I posted earlier in construction techniques. I live in New England. I am converting an attic over the family room to a cathedral ceiling in the family room. The roof rafters/ceiling joists are 2×6, 12′ span and 16” oc.with 1×3 strapping. There are no ridge or soffit vents. I am using R19 fibreglass insulation. Does it make sense to use those styrofoam or plastic sheathing vents against the roof sheathing, since they would vent to no where.
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Hi Kevin- The styrofoam vent would not serve any purpose in your setting. They are designed to allow for unobstructed air flow from the soffit to the ridge which you don't have because your building a "hot roof", one without venting. There is a discussion on these in previous FHB but the short of it is that they work but you need to pay attention to details. i.e. you can't have warm heated air from the house passing up thru the insulation as it will eventually come in contact with the cold outside air and then you have condensation. Your cathedral ceiling rains !! To aviod this you need two provisions. 1.Sufficent insulation to prevent reaching the dew point within the insulation and 2.An intact perfect vapor barrier to prevent the hot air from penetrating the insulation like a 6 mill visquine barrier. Hope this helps, John