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Community and Q&A

Basement walls, XPS plus rockwool

wormwood1978 | Posted in Green Building Techniques on

I live in Zone 5 on the Maine coast.  The top 2 feet of my basement is above grade.  Are there any issues with placing R15 Rockwool over 2″ of XPS?

I currently have 2″ XPS affixed to my basement walls, seams all taped.  I built a 2×4 stud wall against the XPS.  I plan to fill the stud cavity with R15 mineral wool, either the Rockwool product or the Owens Corning product.  Are there any problems with this?  No leaks in the basement, I run a dehumidifier in the summer and I will have heat in the basement (although it may be infrequently ran).

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  1. ThirtyWest | | #1

    I'll leave the technical stuff to someone else. But if you haven't priced it yet, Hammond Lumuber had the best price on Rockwool a few months ago. WAY better than HD or Lowes and they delivered it for free. sorry if you already knew that.

  2. Expert Member
    RICHARD EVANS | | #2


    Your foam to cavity insulation ratio exceeds minimum dew-point requirements for your climate. You didn't mention that you plan on using polyethylene over the studs. The rigid foam seams are taped. You are using mineral wool over fiberglass.

    Increased humidity and thermal mass in a basement may complicate the usual enclosure risk factors normally seen above ground, but I still can't think of a reason why this wall would fail. You've eliminated the risk factors.

    1. wormwood1978 | | #3

      I did not plan on using poly over the studs

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