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Insulation in 2x4 walls

Posted by Noctua (My Page) on
Tue, Aug 6, 13 at 19:45

Wondering if i can buffer the insulated interior walls by puting 2 inch xps on the exterior.

Currently i am down to the studs, 2x4 as mentioned, and was thinking sound proofing batts (higher r value) on the inside with the xps on the exterior. The sheathing is shiplap board.

I was concerened this would hold the mosture in.

Short of that i thought i could add 2 inch strips to the 2x4 to makeshift 2x6 but would not prefer it as the interior is small enough.

What the options are there for 2x4?

Follow-Up Postings:

RE: Insulation in 2x4 walls

If you are willing to take down sheetrock, I would look into just reinsulating with dense pack cellulose insulation. It has a much better sound dampening quality and then add quiet rock (special sheetrock) to the side you took down.

RE: Insulation in 2x4 walls

I believe the interior finish has been removed.

What is the climate? What will the new exterior cladding be? Would 1" XPS be enough?

RE: Insulation in 2x4 walls

OP is in a little place called Canada, which ranges from a Marine climate to the North Pole.

Leaving out the coasts, that means a cold to very cold climate. In that case, meeting IECC 2012 standards for zones 6-8 (Table Below) would be a practical target for retrofits.

High-density fiberglass batts (R-15) plus 2" XPS (R-10) would do the trick. And with all the finishes off, getting busy with acoustic caulking and handheld foam spray at all joints and built-up posts and the like would do wonders in tightening the envelope.

This post was edited by worthy on Wed, Aug 7, 13 at 18:17

RE: Insulation in 2x4 walls

Thanks guys!

Yep Worthy, Saskatchewanian here, +40c to -40c, how'd ya know?

This looks great, but my window guy says the thickness will increase my costs and recomends 1.5XPS its that or custom for all windows :(. Hes is getting estimates on the window changes to me soon.

So R15 + R7.5 or pony-up more cash.

RE: Insulation in 2x4 walls

That brings the wall down to a nominal R22.5--not counting the drywall, siding and air film on either side.

Sounds fine to me!

Especially if you're heating with natural gas, the price of which has been plummeting with the expansion of fracking--from C$6.16mcf in 2007 to C$2.315 a couple of days ago.

Before settling on window choices, you might want to consult this Natural Resources Canada site rating Canadian windows according to Energy Star criteria. At the least, stick to windows rated for your climate zone.

(I am psychic. And your profile is public.)

BTW, this Torontonian many years ago spent a couple of summers in Saskatchewan--from remote Hudson Bay and Carrot River in the north, to beautiful Saskatoon, to Prince Albert, the city of jails and tough guys, to Regina.

RE: Insulation in 2x4 walls

Reading about dew point and foam shrinkage was enough for me to invest in a second layer of foam. Its Dow claate 1.4 inch so 2.8 will get rid of dew point issue and stagering will help with shrinkage... If the newer foam does shrink much.

I'm from PA... at least we are close to the lakes.

Thanks Worthy, you are a boon to Gardenweb.

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