Cathedral ceiling insulation
I am looking at insulating a house that has a simple gable end roof with a 10/12 pitch. It has 24″ deep open web trusses 24″ OC . It is going to have a metal roof but currently just has the underlayment.
The general contractor had originally thought 2-3″ of closed cell directly to the bottom of the roof deck then extra fiberglass batts. For the same money I could deliver about twice the R- value with open cell but should also spray the foam [skin still on since no trimming necessary] with a vapor retarder paint.
Looks like it could be vented with continuous soffit to ridge vents which obviously is the best way but the peak is over 35′ above the floor and the contractor did really want to go there. The ceiling is going to be tongue and groove wood perforated with openings for can lights speakers, etc. so not really any air barrier.
The orientation is such that both sides of the roof will see good sunlight during the winter. At just under 5000 sq.ft. of roof with most all of it way up there staging and safety is an issue.
I would prefer to install vapor permeable vent chutes then a minimum of R-40 open cell. I have used open cell foam for similar applications for over 20 years with out a recall being careful about the north sides of steeper roofs. I have also used a lot of closed cell but the only concern is the potential for a roof leak going undetected and the cost.
I know there are differences between the brands of open cell foam in terms of water absorption,etc. My feeling is that it would be fine without venting and the vapor retarding paint on the foam skin but would prefer to have a vented roof. The extra time and hassle it would take is nothing to what it would take if we have problems down the road due to high humidity or whatever. If I can not talk him into a vented assembly what is the better approach?
Not cost effective for total r value with closed cell alone. Also don’t really want to go over the whole area a bunch of times. Climate zone 5b mixed hot and humid summers, can be pretty damn cold and windy in the winter.
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