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Basement insulation 1 inch EPS + Certainteed Membrain

D Tang | Posted in General Questions on

Hi all,

Trying to churn out zone 6 (Markham Ontario, Canada) basement insulation plan

* 1 inch EPS GPS foam
*  certainteed membrain ( needed?)
*  2 * 4 walls 16 OC

I know 1 1/2” or 2” EPS foam is better with higher R value, but I think this stackup should be Ok, your thoughts?


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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi D.

    Insulating a basement wall is typically a cost effective upgrade. So, why short change the project with only 1 inch of GPS, which I believe is only around R-5? Current International Energy Codes call for R-15 continuous insulation in Climate Zone 6. I'm not sure what the Canadian Code calls for. I'd consider thicker rigid foam or cavity insulation in the stud walls.

    Some builders use fiberglass and cellulose in basement stud walls, others are strongly opposed. I think that decision should be made depending on the basement and the risk of moisture and water events.

    Also, you don't need the vapor retarder. Air seal the rigid foam well with caulks or sealants around the perimeter and taped seams to prevent conditioned indoor air from reaching the potentially cool concrete walls, but the GPS and drywall will provide all the vapor protection you need.

    You may find this helpful: How to Insulate a Basement Wall

  2. Steve Knapp CZ 3A Georgia | | #2

    Also check into reclaimed rigid foam. I saw a listing in your area with 2-inch foam starting at $1.25 (Canadian) per square foot.

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