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fish
Joined: 27 Jul 2005
Posts: 15
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 Posted: Sat Dec 15, 2007 5:07 pm Post subject: Flat roofs insulated w/ EPS - vapor barrier required? |
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On my new home, I want to frame the roof totally flat with small timbers and use 1x or 2x tongue & groove decking over. The timbers and decking will be exposed on the inside. On top of the timbers, I want to lay tapered EPS w/ a 1/4 - 1/2" pitch followed by EPDM and small river rock (1.5" dia) for ballast.
How should i deal with vapor diffusion? I'm concerned that if I install a vapor barrier on top of the decking (under the EPS), moisture will accumulate on top of the wood decking and eventually wreck havoc.
There seems to be much controversy between the "experts" on the use of vapor barriers, roof ventilation and the like...and that's on conventional roofs with much steeper pitches. Solid information on the above "flat roof" scenario seems virtually nonexistent.
Can anyone here advise?
I will be building in a temperate locale which will require heating 4 months of the year. The R-value of the roof will average around 40. Internal moisture will be minimized via mechanical ventilation above the cooktop, shower & laundry.
Thanks. |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Sat Dec 15, 2007 8:59 pm Post subject: |
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fish,
I would talk to the EPS manufacturers rep about your particular project. The makers claim the insulation has a relatively low perm rating and does not promote any kind of moisture accumulation in the material. The fact that you are not building near the artic circle should lessen your concern about installing a vapor barrier. Also as you are aware, controlling interior humidity levels is critical in any colder climates.
You may also want to browse the BSC web site (Building Science Consulting) to see what they may have to say about the subject.
Good luck with your project. |
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fish
Joined: 27 Jul 2005
Posts: 15
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| Posted: Sun Dec 16, 2007 10:44 am Post subject: |
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Thanks, Birgco.
I poked around on the BSC site and found some excellent info. Very helpful. Thanks again! |
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