Basement insulation -- XPS on just exterior walls?

Discussion in 'Remodel Forum & Blog' started by ironspider, Jan 5, 2010.

  1. ironspider

    ironspider Member

    Messages:
    68
    Location:
    Michigan
    Greetings all! Well the time has come for us to finish our basement "main room" and I have a quick question about the insulation of the walls.

    First the layout: The room is essentially a square with 2 foundation walls (which obviously are against the earth/underground) and 2 interior walls (both made of concrete block -- separating us from other unfinished but heated basement rooms).

    So, my insulation approach for the exterior walls is going to be to attach 1.5" Extruded Polystyrene Foam panels to the walls with the proper adhesive and then frame out the walls and if the 7.5R value of the XPS doesn't make the temp come up a little [it's about 65 degrees in that room in its current unfinished state -- and it's 9 degrees outside] do some fiberglass batting in the stud cavaties.

    SO, my question is this!: This XPS isn't the cheapest stuff in the world and I am wondering if that is needed on the INterior walls? (the walls that separate this room we are finishing from the other basement rooms)? The walls of this room are like 27' long so that could save me a lot of money. And it will also save me the 1.5" of wall space tha I wouldn't have to come in without the XPS board. But of course I'm willing to buy the stuff if there's a compelling reason.

    Thanks in advance!
  2. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,236
    Location:
    Land of Cheese
    I see no valid reason to insulate an interior wall. In a basement you need airflow and humidity control. Insulating the interior walls would be more likely to cause problems than good.
  3. Bosun

    Bosun New Member

    Messages:
    89
    Location:
    Minneapolis
    I'd build the stud walls and do yout electrical--then I would spray foam.
  4. khali

    khali New Member

    Messages:
    5
    Location:
    Houston
    I have applied Polyurethane Foam closed-cell insulation materials. It’s materials offer high R values, one can use a thinner foam board to have the required thermal resistance one desires. This can be extremely helpful if there are space limitations involved. This strength involved the ability of the foam to resist deformation and the ability to main its shape when forced or loaded down.It can handles a wide temperature range, which makes it effective as a roof insulation. When combined with laminated aluminum foil facing, it is also an effective moisture and vapor barrier.
    Last edited: Apr 28, 2010
  5. bmb2m9

    bmb2m9 New Member

    Messages:
    22
    Location:
    Jefferson City, MO
    I would use polystyrene on the exterior walls with an r-13 to r-15 fiberglass insulation and then add a vapor barrier. You can just use the fiberglass on the interior walls with no vapor barrier or polystyrene. This would be the best r-value for your money.

    That being said, spray foam will give you the best final product, however it is usually not a DIY product and much more costly.
  6. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,236
    Location:
    Land of Cheese
    Below grade walls can only dry to the inside of a structure. Using a vapor barrier as you suggest will trap moisture in the fiberglass insulation.
  7. bmb2m9

    bmb2m9 New Member

    Messages:
    22
    Location:
    Jefferson City, MO
    If you have moisture problems, you probably should not consider finishing your basement.
  8. Alton.cedric

    Alton.cedric Guest

    I would paint the exterior walls with a bast. waterproof paint, R-11 to R-15 with a vapor barrier is plenty of insulation. I would insulate the rim joists with R-19 and only about 2' in from the wall. I do not recommend the whole ceiling.
Similar Threads: Basement insulation
Forum Title Date
Remodel Forum & Blog Basement insulation question Mar 12, 2014
Remodel Forum & Blog Basement insulation Jan 21, 2014
Remodel Forum & Blog Uneven walkout basement external wall's insulation Feb 2, 2013
Remodel Forum & Blog Basement Wall Insulation and Buildout Jan 1, 2013
Remodel Forum & Blog basement wall insulation Sep 25, 2012

Share This Page