Situation: Garage near San Jose, CA. Old part and new part. Old part (1962) with simple gable roof. It has skip sheathing. New part (1988) built as addition off the back with plywood sheathing. Ridges are perpendicular, making 2 valleys where the old and new roofs come together.

I’m tearing off the roofing and will be putting OSB over the skip sheathing, and laying new comp shingles.

Question 1: How much gap is reasonable in the valleys between the sheathing of the addition and what I’m putting on? Some of the cuts on the existing sheathing are pretty curvy and it might be hard to meet the cleanly. It looks like they just cut back the existing shingles on the old roof, built the new roof on top of the part of the old roof they had exposed, and then bridged the valley with felt and shingles; no metal.

Question 2: I understand that the long edge of the new sheathing has to fall on a skip sheathing board, but I’ve heard two things about the short end (the “vertical” ends, parallel to the rafters). One contractor told me that, with the sheathing there, I don’t need to cut the sheets to end over a rafter (handy since they didn’t seem all that careful to make the rafters *exactly* spaced in the pre-plywood days, so I’d have to cut every sheet by an inch or two to make them land exactly over a rafter. On the other hand, a building inspector (not mine) said I *must* end over the rafters, even if there are skip sheathing boards underneath. Is there a clear answer, or is it dependant on the local city or, worse, the individual inspector?

Question 3: will 8d nails be OK for nailing the OSB over the sheathing?

Thanks for your help!

-- Rich

 

Last time I tried breaking the joints on the rafters, the unevenness of the sheathing boards caused the osb to be uneven.
So, I broke them 'near' the rafters. All osb was screwed 4"oc on edges and into all rafters.