Crawlspace Insulation?
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  1. #1
    Join Date
    Dec 2003
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    287
    Hey guys, not sure if this belongs in here or on this forum at all. But since you're in and out of many crawlspaces I figured I'd give it a shot. The portion of my split level house over the crawlspace has floors that get cold as hell in the winter. Ive read 2 schools of thought on crawlspace insulation and wanted to hear your takes.

    1. Treat the crawl like a small basement and insulate the walls with r13 batts hanging from the sill plate with a 8 mil vapor barrier on the floor. This to me looks like asking for trouble with moisture if the vapor barrier isnt perfect and possible attraction of termites. I would think that the rigid foam board would be slightly more suitable but don't know.

    2. insulate between the floor joists with the paper side up and those spring loaded insulation rods. This would keep the floor warmer I think but would use a ton more insulation. You still have the critter issue to deal with. And your Vapor barrier to the living space is broken every 16 inches by the floor joist.

    There doesnt seem to be any consensus on how to go about it and I was wondering what you guys see out there that is the best. Or what the latest school of thought was in new construction.



    I should mention that I am in NJ near Philly, hot humid summers, cold but not Buffalo like - winters. Probably averages 28 or so.

  2. #2
    Join Date
    Feb 2003
    Location
    Huntsville,AL
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    4,125
    use tongue & groove Styrofoam, 2" thick -- cover with sheetrock -- both can be glued. leave 4" of masonry at bottom so can inspect for termites, etc. cover dirt with pvc or white pool linner -- hvy duty

  3. #3
    Join Date
    Aug 2003
    Posts
    626
    If you have no insulation now, the best method would be to put 3 inch Dow Styrofoam board on walls and air seal crawl from outside. You don't need to use sheet rock if you use the Dow product--it is fire rated. A 6 to 8 mil poly that covers all the ground will do fine. This should give you warmer floors and save a lot of energy. It will also prevent warm moist air coming into the dew point crawl and causing mold problems.

  4. #4
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    better read the warning on the Styrofoam boards! or visit STYROFOAM.com -- same for all insulations having combustible components, including faced fiberglass!

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,884
    Spray on polyurethane (spelling?) foam. Only has to be 1-2" thick, nothing gets by that stuff.

  6. #6
    Join Date
    Aug 2003
    Posts
    626
    What the code is looking for is a fire rating and toxic level--Dow meets the requirements and is approved. Even sheet rock only has a 15 minute fire rating, so why spend the money?

  7. #7
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,255
    I vote for foil faced foam on the walls and rim joist cavities . Heavy plastic/gravel to lay flat or concrete on the earth. Closed vents. Create gravel paths on the plastic for routine maintaince access. Monitor the %RH in the crawlspace with Radio Shack remote %RH Meter/high humidity alarm, $52. This will spot water/air intrusions and plumbing leaks. Dehumidify if necessary to keep <55%RH. This stops condensation on ducts/pipes/plastic cover/cool living area floor.

  8. #8
    Join Date
    Aug 2003
    Posts
    626
    You do NOT want foil on the insulation! That is a vapor barrier (ie. less than 1 perm rating) and will cause mold and rot on band joists!

  9. #9
    Join Date
    Jan 2004
    Posts
    108
    My own crawlspace has four inches Styrofoam on the outside all the way down to the footings. Works like a charm - the crawlspace was 68 degrees all winter, even when it gets down to 20 below outside. Six mil poly on the ground. Absolute (not relative) humidity in the crawlspace is same as upstairs or very slightly higher. I live in Northern Wisconsin, so no termites.

    If you put insulation on the inside, the walls get cold and want to condense behind the insulation in the winter. Styrofoam might work if you seal around all the edges.

  10. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,255
    Originally posted by teddy bear
    I vote for foil faced foam on the walls and rim joist cavities . Heavy plastic/gravel to lay flat or concrete on the earth. Closed vents. Create gravel paths on the plastic for routine maintaince access. Monitor the %RH in the crawlspace with Radio Shack remote %RH Meter/high humidity alarm, $52. This will spot water/air intrusions and plumbing leaks. Dehumidify if necessary to keep <55%RH. This stops condensation on ducts/pipes/plastic cover/cool living area floor.
    You need foil for fire protection to comply with the local codes. Foam also has a low perm.

  11. #11
    Join Date
    Aug 2003
    Posts
    626
    Bocca and IRC both approve Dow styrofoam in crawl applications. Dow styrofoam is NOT vapor impermeable like foil faced foam is. The wood must be allowed to dry to the inside of the crawl--foil will not let this happen, Dow product or any other styrofoam with a fire rating will!

  12. #12
    Join Date
    Dec 2003
    Posts
    287
    Bumping this back up, because I havent gotten around to this project yet!

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