Insulating half a roof, from the top. What to use?
Location is climate zone 6.
Have a home with straight gable. The client wants to replace just one side of his roof/ceiling with new insulation. Attached is a photo of what the previous contractor did on the other half of the roof. Roof/ceiling is cathedral and thus the only space available is rafter bays/ possibly adding insulation on top of rafters. The roof must be accessed from the top after removing the sheet metal. With such limited options (and only being able to improve half the roof) what would be my best option for insulation/improving this bad situation?
Fill the bays with Closed cell? Is it worth the money for half the roof? Roxul batts, an air barrier and vent on top? If I put foam on top of rafters, how can I hide a lopsided roof?
Best place to put air barrier? how can I add a vapor barrier?
Any suggestions appreciated.
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Replies
Again, as Dana just wrote, in no way can closed cell insulation be reasonably recommended on a site called Green Building Advisor. It is terrible for human health and the environment, with blowing agents causing greenhouse warming of the planet and environmental toxicity for humans and other animals.
I can't tell from your drawing what the rafter spacing is, but Roxul batts sound like a good choice. You could also consider damp sprayed cellulose or you could look into a product just uncovered on this forum: Knauf Jetspray: http://www.knaufinsulation.us/en/content/jetspray.knaufinsulation.us
I think you'll want to try to maintain the venting cavity, and I'm not sure from your description if you can change the overall profile given that you're only doing 1/2 roof. You could run a smart membrane over the cavities, dense pack cellulose, add furring strips horizontally, and then attach metal roofing as you show since the ripples in the roof allow for venting. Someone else here may disagree, but you could potentially sheath over the rafters, fill the bays, and reapply the metal roof since the ripples in the metal act as a ventilation cavity. Is the roof vented at the peak?