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Steve Andrews
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Posts:334
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| 11/08/2000 5:17 PM |
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[Lowell Prag posted this question on a building science website, but is glad to have it posted here as well.]
Does anyone actually have data on any problems associated with using roof SIPs (superinsulated panels) under a single membrane epdm roof?
Theoretically, since the vapor barrier (the epdm) is not to the warm side, the dew point may fall within the SIP and cause a freeze/thaw cycle.
To avoid that, an upside down roof is usually recommended without SIPs, with the insulation ballasted on top of the epdm. That is fine for flat roofs but how does one deal with pitched roofs using epdm?
Also, is having the vapor barrier to the cold side really a problem with SIPs? I know the early homes built in Canada under the r-2000 program had many problems with the dew point falling within the wall and roof section
but they were not using SIPs.
It seems to me that if one used either extruded styrofoam or polyurethane within the SIP, pressure treated studs within the SIP, and an outdoor rated plywood over the SIPs, it would not degrade even if the dew point falls within it.
In short, if that is correct, one could reliably use SIPs for both flat and pitched roofs and then use whatever roofing material one prefers on top of them, including epdm.
Any proven answers to this?
. From: Lowell Prag - Email: aj574@detroit.freenet.org
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