peterswet
New Member
Posts:59
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| 13 Mar 2011 12:59 PM |
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Installed truefoam 2 1/2 in basement , Its a type 2 foam, heard differing opinions of where the vapour barrier should go , above or under , asked local building inspector what he wanted to see and he advised over , same as SM ,
Any opinions?
Peter |
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marrs516
New Member
Posts:8
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| 26 Mar 2011 10:51 PM |
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vapor barrier has to go under insulation, or your insulation will lose its r value |
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Alton
Veteran Member
Posts:2164
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| 27 Mar 2011 09:05 AM |
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Peterswet,
Just curious, but what did the building inspector advise? Although you used Type II EPS was it 1.5 pound per cubic foot?
Since I live and practice in the Southeast, I have not used foam under a basement slab - only under a raised slab where I place the vapor barrier under the foam. With the slab about two to three concrete blocks above the finished grade and with 6" of gravel under the slab, I do not worry much about water getting to the EPS or XPS. However, I do worry about the light-weight vapor barrier trapping air and rising up when it is placed directly under the slab. I have seen more than one crew punch holes in the vapor barrier to let out the air so the air bubble would not displace concrete which would make the slab thinner.
I do understand that installing foam under a basement slab could encounter some water. If that is the case, then I wonder if the foam board should be encapsulated with a vapor barrier on each side of the foam or would that be negated by the possibility of trapping and holding water to the foam? |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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jonr
Senior Member
Posts:5341
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| 27 Mar 2011 10:47 AM |
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My understanding is that one can use either XPS or higher density EPS and that water isn't a concern with either one.
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Alton
Veteran Member
Posts:2164
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| 27 Mar 2011 11:28 AM |
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Jonr,
Just sharing: I just learned recently that 2.8 pound per cubic foot closed cell spray polyurethane foam is also suitable for using below grade or under a slab although it will cost more. However, it is a quick way to avoid seams and to get a higher R-value in a smaller space. Now I wonder if Thermax (Aluminum skin polyisocyanurate, 25 PSI, R-value 6.5/inch) could also be used below grade. I have always limited my use of Thermax to above grade. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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radiantbarrier
New Member
Posts:74
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| 27 Mar 2011 11:45 AM |
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If you are doing radiant, look at NEW 3 inch Crete-Heat at TheGreenBuildiingProductsStore. IF you are not doing radiant consider 1 1/4 inch THE BARRIER. Has patented self sealing tape seams to ensure moisture protection and will give you a good R value in addition. |
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Alton
Veteran Member
Posts:2164
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| 27 Mar 2011 12:37 PM |
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The Crete-Heat looks interesting. However, I could not find THE BARRIER on the net. Do you have a link or more descriptive name for it? |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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JohnyH
Basic Member
Posts:114
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Alton
Veteran Member
Posts:2164
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| 27 Mar 2011 03:12 PM |
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John,
Your link worked. I did not have to coppy it. Thanks for the link. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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peterswet
New Member
Posts:59
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| 27 Mar 2011 05:11 PM |
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Alton:
It is 1.35 lbs/ft3
The building inspector required it above the insulation and tuc tape sealed to the icf as code around here apparently requires it to mitigate radon gas entry,
Ive got a good gravel bed and a low water table so Im not too worried about moisture wicking into the eps but I guess that is the worry and some folks advocate the vapour barrier being beneath the insulation
Peter |
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radiantbarrier
New Member
Posts:74
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| 27 Mar 2011 06:25 PM |
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The Barrier info is at www.TheGreenBuildingProductsStore.com We also have the tape for it that allows it to be taped to the ICF and as it is 6 or 10 mil it serves as a radon resistor.
Callie Barrett |
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eric monkman
Basic Member
Posts:262
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| 27 Mar 2011 06:44 PM |
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If vapour barrier is mandated to be to the "warm side" of a vertical wall assembly, why should it be any different if underfoot ?
Secondly, if rigiid foamboard is glued or seamed with tape, why is a poly vb necesary?
Correct me if I'm wrong ( I'm sure somebody will :-) but considering the high perms rating most Type 11 products have, why is poly even necessary ?
Keep in mind that aluminum dissolves when in contact with concrete, so foil faced products loose their rated R value. |
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peterswet
New Member
Posts:59
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| 27 Mar 2011 10:04 PM |
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Eric: Beats me why it would be different but I was informed / misinformed by the vendor Seemed to make more sense on top imho, less perforation from gravel of said VB Strangley enough if you were to purchase the truefoam sheets prefabbed for infloor heat the boards are routed out to accept the hot water pex , the VB would then be required to go beneath the rigid board. Peter  |
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