I'm beginning to plan to finish a basement. Currently I have bare concrete
block walls, which I obviously want to insulate and finish with wallboard,
probably greenboard (though some will recommend a concrete board). Basement
is cool and humid but has no active water entering it. Exterior of the bas
ement wall has dimpleboard, with weeping tiles at the footings, but no insu
lation. Wall is below grade to about a foot from the ceiling joists.
I'm looking at advice like this:
which says to put vapor barrier on the concrete, then furring strips, then
foamboard insulation between the furring strips, then wallboard. Cheap and
Two big questions:
(1) Vapor barrier on the concrete *behind* insulation? They have to be kidd
ing. That wall stays cool year round; moisture is going to go through the w
allboard and insulation and then condense right there on the back of the in
sulation. Can't be good. I'm thinking the vapour barrier has to go on the w
arm side of the insulation, just behind the wallboard.
(2) Where do I run electrical cables for outlets? I could cut channels in t
he foamboard but that puts the cables right close behind the drywall. Obvio
usly they could be armored or in flex conduit; is that the deal? Even then,
there isn't enough thickness to handle a standard device box. Does electri
cal have to be run surface-mount on such a wall?
Or should I plan to put (steel) 2x4 studs against the concrete wall and fil
l them with batt insulation like an above-grade wall?
All advice appreciated,
On Thursday, June 12, 2014 4:53:05 PM UTC-4, Chip C wrote:
e block walls, which I obviously want to insulate and finish with wallboard
, probably greenboard (though some will recommend a concrete board). Baseme
nt is cool and humid but has no active water entering it. Exterior of the b
asement wall has dimpleboard, with weeping tiles at the footings, but no in
sulation. Wall is below grade to about a foot from the ceiling joists.
n foamboard insulation between the furring strips, then wallboard. Cheap an
dding. That wall stays cool year round; moisture is going to go through the
wallboard and insulation and then condense right there on the back of the
insulation. Can't be good. I'm thinking the vapour barrier has to go on the
warm side of the insulation, just behind the wallboard.
I think the idea of the vapor barrier there is to keep any moisture that
might weep through from the cement block basement walls from hitting
the insulation and furring strips. It's different than where you have
a moisture barrier in an exterior above ground wall or between an uninsulat
attic and a ceiling. In those cases it can be 75F inside and 10F outside,
creating a big differential that can allow condensation. In a basement,
it's a much smaller temp difference, ie 70F basement and 55F walls, so
not nearly as much potential for water to condensed by coming out of
the basmement air. It's a lot more likely for moisture to go the other
way, coming out of the block wall. I've seen Mike Holmes do a bunch of
basements in Canada and he put the dimple type barrier product on the insid
of the basements where there were water problems, so any water, if it does
make it in, hits that and goes down to the french drain.
the foamboard but that puts the cables right close behind the drywall. Obv
iously they could be armored or in flex conduit; is that the deal? Even the
n, there isn't enough thickness to handle a standard device box. Does elect
rical have to be run surface-mount on such a wall?
Even if you ran cable, where would the boxes go? HD shows using 1" thick
strips. I'd use 2x4's leaving space for boxes and cable.
ill them with batt insulation like an above-grade wall?
Steel is an option and you don't have to worry about it rotting.
Folks have used batt insulation, but I think with regard to moisture the
rigid stuff is better, if it gets wet for some reason, it won't absorb
and hold water like batts will.
On Thursday, June 12, 2014 5:45:54 PM UTC-4, trader_4 wrote:
Here's TOH and how they do it:
And similar discussion here, with photos showing it done
Neither used a separate vapor barrier, instead relying on
the insulation board.
On the video they used 2 inch foam which is vey good. I would never want to
drill holes in cinderblock. Thick cement would be ok. I think they glued
the seams between foam boards, used no tape. Don't really need thicker foam
below freeze depth but in that system, you need a flat surface.
You could use a double vapor barrier, one against the outside wall to keep
any mooisture from coming into the insulation from wall moisture, and a sec
ond vapor barrier layer on the inside of the insulation, to keep moisture f
rom getting into the insulation from household moisture. It is belt and su
spenders, but then you've covered all the bases.
I do it like this. Put foam up against wall. The foam should have a
barrier, aluminum, or a layer of polyethylene. 1/2 inch foam ok, 1 inch
better. This is the vapor barrier. I then build a wall with 2x4 s. Add
additional loose insulation inside.
Vapor barrier on warm side no good. You will have mold. If like my model,
the foam will provide enough temperature barrier so condensation will not
happen. I'm using 3/4 inch foam on underground walls. I use tyvec tape to
join foam boards.
I'm not sure why TOH went through all of the trouble of building the grid
system. Why not just build a 2x4 wall and be done with it? Seems like it
would be a lot less work, no need to drill numerous 5” deep holes into the
concrete wall, no hammering of anchors that have to be more expensive than
the nails or screws required to build the wall, etc.
What am I missing?
On Friday, June 13, 2014 1:23:36 PM UTC-4, DerbyDad03 wrote:
IDK that you're missing anything and I agree with what you're saying.
The holes are only about 2" deep in the actual concrete, but still
drilling into concrete wouldn't be my first choice either. I put those
links up more with regard to ideas on the insulation and vapor barrier
issue which applies regardless of exactly how you build it. Doing
the furring strip approach makes even less sense if you need the depth
for electric, because then Tom tells you to nail more strips perpendicular
to build it out even more, which is yet more work.....
Usually he's has great ideas, but I agree, this time, if it were me,
I'd just use 2x4's. Probably easiest to frame it out on the floor,
then stand it up, shim it in, and nail it in place. I think one of
those videos suggested using composite on the floor before the bottom
plate. I think that's a good idea for moisture separation too.
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