Page 1 of 1

Varying XPS Rigid Foam thickness

Posted: Thu Jan 24, 2019 8:58 pm
by WillLee
Hi Shannon,

I've got to say this is a great website I've just discovered! I've searched the forums and read up a lot and I'm really impressed. I also like that we share similar climate (I'm also in Canada). I just bought a house with an unfinished basement, however the framed studs along the concrete wall are there as well as some R12 fiberglass batt insulation along the top half of basement wall. The spacing between the studs and the concrete wall varies between 1.25inches to 2.5 inches.

My plan is to rigid foam up against the concrete, seal with tuck tape and Great Stuff spray foam, put down some batts floor to ceiling, and then drywall. No vapor barrier.

What I was wondering was:
1. With the varying space between stud and concrete wall, will it create an issue if I use different thicknesses of rigid foam throughout the basement? I was thinking it would be fine if I ensured the tucktape was wide enough and used spray foam when needed.

2. The cement wall has bumps sticking out about 5mm or so all along the basement walls. I don't know the name of it, but it is a result of the method of pouring the cement walls. Can I get away with ignoring these bumps and not have my rigid foam flush against the wall?

3. The basement walls currently have a poly vapor barrier, fiberglass batts, then a black fabric up against the concrete wall. Am I removing all 3 before to place the rigid foam up, or can I leave the black fabric. My home was built in 2002 if that helps in deciphering what this black fabric is.

Thank you so much for any suggestions or info you may have.

Re: Varying XPS Rigid Foam thickness

Posted: Fri Jan 25, 2019 7:36 am
by Shannon
Welcome to the forum.

First off unless you have 2" foam everywhere you will need a vapour barrier. So i would use either 1" or 1-1/2" foam everywhere and Roxul R14 in the wall cavity. Then a vapour barrier and drywall over that.

The tie hole bumps left behind should be no problem, if you get some that stick out more just use a cold chisel and hammer to knock them off.

I would think the "black fabric" is maybe Typar house wrap hung back wards? does not really matter if you are adding foam that should be removed anyways.

Re: Varying XPS Rigid Foam thickness

Posted: Fri Jan 25, 2019 10:13 pm
by WillLee
Sounds good.

Seeing how I already have some R12 Fiberglass batts in the top half wall of my basement, should I rip those all out and replace with R14 Roxul?

If so, can I toss those batts into the attic for more insulation? My attic currently has the little fiberglass chunks everywhere.

Re: Varying XPS Rigid Foam thickness

Posted: Fri Jan 25, 2019 10:16 pm
by WillLee
Oh and I guess I might as well ask this question while I'm here:

I've read that you most often use Dricore as a subflooring. Do you find Dricore R+ does enough to prevent a humid basement in the summer? I've seen talk of the T&G of the Dricore doesn't provide enough of a barrier to the OSB in the Dricore.

Re: Varying XPS Rigid Foam thickness

Posted: Fri Jan 25, 2019 10:55 pm
by Shannon
Using the r12 will be fine if you wanna use it up or you can place it the attic if you want.

I have not personally used the Dricore R+ but have used the standard dricore many times and have it in half of my basement. I can’t say I have a humidity problem at all.