Vapour Barrier with Rigid Foam in Basement

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Posted by: from Stouffville
8/25/2013 at 12:15:01 PM


I was wondering about whether vapour barrier is required under the following scenario:

- we removed current 1/2 wall coverage of drywall and insulation

- on basement walls we applied a mould and mildew resistant waterproofing paint meant for concrete walls

- we applied 2" thick rigid foam, floor to ceiling, current R value of 10

- after getting a professional in to do framing, we plan on putting in batt insulation to meet/exceed R20, which I understand is the minimum R value in ontario

So my question is, prior to drywalling, would a vapour barrier be required, if we already have rigid foam in place?

Thanks, and any other advice would be greatly appreciated.

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Quality Homes Saskatoon in Waterhen Lake
Date/Time8/25/2013 at 2:24:29 PM

There would be no vapour barrier necessary, just seal the penetrations on the exterior wall with caulking and spray foam where ever there is a breach and you are good to drywall over it.

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Date/Time8/25/2013 at 2:51:28 PM

Use Tuck Tape on all of your joints in the ridged board. And use spray foam in all penetrations or holes, such as gas lines, vents etc. Sparay some expandable foam in the area between the first floor floor joists as well. If they have not been filled with ridged board insulation. Then you are good to go.

Enjoy your new basement area.

James Fram

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Date/Time8/25/2013 at 8:02:30 PM

Hi. I am sure you will get a variety of opinions on your question.

I will say yes, you need to install vapour barrier for the following reasons:

Vapour barrier is installed to reduce the amount of moisture transmission from the warm room through the drywall finish and then condensing into water droplets toward the cold exterior portion of the wall. Because you are installing batt insulation over the rigid foam, the batt insulation is susceptible to moisture damage. Also, if you are using wooden studs, they too are susceptible to moisture damage.

If you were using rigid foam board alone, you may be able to eliminate the vapour barrier, provided warm air cannot leak between the foam board into the cold wall behind. (seal joints with tuck tape). Even with the foam board alone, there is still the possibility that wooden framing would become damaged by the same process if they are not protected with the vapour barrier.

Remember, warm always moves to cold. As soon as warm air hits cold air, it condenses. Once batt insulation becomes wet, it loses its effectiveness as an insulator, and mold will grow.

Hope this helps.

Tony Vetere and Sons Construction

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Date/Time8/25/2013 at 10:24:27 PM

Dan, I would go with Toni's recommendation. It "may not be necessary" but for the cost difference, it would save you in the long run.

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Date/Time8/27/2013 at 5:36:23 AM

You need a vapour barrier on the WARMEST side, meaning over top of the batt insulation and is required. If you tuck tape the ridgid insulation only, you could have moisture build up on the batt insulation. If you tuck tape the ridgid insulation AND put a vapour barrier over the batt insulation, you could be trapping moisture in between the two layers.

Vapour barrier is cheap and really fast and easy to install.

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Dave from 360renos in Navan
Date/Time8/28/2013 at 7:47:07 AM

Good morning Dan

If you used EPS rigid foam you do NOT need a vapour barrier as long as all the board seams are taped and caulked. Was acoustic caulking applied at the seam of the foam board where it meets the concrete floor and at the top near the header? You want zero movement of air behind the board. You don't want any warm air getting through to the concrete wall.

Yes, R20 is the new code for basement wall insulation

Here is some reading of the best practices in Ontario for finishing your basement properly


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