George, a homeowner in Massachusetts, had this question about his roof:
We have an old roof (135 year old house) with skip sheathing. Gaps are not big but probably over a quarter inch in places. The last time the roof was shingled (before we bought the place) they shingled directly onto the skip sheathing; no plywood. Now we have to add plywood everywhere (half inch CDX) overbite skip sheathing. The question is what do we nail the plywood in to: the skip sheathing or the rafters underneath, or both. If we have to nail the plywood into the rafters how do we do that? A chalk line, but how accurate will that be. This is urgent so looking forward to hearing from you.
The plywood should be nailed to the rafters. The nails should be long enough to reach through the existing skip sheathing and into the rafter.
Mark the rafter location on the plywood as you lay it out. Use your chalk line to aid in nailing into the rafter. There is not a better line to follow than a straight chalk line. If the rafter is not straight, adjust. You will feel it if you miss the rafter. Hand nailing or gun nailing, you will notice a difference.
Sounds like a “Fun” project. Let us know how it turns out.