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Old 01-30-2020, 08:41 AM   #1
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Crawl Space Insulation Question


I am looking to insulate and vapor barrier my crawl space... I have seen several ways of doing it but would like to know which is the RIGHT way. I don't want to have mold issues or ineffective insulation.

I have as the outside board 3/4 green treated plywood do I attach the vapor barrier mil to that then put the poly foam board on .... or the poly foam board on first to the plywood and then the vapor barrier?

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Old 01-30-2020, 08:44 AM   #2
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Re: Crawl Space Insulation Question


Are you talking about the rim or do you have stem walls?
Are thinking encapsulating?
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Old 01-30-2020, 08:58 AM   #3
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Re: Crawl Space Insulation Question


The foundation studs are 10x10 green treated then the 3/4 inch green treated plywood on the outside of that all the way around the cabin, sand floor. Yes total encapsulate with spray foam on the floor joists all the way around the outside as well.
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Old 01-30-2020, 09:04 AM   #4
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Re: Crawl Space Insulation Question


I just want to know the correct way to put on the vapor barrier... I have seen pictures of several different ways. Do I put the barrier over the poly sheets attached to the plywood or under it... then where do I stop at the top? Right at the floor joist or take it up a bit and spray foam over it?
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Old 01-30-2020, 09:21 AM   #5
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Re: Crawl Space Insulation Question


insulation under plywood sounds like you are talking about the floor, that is not what is usually referred to as encapsulating
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Old 01-30-2020, 09:31 AM   #6
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Re: Crawl Space Insulation Question


No the cabin is on 10x10 pillars some in the middle for support most on the outside edge of the crawl space ... the entire outside then is covered in 3/4 green treated plywood, from the floor to the ground. no insulation on the 3/4 plywood on the inside of the crawl space... when I add the vapor barrier and insulation on the inside of the crawl space what goes first the insulation on the green treated plywood or the poly? Its that simple - I have seen pictures of companies doing to both ways which is correct in my situation? Then how far up do I take it to the floor joists when I spray foam - do I stop at the top of the poly insulation or do I take it up a bit over it and then spray foam the floor joists all the way around.
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Old 01-30-2020, 09:33 AM   #7
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Re: Crawl Space Insulation Question


This way or the vapor barrier on the outside?
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Old 01-30-2020, 09:37 AM   #8
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Re: Crawl Space Insulation Question


OR this way... ?
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Old 01-30-2020, 09:40 AM   #9
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Re: Crawl Space Insulation Question


Only difference is I am using poly foam board 2in. insulation instead of spray foaming the hole thing ... just spray foaming the floor joists at the sill plate. second pic is not professional but I have seen it done that way as well on pro websites...
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Old 01-30-2020, 09:43 AM   #10
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Re: Crawl Space Insulation Question


Quote:
Originally Posted by olbaidhh View Post
This way or the vapor barrier on the outside?
I would do it just like the picture with the poly up the walls some the foam doesn't need another poly. If you put it all the way up I would stop it at the top of the concrete.
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Old 01-30-2020, 06:35 PM   #11
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Re: Crawl Space Insulation Question


Common practice is to install the vapor barrier on the warm side.
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Old 01-30-2020, 08:22 PM   #12
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Re: Crawl Space Insulation Question


I think the jury is still out on encapsulation. I fixed my summer moisture problem by closing nearly all my vents and running a dehumidifier. I have always seen the barrier go on the foundation wall then the foam.
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Old 01-30-2020, 08:25 PM   #13
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Re: Crawl Space Insulation Question


The quote I got on my encapsulation was nearly $7K. That would replace lots of joists IF they would ever have problems. I do not know why floors are not made of dried treated lumber and marine rated plywood. Seems like it would save so much trouble in humid climates...
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Old 01-30-2020, 08:26 PM   #14
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Re: Crawl Space Insulation Question


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I think the jury is still out on encapsulation. I fixed my summer moisture problem by closing nearly all my vents and running a dehumidifier. I have always seen the barrier go on the foundation wall then the foam.
That argument is about wood structure most people use foam board for both. And just seal the poly to that.
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