At least think that over; no idea what all your details are.

Gary in WA 12-01-2012 04:52 PM

Both the foamboard and drywall require positive fastening to the stud framing. Interior f.b. will cause the sheathing to remain cooler (dangerous if wet) and limit the walls drying to the inside ability. Hard to establish without knowing the wall material make-up... or house location for the sheathing dew point.


captoverus 12-03-2012 04:40 PM

Thanks for your replies. I live in suburban Philadelphia. The exterior wall is brick. The construction is pretty bad. Only about 2 inches inside between sheathing and interior wall. I was looking for the easiest solution. Mike

PS i don't get any email notification of replies. don't know if that is the way it is supposed to be.

Windows on Wash 12-03-2012 06:02 PM

Do you know what the outside, structural wall is constructed like?

As GBR mentioned, putting foam to the inside could make a previously dry wall become wet.

captoverus 12-04-2012 01:41 PM

question on insulation
the sheathing on the outside is black. Short of like a thick tar paper. And of course the brick is the outermost layer. I think the studs are 2 x 3

Windows on Wash 12-04-2012 03:42 PM

While the 2x3 aspect is a benefit to some extent, I would be very cautious about putting foam to an interior wall.

Its a recipe for disaster in many cases.

captoverus 12-05-2012 09:14 AM

OK. I guess I'll have to do it right. Thanks for taking the time to help me. Mike

Gary in WA 12-05-2012 08:43 PM

You are in Zone 4:

R-13 cavity insulation in the wood frame wall unless f.b. on exterior:

Notice where the foamboard is located and climates given:

IF the frame wall was gaped from the brick and you were able to wrap studs with fanfold for a thermal break (impossible because of the brick ties) then add cavity XPS, then drywall. F.b. on the inside would limit drying due to solar gain after a rain, unless ventilated, fig.1;


captoverus 12-05-2012 08:53 PM

Thank you for your time and advice. Mike

Gary in WA 12-05-2012 08:58 PM

You're welcome, we aim to serve DIY'ers!


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