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  1. #1
    Join Date
    Apr 2013
    Location
    Massachusetts
    Posts
    28

    Default R value for walk out basement

    On the 2009 IECC page for MA LINK, I see Basement Wall R-value c 10/13.

    Are those the values for a walk out basement too, where the back and part of the side walls are exposed?

    Want to make sure I understand this, the continuous sheathing R value of 10, that's when you have no gaps in the insulation, like what you'd have with studs against the wall, right? So, if I use the technique in this vid LINK, I'll only need R10? Is the idea that if you don't have thermal bridging, you don't need as high an R value?

    If you were insulating a basement in my climate zone, do you think R10 is good? Or would you go for an R21 solution like the one shown in this vid LINK? Or, would that be overkill?

  2. #2
    Join Date
    Mar 2009
    Posts
    1,387

    Default Re: R value for walk out basement

    Howdy i would go r-25 but i try to reduce my heating load in my basement. Moving the studs away from the foundation walls a couple inches reduce the heat sink issues. Insulation spray applied foam or rigid foam between foundation an studs is a good starter. So are you going to insulate the slab too -money well spent...
    Any an all of my comments are just my opinion and not to be confused with facts.

  3. #3
    Join Date
    Apr 2013
    Location
    Massachusetts
    Posts
    28

    Default Re: R value for walk out basement

    Quote Originally Posted by Timothy Miller View Post
    Howdy i would go r-25 but i try to reduce my heating load in my basement. Moving the studs away from the foundation walls a couple inches reduce the heat sink issues. Insulation spray applied foam or rigid foam between foundation an studs is a good starter. So are you going to insulate the slab too -money well spent...
    Thought I was subscribed to this thread, doh! Anyway, R25 is a high number. I could get that with 2" XPS foam boards glued to foundation walls, then use roxul batting in stud cavity for R15. I'm leaning towards 1" XPS though cause I'm not sure if the the extra R5 is worth it?

    For the slab, I'm considering an underlayment called DMX 1-Step, LINK. It's a vapor barrier and insulation combo, has an R value of 2.2. Then a floating engineered floor right on top.

  4. #4
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,381

    Default Re: R value for walk out basement

    If you are putting insulation in the stud bays, it is not continuous insulation. Continuous insulation would be like panels glued to the basement walls.

    For the walls that are covered by dirt on the outside, R-10 continuous is plenty. Those walls will have a pretty stable temperature. The walls, or parts of walls that are exposed to the weather on the exterior side could use a little more insulation, like the R-20+. Those walls will be much colder in winter and hotter in summer.

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