unvented roof, spray foam, indoor pool
capo
| Posted in Energy, Heating & Insulation on
I am building an addition in San Carlos, CA (SF Bay peninsula). The room is about 19′ x19′, 8′ tall ceiling, and has an 8′ x13′ endless pool. (The pool will be covered when not in use.) The roof/ceiling is unvented, low-slope with liquid roofing (Pacific Polymers). The trusses are about 12″ to 13″ tall at the walls and roughly 14″ to 16″ at the ridge. I would like to use open-cell icynene spayed thick enough to get R-30. (If the roof leaks, I would like it to drip through the insulation). In an unvented roof, does the spray foam need to fill the cavity completely. If not, what are my vapor barrier options/requirements. The ceiling will be painted drywall.
Replies
Sprayfoam insulation is done here regularly, a lot of it to the underside of a roof deck framed with 2x12s at 24 centers. We are in a zone 3 climate and need something like R49 or better in ceilings under roofs. Cavities never get packed out.
Can you get a quote from someone doing closed cell foam? It is more impervious to moisture penetration than what you propose.
What I have seen done in a room like what you have, is foamspray in the framing cavities (never filling them completely), and then the bottom side of the rafters sheeted in 1" foam Thermax board, the joints all taped. Ceiling finish goes over the Thermax, using long enough fasteners to fix into the rafters, above.
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See also the replies to the identical post over on JLCOnline. Concern is that the roof design may result in water unable to dry to either side and become a rotted mess in short time. Advice there was to use vapor barrier, well detailed, and good HVAC to control the humidity.