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?
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.
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.
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
5. put in a large rectangular piece (well about 10in x 12 in) of 2
inch XPS. finally sealed everything with caulking.
6. 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.
On Sun, 22 Feb 2004 16:46:46 GMT, "SofaKing"
I think your plan about building it up with rigid foam sounds
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 http://oee.nrcan.gc.ca , 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
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
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