Basement Remodel

gabel8 · 05-24-2011, 09:21 AM

I live in Pittsburgh, PA and I am currently in the plannign phase of finishing my basement. I am going to be doing it myself. I have read a few books and got references online and I am torn for one phase. I am leaning towards using 2" rigid foam for my basement walls but it seems some of the sources I've seen use this technique and some don't. I've also talked to a few of my neighbors that didn't use the rigid foam. I was hoping someone could explain to me the advantages/disadvantages of using the rigid foam and is it really needed? I'm really torn as to which way to go. If I don't use the rigid foam, what is the best way to use for a moisture barrier then.

Rory Read · 05-24-2011, 10:02 AM

Gabe,

I like to use rigid XPS foam on basement walls but usually only install 1" thick sheets. We often then frame on the interior side of the foam and install standard fiberglass batt insulation in the new bays. (Note no vapor barrier on the interior of the wall assembly.)

The price is right, if you use tongue and groove, it can be fitted quite tightly together and to the floor very quickly, is a good vapor barrier/retarder, and is extremely moisture resistant.

I don't think I have heard or read any arguments claiming batt insulation alone would be a better option. There are superior but more expensive ways to go such as spray foams or pre-built basement wall systems, but there is almost always a cost/benefit decision for every client, and you have to decide what is reasonable for you.

I see that you have been doing your homework, but have you read the Building Science articles on basements?

Follow up questions to you from a contractor would be: how wet/dry is your basement, are you insulating the floor or the basement ceiling, what are the foundations walls like, i.e. straight or smooth, will they hold fasteners, how much basement wall is below and above grade, and are your framing or planning on attaching wall board straight to the XPS?

Have fun with it.

Rory

gabel8 · 05-24-2011, 10:10 AM

Rory,
Thanks for the information. So do you think 2" is overkill and 1" would be sufficient? Also, is there a brand that you prefer between Dow and Owens Corning?

Thanks.

Rory Read · 05-24-2011, 02:19 PM

2" might not be overkill for you. Note that for foundation walls above grade, you would probably need 2" or more if you want to install a vapor barrier (such as rigid foam insulation) on the exterior side of the cavity. That gets into a different topic though. Above or below grade, wall assemblies should be designed to the local climate. Try Building Science Corporation and Building America for information specific to where you live.

I think that the products are identical, although there are different specifications that only become relevant when it's going under a floor system. I haven't found thicker T&G though. If I buy from a masonry supplier such as White Cap, I can buy 2" square edge for less than 2 pieces of 1" T&G from a box store. However, if I was trying to build a very tight assembly, two layers of T&G with a staggered overlap would be a very strong performer.

Cheers,

R