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Basement insulation for concrete party wall

phillydude | Posted in General Questions on

Hi All,
I’m noobie DIYer as far as framing and finishing basements go, trying to start a project to finish my 500 sq. ft. basement in southeast Pennsylvania. I’m in a end unit town home, so the basement has poured concrete external walls on 3 sides, and a concrete party wall shared with my neighbor. Need advice and confirmation on my insulation plans, any help would be appreciated!
I plan to frame the wall with a 1.5″ gap between the concrete walls and frame. For the exterior walls I am planning to go with 1.5″ closed cell spray foam and filling the cavities with Roxul, based on all the reading seems like that’s the best way to avoid moisture issues and get good R value. Do I need to worry about moisture issues with the concrete party wall? I did not want to spray foam that wall to save money and also to soundproof between the 2 walls (foam would couple the walls) as I will setup my home theater in the basement and don’t want sound traveling through the shared wall. Can I just use Roxul safe n sound or will that have moisture issues? If so, I was thinking of applying 0.5″ or 1″ XPS rigid foam boards and leaving a 0.5-1″ gap between the foam board and wall frame to decouple the two.
Any suggestions or ideas?


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  1. GBA Editor
    Martin Holladay | | #1

    Philly Dude,
    I'm assuming that your basement shows no signs of water entry. (That's always a prerequisite for any basement that needs interior insulation.) If there are no existing problems with water entry or dampness, you can insulate the party wall with Roxul, and skip the spray foam on that side.

  2. phillydude | | #2

    Thanks Martin! No moisture issues or water seen in the 5 years I have lived here... I do need a dehumidifier in summer, otherwise it smells musty.
    So would it be worth using 0.5" or 1" XPS on the party wall or is that unnecessary and waste?
    Also, is 1.5" CC Spray foam sufficient or is 2" strongly recommended with Roxul in between the studs?

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