Basement insulation - adjoining walls

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sebastien
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Joined: Sat Oct 26, 2019 7:15 pm
Location: Montreal, Canada

Basement insulation - adjoining walls

Post by sebastien » Wed Jan 01, 2020 9:46 pm

I have a duplex in the city with an unfinished basement.
The basement is poured concrete - same as both my adjoining neighbours.

I want to finish the basement to turn it into livable space. And one of the steps is insulation. Everything I find online is about insulating fully detached house basements - this isn't my case.

Do adjoining basement walls need to be insulated (i.e. vapor barrier, rigid foam, etc)? Or would it be sufficient to just do so for the exterior facing walls?


thanks! :D

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A. Spruce
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Re: Basement insulation - adjoining walls

Post by A. Spruce » Wed Jan 01, 2020 10:05 pm

If it's a concrete wall between you and neighbor, I'd insulate to help regulate the temperature more evenly. Concrete is a heat sink, meaning it absorbs heat, so if you don't insulate, it will be hard to keep the temp comfortable/affordable.

If the wall between you and neighbor is a framed wall, I'd insulate and double the drywall. The more mass the wall has, the less sound will carry through the wall. Insulating the cavity keeps acoustic sounds (voices, light music) down. Mass stops reverberation down (sub woofers on stereos/tvs, impact noises like drums). If you think noise will be an issue, then I'd go to the added effort of using decoupling track between the two layers of drywall.
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Shannon
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Re: Basement insulation - adjoining walls

Post by Shannon » Thu Jan 02, 2020 6:03 am

For a concrete wall dividing you from the neighbour I would do a couple of things different. first if you are in a cold region I would use the foam on the dividing wall but only about 8' in from the exterior ends if you want to save a bit of cash. But I would use the batt insulation in the entire thing. As for the air/vapour barrier it should be on exterior portions only so it can pass across the exterior wall portions of the home and through the wall and be sealed to the dividing concrete wall. The easiest way is to install the foam on the exterior wall and and before you attach the next foam sheet on the concrete adjoining wall attach/seal a 16" strip of poly to the concrete so it will pass between the two foam sheets and be long enough to pass through the framing corner. It can then be sealed to the main air /vapour barrier once it is installed. Its kinda a tricky piece to get sealed well before hand but worth the time.
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sebastien
Posts: 7
Joined: Sat Oct 26, 2019 7:15 pm
Location: Montreal, Canada

Re: Basement insulation - adjoining walls

Post by sebastien » Thu Jan 02, 2020 7:25 am

These recommendations make a lot of sense.

Thanks, guys!