I’m south of Boston (cold in winter) and in the process of finishing my basement according the FHB article / Building Sciences method (http://www.taunton.com/finehomebuilding/PDF/Protected/021169078.pdf)
Here’s my question: rather than apply foam directly to the rim joist, can I run my 2″ Dow XPS from the floor all the way to the ceiling, i.e. to the bottom of the first-level floor? I would run it between the floor joists and seal all gaps in that fitted area with foam and Tyvek tape – basically, a 96″ floor to ceiling run right up past the internal foundation wall with cutouts to accommodate joists. The reason for this is two-fold: 1) it’s more straightforward, i.e. I don’t have to work around utilities to get back into the joist area; 2) I have this design approved by the building inspector, because it shows a *continuous* vapor retarder (the foam has a perm rating of 1.0 per inch).
The cold joist is still protected from the warm air I will create in the basement space in winter, but there would be a 12″ pocket between the joist and the edge of the foam (which I can stuff with existing fiberglass). Is this OK?
Thoughts?
BTW, this is a re-post from another thread, where I think I caught the topic too late in the conversation to generate responses. Thanks.
Replies
Greetings adclay,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
I've talen a few courses on energy efficient houseing, and was taught a similar detail. We use styrofoam to air seal the joist spaces. Stuff with fiberglass as you mentioned, then rigid foam, sealed with foam in a can around the edges.
Lately been using this on ICF basements, so the foam is sealed to the inside top of the ICF, the joists and the subfloor. Then the first floor a/vb is caulked to the subfloor with accoustical caulk. Seems it would give an airtight joint, but have not tested with a blower door.
I think your version sounds fine.
Great to hear - thank you.
Sorry for the delay - I don't hang out here much any more. The thing I don't like about your detail is that it doesn't isolate the end of the joist bay from the top of the foundation, so I can imagine a moisture build up. I did say imagine, and it could be I'm paranoid. Which, with un-inspectible spaces, isn't a bad trait.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Book of Merlin
Andy - thanks. The uninspected space isn't ideal I know; that said, I have sealed off the joist area very tightly with XPS and foam spray around the edges, so the warm air can't come in contact with what's behind it and cold. Believe it or not, I even put 2" XPS over the top of the foundation, behind the vertical face of my floor-to-ceiling XPS to keep the entire foundation from coming in contact with cold air. Again, I realize it's not ideal, but I believe I have have come as close to the intent of the Building Sciences method as is possible. Don't know if that changes anything for you?
It sounds like you thought the details through. I'd guess you'll be fine.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Book of Merlin
Andy,
Noticed the lack of poly VB under the slab, is that not a code requirement? If in fact there was a VB under the slab couldn't you eliminate the EPS and use 1x3 sleepers (16" O.C.)to the slab with 3/4" T&G ply as your subfloor?
Geoff
A sub slab VB is indeed required, but only for the last twenty years or so.
Sure, you could use sleepers and so forth if you know there's a vb. However, I've seen enough concrete guys slash them and pull them back to facilitate drainage when they place the slab that I don't really trust them to be in one piece.
There be hacks everywhere. Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Book of Merlin