My roof strategy
This site is wonderful. I’ve gotten loads of useful advice by asking questions, reading articles, and following discussion threads.
I am about to have a conversation with my builder and framer about the roof assembly for my new house. It will be a thick roof (see Roof detail copy.jpg) with a combination of exterior and interior insulation. Since the builder and framer have not done this type of assembly before, I want to gather a little more information before making this key decision.
The second story is a simple gable roof. The story has three sections (a central area with the stairwell, bath, and laundry and rooms at either end of the floor) The end rooms are vaulted to the ceiling, but we are dropping the ceiling in the middle section to nine feet.
I plan to install 6 inches of iso outside with about 8 inches of rockwool between the rafters. (I’m afraid that more than 6 inches of insulation on the outside will make our small cottage look “top heavy.”)
This much insulation is probably overkill for Zone 3, but I am inclined to do. The roof assembly will be unvented.
So what would be the easiest way to air seal the assembly? The vaulted areas seem straightforward, but I’m not sure about the area were the ceiling drops. Does it matter that the dropped ceiling will create an unvented attic space in the middle of the floor? If everything is drywalled, caulked, and taped, will we be okay as long as there are no opening between the unconditioned and conditioned spaces.
And how should the roof assembly be done exactly? I don’t want exposed joists or cables. Could we use a post and ridge beam strategy instead (something like the illustration in Ridge beam assembly copy.jpg). To be on the safe side, should be put in joists in the dropped middle section of the floor to make everything stronger?
Instead of solid rafters, would there be any advantage or disadvantage to using chord trusses (similar to Chord Truss for Cathedral Ceiling.jpg).
FTIW, I don’t think the framer will have any problem building the roof assembly. I’m sure he and his crew will want to do a good job, but he is not an experienced “green” contractor.
Thanks in advance for your input.
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