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insulating crawl space

Post in 'DIY and General non-hearth advice' started by chrisasst, Jan 23, 2013.

  1. TheMightyMoe

    TheMightyMoe Minister of Fire

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    If it's draft that is getting you, and you can fit down there, the easiest fix is to go around with caulk gun / canned spray foam and just fill up any holes/gaps on the outside wall.

    Once you have the draft fixed then you can decide if you need insulation (Which you likely do, but air sealing will make a BIG difference)

    Make sure you have a vapor barrier on the floor, and it is completely sealed.

    If you decide to insulate, you can put up fiber glass batts on the outside wall. This is assuming the crawl space is dry. This is the BANG FOR BUCK option, I did this with R38, and my crawl space has been 10-20* warmer since.

    If your gonna fork out money, I would simply follow everyone elses advice, and pay a professional to come spray foam the perimeter wall. Air tight, water proof, with a high insulation value. Nothing wrong with that.

    I'm not a fan of just insulating between joists, bu to each his own.

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  2. Trilifter7

    Trilifter7 Feeling the Heat

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    That was another thing I was thinking of. Thanks for the info. I think I'm going to look at sealing up the crawl first then insulating the floor later.
  3. Trilifter7

    Trilifter7 Feeling the Heat

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    Yea I'm def thinking sealing the crawl up is the first thing to tackle
  4. peakbagger

    peakbagger Minister of Fire

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    One thing you dont want to do is seal up the crawl space tight with no ventilation. I have seen some camps that were sealed up and the floor joists were like sponges after a few years. There are contractors that come in an lay some sort of plastic down on the floor and up the walls and seal all the seams to keep moisture from the ground from getting under the house and I even think they install some vents.
  5. TheMightyMoe

    TheMightyMoe Minister of Fire

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    ""Assuming it is a dry crawlspace""

    If your walls leak waters, you got other issues...

    If you vapor barrier the floor, with proper air sealing, moisture should not be getting in the home/crawlspace.
  6. Highbeam

    Highbeam Minister of Fire

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    No, there are actual official standards for doing this with no vents. Just look at it like a basement with a low ceiling height, you don't ventilate your basement do you?
  7. Highbeam

    Highbeam Minister of Fire

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    I've never been to Alaska but here in the northwest we have something called groundwater. You dig a hole in your lawn and the next morning it will have water in it even if it is not raining. During the wet season especially, it will come in from below the home and most houses in low elevations will have water in their crawlspaces under and/or on top of the plastic vapor barrier. The walls are not leaking, this is not surface water.

    Folks do all sorts of things like sump pumps and drains to get rid of this water. Lots of sump pumpers on this board and it's not because of leaky walls.
    Trilifter7 likes this.
  8. TheMightyMoe

    TheMightyMoe Minister of Fire

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    Then it would not be a very dry crawlspace. Sounds like you live somewhere with a high water table. I live in a desert thankfully.
  9. Highbeam

    Highbeam Minister of Fire

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    I dare say that more often than not, folks have moisture issues in a crawlspace. Some of the smarter builders have begun to backfill the crawlspace excavation so that the groundwater level is not above the soil level in the crawl. Thing is, you need undisturbed soil for any concrete support pads on the crawlspace floor so you need to pour some thick pads.

    My crawl is now dry. It had 6" of water in it when I bought the house.
  10. Trilifter7

    Trilifter7 Feeling the Heat

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    What did you do to get the water out? My crawl never stays wet but I have a sump pump that only runs when it rains. If its dry outside its normally dry under my crawl. One issue I have is that the floor was insulated and it must have gotten wet bc someone ripped it all out and left it in piles down there. I believe my moisture problem is due to saturated batten rotting in my crawl. I suppose a start will be to clean it out then insulate the outside masonry walls and seal up any leaks. Would batten or foam sheets be better on the masonry walls?
  11. firefighterjake

    firefighterjake Minister of Fire

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    When we bought our home it said in the crawl space there was a "damp" area . . . in the Spring we learned that what this meant was 3-6 inches of water . . . we have since put down crushed rock and a vapor barrier . . . but we still get the water coming up through . . . sump pump takes care of most of it though.
  12. Highbeam

    Highbeam Minister of Fire

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    I live on a hill. So I dug under my footing to the lowest point in my crawlspace, then installed a pipe with slope that drains any water downhill to where it daylights. I also regraded around my home so that I have 15' in all directions sloping away from the house at 2%. Then I installed a curtain drain (aka french drain, burrito drain, etc.) at that 15' distance as well as a new downspout collection system that also drained well down the hill. My goal was to remove any potential surface water source and have an emergency crawlspace drain just in case.

    It's dry down there now. Only damp dirt under the new plastic.

    People have gone so far as to pump concrete into their crawlspaces to pour a "rat slab" whatever that is.
  13. begreen

    begreen Mooderator Staff Member

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    Not just in the west, my SIL has this in her house in Mass. too. It has to do more with local topography. If there is clay underneath the top soil, moisture is going to rest there. A lot of the area north of Boston is built on swampland that stay at near saturation year round.
  14. begreen

    begreen Mooderator Staff Member

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    Highbeam is correct. You need to evaluate the soil and house before deciding to do this. Our house has wide overhangs, good gutter drain system and soil that drains straight down. That makes for a nice dry crawlspace. After 6 years we have had zero issues with our sealed crawlspace and a lot of benefit.

    Ironically an open crawlspace can be the source of too high moisture too, especially back east with their humid summers. If the crawlspace is much cooler than the humid outside air (and it often is) moisture can condense on the joists and sills.
  15. Trilifter7

    Trilifter7 Feeling the Heat

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    Good to know. I'm not thinking of sealing it off completely right now. I think I will work on insulating the masonry walls and getting the vents so I can seal them off in the winter and open them up in the summer

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