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Community and Q&A

Crawl space ventilation and insulation

John Oliver | Posted in General Questions on

My son has a 2 story house in West central Colorado built in 2000 that has radiant heat. A 22′ x 42′ x 40″h dry, stone floor crawl space exists beneath the house and 4 evenly spaced 8″ x 16″ screened, vent openings exist at the top of each of the 42′ walls. The sill plate constitutes the top of the openings.  The PEX radiant tubing long runs are not insulated and are stapled to the perpendicular I-joists.  The copper water pipes from the 1 1/2″ main to all that it feeds are exposed/uninsulated.  The radiant tubing that heats the first floor is stapled up and covered by R38 faced fiberglass; face is up.  I think the only reason the copper hasn’t froze is because the radiant tubing heat loss is keeping the crawl space warm enough to prevent that.
He wanted me to seal off the 8 vent openings to conserved heat.  I don’t want to do that because I ‘m confident a mold growth problem will occur.  I think the better investment is to insulate all of radiant and copper tubing.
Is the old man wiser than the son?

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  1. Jon R | | #1

    I wouldn't trust pipe insulation to prevent freezing - but I would trust antifreeze.

    There are various ways to prevent mold in a sealed off crawlspace. For example, a dehumidifier or some dry air from the interior.

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi John,

    Most of the expert I have worked with considered sealed crawl spaces the best way to go, with a few exceptions. This article will help you make your decision: Building an Unvented Crawlspace

  3. Expert Member
    Dana Dorsett | | #3

    >"...West central Colorado ..."
    >"...dry, stone floor crawl space ..."
    >"He wanted me to seal off the 8 vent openings to conserved heat. I don’t want to do that because I ‘m confident a mold growth problem will occur. "

    I'm not sure where that confidence is coming from. With a damp dirt floor crawl space in a more humid climate that confidence would be rational, but in high-dry western CO probably not, even if you DIDN'T put down a ground vapor barrier.

    But in western CO even with an absolute parched-dry stone floor you'd still want to install a vapor barrier for radon control, and install a tiny exhaust fan to depressurize the crawlspace relative to the conditioned space above.

    Also, insulating the crawlspace walls to a code-minimum R15 continuous insulation thermally couples the crawlspace to the subsoil (or in your case possibly bedrock), which goes a long way toward freeze protection for plumbing located in the crawlspace.

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