Unvented vaulted roof/ceiling
I’m retired and disabled and therefore have a tight budget to build an addition onto my
house, a small apartment to accommodate a caregiver for myself. Some friends are
building it for me and I hired a local guy. We built a stone and cement
foundation with forms and used 3×8 fir for joists, insulated in between using
chicken wire to hold up fiberglass bats and vapor barrier.
The floor is flush 2×6 t&g fir and I had some 8×8 larch timbers I’ve had for 15 years which
were cut from ancient fire killed snags. These are the uprights at 3 and 6 foot
centers (6 foot for windows).
We used 4×8 fir for a plate and 4×8 fir for roof rafters on 3 foot centers. The span is 14 feet, For both roof deck and ceiling we used 2×6 t&g spruce covered with 30 pound building paper (felt). It is a simple shed roof and I have duraclad 36″ (5 ribs) metal roofing to apply. 2×4 strapping has been attached and I have styrofoam insulation to fit snuggly between them and then on goes the roofing. The square footage is around 350.
My question is related to venting the roof. I have read that it is best to completely seal this configuration of vaulted roof rather than attempt to vent it. If we are going to seal it, should we spray foam insulation around the edges so as to seal the ribs and all in the metal roofing? Or are the ribs alone enough to be considered ventalation?
We do have an option to place a solid sheet of 6 mil vapor barrier over the felt and strapping prior to the styrofoam and metal. I’m not so sure it would be a good idea to seal the strapping like this. Alternatively we could put the vapor barrier only between the strapping over the felt.
The ceiling will be coated with verathane.
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