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delly_gw

Using less than 2' XPS in my basement

Delly
12 years ago

I have already purchased some batt isulation for my basement (R14), and then was doing some research and was wondering if I could use 1/2" Dow Cladmate directly on the concre walls, then 2x4 stud, and then fill in the stud cavity with the R14 batt insulation?

I was then going to put a vapour barrier over the studs and drywall.

Would this be acceptable?

Thanks

Comments (4)

  • worthy
    12 years ago

    Not unless you're on southern Vancouver Island, which is a Marine climate.

    Hygro thermal Regions of North AmericaSource: Building Science Corp.

    In most of the rest of the country--cold and very cold--at least one-inch extruded (XPS)would be satisfactory, followed by fibrous insulation. The vapour barrier is not necessary, but according to Building Science won't be detrimental if building inspectors insist on it.

  • Delly
    Original Author
    12 years ago

    Thanks for the response.
    I'm in the "Cold" region. The builders put 2 rows of 4' blanket insulation directly on the concrete walls (pretty much floor to ceiling). The insulation in these blankets is contacting the concrete directly.
    From everything I've heard and read, this is not a good idea.
    So, as suggested, I'm thinking I'll take it all down and put 1 to 1 1/2" XPS on the concrete, stud the wall and fill the cavity with fibrous insulation and then drywall.

    What do you think of that configuration?

    2 Questions to confirm my process:
    1) When I frame the wall in front of the XPS, do I frame right against the XPS or leave a gap (I'll be adding batt insulation in between the studs).
    2) Since I'm using the 1" to 1 1/2" XPS, I'm debating whether or not to put vapour barrier between the studs and the drywall. The vapour barrier is relatively inexpensive and fairly easy to install with 2 people... is there any benefit to it aside from the inspectors preference?

    Thanks

  • worthy
    12 years ago

    1 to 1 1/2" XPS on the concrete, stud the wall and fill the cavity with fibrous insulation and then drywall.

    Fine.

    Place the framing against the extruded polyurethane boards (XPS). A vapour barrier is absolutely not needed. If there's still some inspector somewhere who is asking for it, you can always (politely) show them the Building Science Corp. publications.

    The leakiest parts of the basement are the abovegrade spaces between the joists and the intersection of the rim (mud sill) and the concrete. You can foam all the space with do-it-yourself polyurethane spray or use XPS between the joists and caulking and small cans of polyurethane spray (Great Stuff etc.) for all the other gaps.

    Here is a link that might be useful: Building Science Corp on Basements

  • Delly
    Original Author
    12 years ago

    Thanks for the assistance worthy.