Insulation question for finishing basement

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Posted by: from Vaughan
10/18/2015 at 6:24:55 PM


We are planning to finish our basement this winter. It's currently a builder basement, which is 9ft high and has r12 blanked insulation from floor to ceiling. We obviously want to bring it up to r24. We are trying to find areas to save, and were wondering if, after the framing is done over the existing blanket insulation, if I can add r12 batts on top? I have read, and been told by some contractors this can be done, as long I create lots of slits, or try to remove as much existing vapour barrier, so as to not create a double barrier. I have had some people tell me this cannot be done.

Can anyone please validate or invalidate this for me please?


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Date/Time10/18/2015 at 10:34:16 PM

You can, but not simple sits cut in it. You must slice out sections about a foot wide. Then leave a foot wide section of the plastic. Etc.

But I strongly suggest the removal of all the billers material.

Then using PP adhesive, glue on 2" blue board insulation.

Then tuck tape all the seams properly. This now gives you a start with R-10 insulation and a great vapor barrier. Then when you frame the walls you can add another R-15 or R-20.

And do not add a vapor barrier.

This will give you ample comfort.

Hope this helps.


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Date/Time10/19/2015 at 12:43:45 PM

Carlisle, As James mentioned, yes you can ... but! Removal of the first layer of the vapour barrier is very important as you don't want any conpeting layers when dealing with the heat/moisture exchange. Remove as much of the first layer of vapour barrier and re-insulate as if it was the first and only layer you are doing, and you'll be fine.

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Carlisle in Vaughan
Date/Time10/19/2015 at 1:04:59 PM

Thanks Guys!

I have about 750 sqft of wall space... I was looking into spray foam. The quotes i got were in the 2600-3000 range. The cost to add an additional layer of r12 on top of the blanket is about $300 plus my time (labour). Is it really worth it to go with spray foam? or will I be fine with r24 of fiberglass? My goal is a warm basement!

Also, I am pretty sure if I stick with fiberglass, I will still get the rim joists spray foamed.

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Date/Time10/19/2015 at 10:03:37 PM

Sprayfoam is a nice way to go for sure, but pricey. In your application I would suggest that batt would be the way to go. There is a very high probability that once the room was complete you would never know if it was sprayfoam or batt insulation.

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Date/Time10/21/2015 at 8:37:48 AM

Insulation is not the sole factor for heat in a basement. The insulation does not make it warm nor cold. It assists to keep the temperature/air you are supplying constant. A basement with an R12 wrap insulation and proper mechanical completed (supply air runs extended to floor level and cold air returns) combined are more than comfortable.

However, if you want to increase your R-value, you can additional additional insulation, just do not add a secondary vapour barrier.

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