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Community and Q&A

Basement Finishing and Vapor Barrier

moose_head27 | Posted in General Questions on

Good afternoon, just looking to get some opinions regarding vapors barriers for concrete slabs and foundation walls. My home was constructed 10 years ago, I’ve been living in it for 2 years now and I’d like to finish the basement.

All current codes in my area (Northern Ontario, Canada) require vapor barriers on the walls and below the slab but I do not have them installed. My foundation walls consist of, waterproofing material(not sure the brand), 8 inch concrete, 2inch EPS foam and 1/2 drywall. No vapor barrier was installed. Furthermore my slab is about 3-4 inch thick, no insulation and has roughed-in plumbing for a washroom. The rough-in for the shower wasn’t poured completely with concrete for some reason and I could dig the gravel below the slab and feel there’s no vapor barrier underneath the slab.

Just looking to get some advise regarding finishing. I do have the drawing the house from the previous owner but they are poorly done and most details aren’t indicated.

My basement is dry overall, no issues with moisture and no musty basement smell. Going by current codes I need a vapor barrier but for some reason I don’t have any in my basement. I was also planning to install Dricore for a subfloor with some laminate overtop. The walls I was going to use as is which would bring me other issues as there’s no outlets on the foundation wall so I’d either have to frame a wall or dig in the foam for outlets and even then my drywall is only fastened to the foam.

Any thoughts? I would be willing to install a vapor barrier if need be, its just I don’t have any problems now without a vapor barrier so I should be fine? 


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  1. Expert Member
    Dana Dorsett | | #1

    >" My foundation walls consist of, waterproofing material(not sure the brand), 8 inch concrete, 2inch EPS foam and 1/2 drywall. No vapor barrier was installed."

    If the EPS has any facers on it, the facers are vapor barriers. If not, Type-II EPS (1.5lbs per cubic foot nominal density) comes clos e to meeting the NBC's definition of "vapour barrier" even without facers.

    As long as there is no moisture susceptible wood passing through the 2" foam layer there isn't a problem even though it's vapor permeance could be 1.5x the limit per the NBC definition. EPS is not air permeable, and neither EPS nor concrete is damaged by moisture. If you feel you MUST meet the letter of code, "vapor barrier latex" primer paint on gyprock runs about 0.5 US perms, well under the NBC limit.

    If there have been no liquid moisture seepage issues Dricor or dimple mat is overkill. A sheet of 6-mil polyethyene glued to the floor with an inch of EPS (any density) on top, with a plywood or OSB subfloor through-screwed to the slab with TapCons would probably be less expensive, and more comfortable.

    If the stairs were originally designed for retrofit finishing in mind (most houses your age were), the riser on the bottom step is higher than the rest, and able to accommodate the foam + subfloor without running into trip hazard code issues. Measure it, make sure that the total lift from the stackup doesn't violate code or you'll be re-building the stairs too. If it's close but a bit over, it's OK to back off to 1/2" plywood for a subfloor (it's not going to flex when fully supported by foam & slab) as long as the fastener requirements for any finish flooring doesn't demand thicker. It's OK to back off to 3/4" on the sheet foam too- it's more of a wintertime comfort and summertime moisture accumulation from the room air than it is an energy issue.

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