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Thread: slab under box out

  1. #1
    DIY Senior Member Master Brian's Avatar
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    Default slab under box out

    I have two boxouts on my 1915 bungalow, both are block walls to the ground with minimal footings. Not sure if the boxouts are original, but they've been there a long, long time. House is a 1915 Craftsman Bungalow.

    Currently these crawlspace floors are dirt, but I'm wanting to pour concrete slabs. Both of these crawlspaces are accessible only from inside the house and I don't like the idea of dirt on the inside. Too easy for bugs and other critters to get in. The other reason is so that I can insulate the area(s) better. I figure if I have a concrete floor, I can then build 2x4 walls and insulate those walls. Currently the walls are just 3/4" rigid foam panels over the block. At least it's something, but not great.

    Question is, how thick would you pour the floors? Should I put any steel mesh down? What about foam under the concrete, I've heard of that to aid in R value.

    My neighbor is a mason, so I'll be using his mixer, but using quickrete premix, most likely.

    Other than building a few small walls to hang insulation in, the only other thing I might do is store plastic tubs in these areas for things like christmas decorations and such, so no real weight and non structural.

    Thanks...

  2. #2
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    I would put down at least 3" thickness and maybe thicken it around the edges if you're intent on concrete. No mesh--it's taking no weight.

    Better yet, just grade the area flat and put down a few layers of preformed foam insulation cut to fit tightly. You can do it on the floor and on the walls.
    Lay a sheet of 1/2 OSB or ply on that and you'll be good to go for storage.

    Jason

  3. #3
    DIY Senior Member Master Brian's Avatar
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    Quote Originally Posted by Lakee911 View Post
    I would put down at least 3" thickness and maybe thicken it around the edges if you're intent on concrete. No mesh--it's taking no weight.

    Better yet, just grade the area flat and put down a few layers of preformed foam insulation cut to fit tightly. You can do it on the floor and on the walls.
    Lay a sheet of 1/2 OSB or ply on that and you'll be good to go for storage.

    Jason

    I wouldn't say I'm intent on concrete, just don't know what else would provide as good of a barrier against moisture intrusion and insect/rodent invasion.

    I like the idea of foam and OSB, but they say 5-6" between soil and wood to protect against termite damage. That's a lot of rigid foam. I did think about laying some extra concrete blocks down and laying 1/2" cement board over that, but not sure if that would provide the barrier I'd like.

    For what it's worth, this house has had previous termite damage, it has been treated and I can't find any new/current signs of invasion. The problem area was close to both of these boxouts. So, I don't want to take any chances...

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