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Old 01-11-2010, 09:14 PM   #1
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new bathroom in basement

I have a partially finished basement in a 50year old house, I am putting in a bathroom. The walls are poured concrete with sill plate and wood framing on top. The walls appear to be waterproofed and painted. I do not have issues with water leakage or anything. One side of the new bathroom will be 2x4 framing along the concrete wall. Should I insulate this space along the concrete wall? Should I use a vapor barrier? I have worked in houses with finished basements with vapor barrier behind drywall, and they were moldy, very moldy. Any suggestions?


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Old 01-11-2010, 11:10 PM   #2
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also, about the floor

I also plan on putting down ceramic or porcelain tile on the concrete floor, do I need to seal the concrete first?


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Old 01-15-2010, 03:28 PM   #3
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Some Help

I'm currently remodeling my basement and here is what I have learned:


I would put polystryene foam board on the walls, it acts as a vapor barrier and insulate as well. The thickness of the foam board determines the insulating value (R value). I live in southern illinois and am using 3/4" on my foundation walls (biggest I had access to that still had a t&groove for better interlocking) Use a house wrap tape (Tyvek tape) on the seams where the foam board meets. Now you could put fiberglass batting in b/w the studs for even better comfort and with no worry about mold issues.

It would not hurt to seal it. I had to lay down some self leveling concrete. So I'd say make sure your floor is level before you seal it, otherwise you'll seal it 2x.
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Old 01-15-2010, 04:07 PM   #4
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Spray foam for the walls is the best way. But if too costly -- you need at least 2" rigid foam to act as a capillary break to prevent condensation from warm basement air hitting a cold basement wall. All seams to be taped and all gaps to be filled with spray foam. Then a 1/2" minimum air space between the stud wall and the foam board. fill this with kraft faced insulation batts. The sole plate must be pressure treated and use sill insulation as a capillary break under it to prevent moisture wicking into the wall cavity. No poly vapor barrier. In the summer the air moves into the room. In the winter it will move out. Any trapped moisture can dissapate in the air space provided.
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Old 01-15-2010, 05:43 PM   #5
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I agree with the others on foam, this from Building Science: This means limiting extruded polystyrene insulation to less than 1-inch thickness for walls (more than 1 inch thick and they do not breathe sufficiently) and making sure that the rigid insulation is not faced with polypropylene skins or foil facings. From:

And the craft paper facing if in a cold climate:
The greater the permeance the greater the inward drying and therefore the lower the risk of excessive moisture accumulation. However, in cold climates or buildings with high interior relative humidity during cold weather, the upper portion of a basement wall may become cold enough that a vapour permeable insulation will allow a damaging amount of outward diffusion during cold weather. A semi-permeable vapour retarder or foam or a supplemental layer exterior insulation can be used in these situations. Up to two inches of unfaced extruded polystyrene (R-10), four inches of unfaced expanded polystyrene (R-15), three inches of closed cell medium density spray polyurethane foam (R-18) and ten inches of open cell low density spray foam (R-35) meet these permeability requirements. From:

I wouldn't use an air space that may give a convective loop, lessening the value of the batts and spreading the moisture around rather than heading
directly inside if you had an air leak anywhere. You get an R-1 with 1-4" of air space. You need fire-blocking every 10 lineal feet as well as the whole top of the stud walls.
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