Chainsaw retrofit overhangs
I am rehabbing a 1900 farm house near Rochester, NY (Zone 5). We are replacing the roof, with much of it being restructured as well. Because of a mixture of cathedral ceilings, knee walls with sloped ceilings, and dormers, I am opting for a hot roof with two layers of rigid insulation (1-1/2″ + 3″ polyiso) on top of the sheathing and cellulose in the rafter bays.
In order to get a tight house and to reduce thermal bridging, I want to construct the new roofs without overhangs and cut off the rafter tails on the roofs that are staying. Then, the overhangs will be constructed afterwards.
My question is related to constructing the overhangs. My framer is recommending that 2×4 outriggers for the overhangs be added either directly to the roof deck, or on top of the first layer of insulation instead of on top of the full depth of rigid insulation. That way, the rafters will be easier to find and shorter screws can be used. The framer is insisting that the total R-value of the roof assembly will be minimally affected.
Is this safe? Am I risking the sheathing at those points dropping below the dew point? Repairing rotten sheathing on a hot roof is NOT something I want to do.
Thanks in advanced.
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