Vented or Unvented Soffit for Flat Roof
I have a mid-century home with a flat rubber roof. The pitch is 0.6:12 and there is no attic. The cavity is only the size of the ceiling joists (7.5″) which also serve as the roof joists. Aluminum backed drywall was used with fiberglass in the cavities. We are re-siding the house and trying to decide between unvented and vented soffit. The original construction was unvented plywood soffit, but it appears that vent holes were added when the house was last sided.
Given some previous answers it appears that the original construction goal was to have a sealed system with dual vapor barriers (aluminum and roof membrane) above and below the roof structure. If that is the case, then this intended structure may have been compromised by adding the vents.
Should we continue with vented soffit or return to the original unvented configuration?
Thanks in advance.
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Replies
TCastle,
This is a tricky one. You have an assembly which often experiences problems, that hopefully has reached some sort of equilibrium and is doing okay. The question is whether that is due to a small amount of drying the soffits may allow, or that the assembly is sufficiently air-tight that it excludes moisture from getting into it. My guess would be the latter, and I would use un-vented material for the new soffits.
Assuming you're referring to air moving from the living space, I think it is doing well because there are very few openings in the ceiling. Only three surface mount light fixtures. About a year ago I had to move one. Around the same time I had to repair the ceiling following a leak near the chimney. In both cases I saw no glaring evidence of moisture intrusion.
Would you recommend covering the holes drilled in the plywood soffit, or will adding non-vented PVC soffit essentially take care of that?
TCastle,
I think adding the new soffit will be sufficient.