Closed-cell, spray polyurethane foam (SPF) may be used to construct unvented cathedral roofs and cathedralized attics. It can be applied in sufficient thickness to satisfy local energy code requirements, directly to the underside of roof sheathing between rafters or joists of any slope in all (heating, mixed and cooling) climates.
This configuration controls the entry of moisture-laden air into the insulation and also eliminates dew-point occurring at the underside of the roof deck and anywhere in the insulation, in all (heating, mixed or cooling) climates*. Due to the fully adhered, closed cell properties of SPF, air and moisture are displaced out of the insulated space including at rafters and sheathing. Moisture cannot enter the insulated space from any direction, eliminating the requirement for roof venting.
Venting above the closed cell SPF could reintroduce moisture laden air into a new air space below the roof sheathing, which may introduce
another moisture condensation problem. Therefore, venting above the SPF in these configurations is not recommended.
*(Assumes the suitable thickness of SPF is applied to prevent condensation)
Cathedral Roofs/Vaulted Ceilings
Cathedral Roofs/Vaulted Ceilings Before
Cathedral Roofs/Vaulted Ceilings After
Completed by Houle Insulation
Credit: sprayfoam.org - Click here for more details.
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