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Community and Q&A

Batt placement in basement wall

carlosdanger | Posted in Energy Efficiency and Durability on

I’m about to finish insulating my basement which I have already insulated with 2 inches of foam against the block foundation from the top to the bottom. I was planning on also installing rockwool in the stud bays. However, one of the stud walls is 4″ off the foundation and I wasn’t sure how to insulate this. Should I fill the whole gap and studs with insulation? Just the gap? Just the studs? Also, half of this wall is going to be in a finished, living area of the basement while the other half will be in a storage area. Would it be better to insulate the wall between the living area and the storage area and leave the area behind the wall in the storage area with only foam insulation or would it be better to insulate the whole length of wall in a uniform way? Thanks for any advice!

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  1. Expert Member
    Michael Maines | | #1

    Kevin, bad things happen in interstitial spaces--I recommend putting the mineral wool batts behind the studs, in contact with the foam. You could also insulate the stud bays but unless you're in a very cold location it's probably not worth the effort, from financial, comfort or carbon emissions viewpoints.

    Similarly, it's best to keep your control layers close together, so the foundation (which provides water, vapor and air control) should be the location of the thermal control layer as well.

  2. carlosdanger | | #2

    Thank you for your response. My house was built in the 1930s so the floor is definitely a weak point in terms of insulation and moisture control. I don't have much headroom as it is, so adding insulation is not really an option. I was planning on putting in a floating floor (possibly 100% cork for its water resistance and insulating properties ) on top of a 6mil vapor barrier. I know this is what is normally recommended but was wondering if that view is shared here. I was wondering what might happen around the edges of the vapor barrier where it meets the walls. Any thoughts on the matter would be greatly appreciated. Thanks again.

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