# Insulating Basement Walls in a Duplex



## Windows on Wash (Aug 30, 2011)

No need for foam on the common wall. I would insulated it though, the entire wall with fibrous insulation, and pull out stud wall out from contact to help with the sound transmission. 

Cut around them as best as possible and seal up with spray foam. 

Best to fill the gap so there is no cold spot. Be sure to use a closed cell and low expansion foam. 

Fill the cavities as well.


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## AllanJ (Nov 24, 2007)

Seal the edges of the foam board(s) to the concrete wall as best as you can.

You could have continuous large sheets of foam stopping a few inches shy of the brackets on top to facilitate attachment to the wall getting a good seal. Then you can glue on small pieces to fill the remaining space. 

To prevent freezing of the pipe, there should be no insulation between the pipe itself and the finished interior wall.


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## Windows on Wash (Aug 30, 2011)

Being that it's a drain pipe, there shouldn't be any fluids or solids sitting in the pipe.


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## jplus281 (Nov 17, 2015)

Thank you for the replies and info! So, on that non-exterior foundation wall should I use some poly sheeting against the wall before putting in the fibrous insulation so that the insulation doesn't actually touch the concrete or is that not necessary?


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## Windows on Wash (Aug 30, 2011)

There shouldn't be any water in that wall. Use mineral wool either way. Seems to be less moisture sensitive.


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