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Community and Q&A

Basement foam insulation

Seb L | Posted in Energy Efficiency and Durability on


I’m new to GBA and have been doing a lot of reading. Great website for information! I am currently in the process of finishing my basement. I live in Edmonton, Alberta, Canada. I’m not sure what climate zone it is, but it’s very cold! House was built in 2007. I have been working hard to air seal it to make it more energy efficient. 

Currently, my basement has a standard frost wall from the builder which consists of 2×4 steel stud framing with R19 fibreglass insulation and a 7mm poly vapour barrier. 

I am going to remove the steel stud framing, and install Halo Interra, 2” think foam board to the cement walls. Then I will reinstall the steel stud framing and the fibreglass insulation batts. 

I am looking for some feedback on my plan. The Halo Interra product says it acts as a vapour barrier. I am going to install the foam board and tape in between the joints with Siga Sicrall. As for the bottom, I am planning to seal the foam board to the slab with Siga Rissan using the dockskin primer. Any other sealing will be done with handi foam spray foam. Since this product is a vapour barrier, once I reinstall my steel studs and fibreglass Batts, do I need to install and polyethylene?  I would like to avoid it if possible, but I want to make sure what I am doing will not cause any moisture issues. Additionally, I do have an issue as there are two sections of my basement that already have fibreglass / vapour barrier installed that I cannot easily access (without significant effort)  I am thinking to tape the existing vapour barrier to the foam board I am installing to keep the vapour barrier consistent  could anyone provide some feedback on this?

As for my rim joists, I  going to cut the Halo Interra into pieces and install them in the rim joists. Gaps will be sealed using handi foam spray foam. I will then reinstall the fibreglass batts that are in there now to further increase my r value. Is this an adequate way to air seal my rim joists?

Lastly, all my windows are double pane windows, but I am certain the gaps were just stuffed with fibreglass. My plan is to remove the trim and fibreglass, spray foam the gaps with handi foam windows and doors, then use Siga Fentrim IS20 to further air seal. Is this a good method to improve my air sealing around my windows? Currently I have quite a bit of condensation, frost and mold around all my windows. I am thinking because they are not air sealed properly, the cold outside air is making the windows cooler on the inside, causing increased condensation. Once the air sealing is completed, will this increase the interior temperature to reduce the amount of condensation I am getting? Please note that I installed a HRV (simplified installation) last year to help keep the air fresh and increase the frequency of my air exchanges. Although it has helped, I am still having condensation issues, even when my interior humidity is in the low 20%. We always run the bathroom fans when showering, but it does not fix the condensation issues.

Any and all feedback is greatly appreciated. 

Thank you,


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  1. Expert Member
    Rick Evans | | #1

    Sebastian, Welcome to GBA!

    I think you are down a great path here and you have clearly done your homework!

    Im no pro myself, but I'll share a couple of thoughts regarding your basement insulation plan:

    1. Once you add the foil-faced foam board, you should avoid adding the layer of poly. It is not needed and will only cause trouble if anything leaks through the foam board.

    2. Steel is 400x more conductive than wood. Fitting fiberglass batts between steel studs lowers the effective R-Value of that wall by 70% or more. I would use the steel studs for interior walls if you ever finish the basement or sell them online. Then buy some lumber and rebuild those walls with the fiberglass batts filling the stud cavities.

    3. Even cheap tapes (like Canadian Tuck Tape) work well with foil faced insulation. You probably don't need the fancy Swiss tape for this application. However, you may need it for sealing the foam board to the concrete slab, as you stated. A good caulk would work well too.


    This sounds like a big project but your plan might work. If you are getting moisture issues AROUND the window then I really like your plan. Keep the air sealing on the interior and not the exterior. In an extreme climate like yours, only the best windows might prevent condensation on the window itself on cold days. If you are keeping humidity down in the house as you described, then condensation on the glass may just be something you have to deal with?

    Good luck enjoy the project!

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Sebastian.

    Everything you are planning to do makes sense to me. I don't believe that you need a vapor retarder over the studs in your basement walls. Do an impeccable air sealing the rigid foam. You may find this article helpful, if you haven't seen it already: How to Insulate a Basement Wall.

    As far as the windows go, Try air sealing them. However, if your indoor RH is as low as you say, and if the condensation if forming on the glass throughout the house, it may simply be that the glazing isn't insulated well enough for your cold winters. After trying the air sealing work around a few windows, you'll know.

    1. Seb L | | #3

      Thank you both for your reply.

      For the window air sealing, would you recommend both foam and tape? Or just one or the other? Would you leave the fibreglass in or remove it?

      Thanks again!

      1. Expert Member
        Rick Evans | | #4

        Its tedious work, but I would foam it carefully with low expanding foam and then tape it. I'd also try to remove the fiberglass as much as you can.

        Spray foam can get messy- it may be worth covering each window with paper before applying the foam.

        1. Seb L | | #5


          One more question for everyone. There are a few existing sections in the basement that have the standard frost wall built already with steel stud framing l, batt insulation, vapour barrier and drywall (behind the stairs) which are not feasible to disassemble. The cost and complexity of this work would just be too great. Is it possible to foam board up to these sections and tie the vapour barrier into the new foam board I put in for a continuous vapour barrier?

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