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Block Basement Walls.

Post in 'DIY and General non-hearth advice' started by JA600L, Apr 15, 2014.

  1. JA600L

    JA600L Feeling the Heat

    Joined:
    Nov 30, 2013
    Messages:
    318
    Loc:
    Lancaster Pennsylvania
    Hi guys,
    I have block basement walls with dry lock on them. I am interested in insulating this further as this is the woodstove room. I started out by pulling the loose fiberglass bats out of the header and air sealing that with caulk. Is it worth while to install something better here or hang the old Bats back up?
    I have never had water in this basement and no sump pump. If I hang foam do I need an air gap between the block and foam? What thickness of foam do you recommend? I will be installing a hearth when done.
    Any other ideas for me? Thanks,
    Jeff

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  2. midwestcoast

    midwestcoast Minister of Fire

    Joined:
    Oct 9, 2009
    Messages:
    1,615
    Loc:
    NW Indiana
    I'd be tempted to put some more insulation in the header (rim joist) bay, but you could get by with what you have. Do you think you got it air sealed well with the caulk? I ask because parts of mine would have been nearly impossible with just caulk... I cut pieces of foam board to fit each bay & used Great Suff to seal around the edges & hold it in place, then fiberglass over that (non-living space). You could re-use the fibeglass that way.

    You don't need an air gap btwn the block & foam and it's better if you don't have one. You should be able to stick the foam directly to the block with using Foam Board adhesive. With the adhesive use a pattern that will restrict air movement both vertically and horizontally in the tiny gaps btwn the foam and block. Tape all seams on the foam board and seal it top & bottom.
    In your area I THINK you could get away with an inch of XPS foam if you are planning to build a stud wall inside of the foam, but you should really get a better source for that info. I'm just guessing. If the foam is too thin you can have condensation problems... Use any scrap leftovers in the rim joist bays.

    You need to cover the foam with a fire barrier (drywall) so you either build & insulate a stud wall inside the foam or put strapping on it & hang drywall on that.
  3. begreen

    begreen Mooderator Staff Member

    Joined:
    Nov 18, 2005
    Messages:
    45,989
    Loc:
    South Puget Sound, WA
    http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall
    http://www.thisoldhouse.com/toh/video/0,,20503345,00.html

    You'll go through a lot of adhesive and will want a commercial sized caulking gun to accommodate 28oz tubes. Consider buying a case of the adhesive to reduce costs. I didn't use the PL300 foam board adhesive because HomeDepot only had the smaller tubes. Instead I used the 28 oz. PL Premium which they had in cases of 12 tubes. This was label rated as OK for bonding foam to concrete. The foam board has been up for 8 years now in our tall insulated crawlspace.
    Last edited: Apr 18, 2014
  4. JA600L

    JA600L Feeling the Heat

    Joined:
    Nov 30, 2013
    Messages:
    318
    Loc:
    Lancaster Pennsylvania
    It was difficult to culk in there but I managed with the help of some spray foam. I decided to replace the fiberglass with roxul r15. It fit very tight in there so it should be sealed of pretty well. I figure I will just add the used fiberglass bats to the attic. I just need to figure out what r rating I need for the walls.
  5. Laurent Cyr

    Laurent Cyr Member

    Joined:
    Dec 14, 2012
    Messages:
    145
    Loc:
    Quebec, Canada
    When I finished my basement, I glued 2 inches oof pink foam to the walls and sills. The foam acts as a vapour barrier. I then build my 2x4 walls up against the foam, and added fiberglass batts. Then I added my sheetrock. I can really feel the difference in the heat in the basement. My wood stove is in the basement, and it takes no time at all to heat it. The heat rises to the main floor through some floor vents and via the stairwell. When adding the foam boards to the sill, I spray foamed around the cavity. I also tuck taped the joints of the foam on the walls. Best investment so far for me.

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