Insulating Basement How dDo I handle Ceiling Joists?

[mkochsch]

OK I'm ready to frame and insulate my unfinished basement. It's about two-thirds below grade. It's dry. I live in one of North America's colder regions -- nearly smack in the centre in Canada. I'm going to use two-by-fours stud walls set slightly away from the concrete wall to accommodate extra insulation (going for R24). I'm going to vapour barrier with Tyvek on the warm side between the studs and the drywall instead of on the cold side. I'm planning on putting the insulation-barrier-drywall layer right up to the two-by-ten ceiling joists. How do I, or do I put barrier and insulation between the joists agaist the concrete. It seems to me that the whole point of doing a barrier is to have a continuous membrane to hold in the moist air in the house. By the looks of it if I do go between the joists that still doesn't make the barrier continuous to the main floor above the basement. I was thinking of finishing the ceiling of the basement with ceiling tile and possibly stuffing even more insulation between the joists to further isolate the basement environment from the floor above it. Is this OK to do?

[edee em]

There is no need to insulate and vapour barrier warm side to warm side (ie basement ceiling and first floor floor). Some even speak against insulating a basement ceiling as warm air rises to warm first floor, etc. I did insulate some rooms for soundproofing, not insulation value.

As to the rim joist space, I spent a lot of time insulating the space with styrofoam. Cut the piece to fit in snugly, apply generous beads of caulking all around and push the foam into place. I even came back and caulk the foam again from the outside (waste of time and money, but good for the "I'll never have to worry about that"). This allowed me to run my vapour barrier up to the top plate of the wall and onto the ceiling joists about 3-5 inches. Using the foam, which itself is a vapour barrier, allowed me to not worry about running my vapour barrier into the cavity.

Good luck

[SofaKing]

I wasn't planning on putter barrier on the ceiling, I was thinking of just insulation so the first floor was a little warmer if I chose to keep the basement a little cooler when not in use. I was more concerned about the space between the top of the basement wall around the sill area. I see now that since my house is ~ 40 years old and does not classify as "super insulated" I'll never achieve a continuous membrane from the first floor to the basement. I think your plan about building it up with rigid foam sounds and caulking sound reasonable. I'll mull that over for a bit. Thx.

[SofaKing]

BTW to avoid confusion sofaking = mkochsch I just answered from a different computer with a different profile.

[Joe]

I'm in the process of doing a similar thing in the rim/joist space.

1. painted the whole box shaped area with a latex primer, just to make me feel better. Put two coats on the bottom of the floor above, hoping this would act as a vapour retarder.
2. sealed every possible place with caulking. It was drafty up there.
3. put a layer of 2 inch XPS on top of the concrete block up to the level of the sill.
4. put in 5 1/2 inch rock wool, very easy to cut. This left me with

1/2 inch of what I figured was too much space. So 1/2 inch XPS went in next.

1. put in a large rectangular piece (well about 10in x 12 in) of 2 inch XPS. finally sealed everything with caulking.
2. I believe XPS has to be covered with something so I'll put 1/2 inch plywood over it.

That's a lot of work for a little spot, but stopping drafts and adding insulation has got to be a good thing.

Joe Eastern Ontario

On Sun, 22 Feb 2004 16:46:46 GMT, "SofaKing" wrote: I think your plan about building it up with rigid foam sounds

...

[Steve Nekias]

You will want to download a 144page brochure from the Natural Resources Canada, Dept. of Energy Efficiency called "Insulating Basements, Crawl Spaces, and Slabs-on-grade." Here is the link:

If you have problems, go to click on the "Home Renovations" tab, then look for a PDF format file with that title.

Be careful if your house has joists set on direct contact with concrete or concrete blocks--they indicate that there is a problem with wood rotting if you insulate the rim joist area!

Mr Fixit eh

[SofaKing]

thankyou that's what I need to read.

[SofaKing]

Yes. My floor joists are indeed set into the concrete. Hmm.

[Steve Nekias]

Moisture can wick into the concrete from either the ground, or from brick sheathing-if there is no flashing.

Apparently, the problem is that insulation in the rimjoist area reduces airflow that would dry out any moisture that might get into this area, and of course, untreated wood doesn't get along well with concrete plus moisture.

NRC recommends that you caulk the area well with accoustical sealant to eliminate airflow (that will provide significant energy efficiency improvement). You will find detailed instructions on pages 65, 71, 74 (see last thread)dealing with joists-in-concrete.

The recommendation is to caulk the seam at the top of the header (between header and subfloor), and at the bottom of the header (between header and concrete foundation); then caulk the seam where the floor joist meets the header, and around the joist where it is imbedded in the concrete--whew!

Mr Fixit eh