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  1. #1
    Join Date
    Jul 2008
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    46

    Default insulating crawl space

    Question regarding insulating crawl space floor. Is it wise to add insulation directly on the crawl space floor since the ground is a constant 55 F and would radiate heat keeping the crawl space area somewhat warm during the winter months.

  2. #2
    Join Date
    Sep 2012
    Location
    Boston
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    820

    Default Re: insulating crawl space

    insulating between the floor joists should be enough, do not insulate the cement floor unless you want to use rigid foam insulation. absolutely do not put fiberglass insulation on the crawl space floor.

  3. #3
    Join Date
    Jul 2008
    Posts
    46

    Default Re: insulating crawl space

    MLB why---"absolutely do not put fiberglass insulation on the crawl space floor."

    also why would you put rigid foam insulation on the floor since the temperature of ground is radiating heat at a constant 55f...

  4. #4
    Join Date
    Sep 2012
    Location
    Boston
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    820

    Default Re: insulating crawl space

    the reason you don't use fiberglass insulation on a cement floor is that it will get wet and make a nice home for rodents.

    the reason "to" insulate a concrete floor with rigid insulation is if the crawl space is accessible from a basement it will keep some of that 55 degree cold away from the basement.

    the reason "not to" insulate a concrete floor with rigid insulation is if the crawl space is accessible only from outside and in no way connected to any heated space, therefore utilizing the heat from the ground to keep the space above freezing in the winter.

  5. #5
    Join Date
    Nov 2012
    Posts
    7

    Default Re: insulating crawl space

    I may have made a mistake in how I insulated my crawl space this Fall, but I'm stuck with it and Winter is coming on. I wonder what I might do now to improve matters.

    My 1000+ square ft. house is supported by sauna tubes on a grade, the floor joists are 2 1/2 to 4 ft. above bare ground with sandy gravel added. The ground is moist though not very wet, and a lot of stuff is stored there covering much of the ground. There are no openings or vents into the house from the crawl space, and no pipes in the floor. The perimeter is roughly sheathed with plywood and there are gaps open to the outside.

    Right or wrong, I have already insulated the floor with craft backed 9 1/2 in. fiberglass batts, installed in 4 ft. lengths, paper side down. I'd like to seal the perimeter from the outside, as New England winters are very cold, but wonder whether this would trap too much moisture and the fiberglass would become moist. Would it be a good idea to install plastic sheeting under the insulation if I make sure it is tight?

  6. #6
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    1,160

    Default Re: insulating crawl space

    Quote Originally Posted by Ed2 View Post
    I may have made a mistake in how I insulated my crawl space this Fall, but I'm stuck with it and Winter is coming on. I wonder what I might do now to improve matters.

    My 1000+ square ft. house is supported by sauna tubes on a grade, the floor joists are 2 1/2 to 4 ft. above bare ground with sandy gravel added. The ground is moist though not very wet, and a lot of stuff is stored there covering much of the ground. There are no openings or vents into the house from the crawl space, and no pipes in the floor. The perimeter is roughly sheathed with plywood and there are gaps open to the outside.

    Right or wrong, I have already insulated the floor with craft backed 9 1/2 in. fiberglass batts, installed in 4 ft. lengths, paper side down. I'd like to seal the perimeter from the outside, as New England winters are very cold, but wonder whether this would trap too much moisture and the fiberglass would become moist. Would it be a good idea to install plastic sheeting under the insulation if I make sure it is tight?
    Yes you wrongly insulated the crawl space. The insul should go between the floor joists and plastic over the earth. You didn't mention insulating the walls of the crawl space. Yes moisture will be trapped. The crawlspace should be ventilated unless it becomes part of the conditioned space, which in your case I don't see how it could.
    ps. sona tubes(a brand name), not sauna tube.

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