Thoughts on this basement wall assembly


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Old 06-30-15, 01:36 PM
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Thoughts on this basement wall assembly

I'm doing a basement reno in southern, BC, Canada. We are climate zone 6 here and it doesn't get too humid. Average daily January temp is about 20F and average daily July temp is about 65F. During the past winter, the humidity in my basement never got above 35%, and was usually closer to 30%. In summer, it might hit 50% on the warmest days.

I want the basement to be comfortable, and currently its a bit cold with only an R12 fibreglass batt in the outside walls. The entire foundation is pretty much below grade. My planned wall assembly from the inside out is as follows:

- latex paint (class III vapor retarder)
- 1/2" gypsum drywall
- 2x4 studwall with R14 Roxull mineral wool between the studs
- 1 1/2" of EPS glued to concrete (Durofoam Class II vapor retarder at 0.5 perm/inch, R value of 3.75/inch)
- poured concrete foundation

You will notice I did not include a sheet of poly behind the drywall as my understanding is that would be a recipe for disaster with EPS in the wall being a low permeance material. I plan to insulate the floors too with Dricore R+ tiles.

I know a lot of others have used the rigid foam and batt approach for basement walls before, so before I forge ahead I wanted to ask if anyone has any tips or warnings on my plan. Thanks.
 
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Old 06-30-15, 01:49 PM
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The use of Roxul does not require a vapor barrier, so eliminating that is fine. Be sure to tape all the seams of the EPS.
 
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Old 06-30-15, 02:07 PM
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Yes, I will tape the EPS seams for sure. I'll also seal the tops and bottoms with either caulking or spray foam. This particular type of EPS is foil faced and popular around here for exterior use over sheathing, but the manufacturer claims it is equally appropriate for use on the interior (or exterior) of basement walls. Ideally I would use 2" or more, but got a great deal on some 1 1/2", so in my case I think it will be good enough.
 
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Old 07-02-15, 04:17 AM
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Do you have any idea what the characteristics are of the backfill material outside the foundation?

Insulating is a great idea but sometimes overdoing it can allow frost to act on the exterior and develop heaving issues. The exterior should not be heavy clay bearing soil directly against the foundation.

I certainly advocate the insulation, just advising you to be cognizant of the myriad of issues that typically are involved in construction projects.
 
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Old 07-02-15, 06:26 PM
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Soil outside the foundation is good, not much clay. There were a couple small cracks in the foundation that I filled with a polyurethane injection kit.
 
 

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