Old Roof New Roof Joined Rafters

Cut two rafters with a circular saw to the pitch of the addition roof and nail them across the rafters on the old roof.

Old roof new roof joined rafters.

Install bent metal flashing where the old and new roofs meet and on the peaks and metal drip edges along the eaves. You ll need to install a valley board or nailer over the old roof shingles to create a solid nailing surface for installing jack rafters see drawing. Then set one new truss in place against the old roof and use it to snap chalk lines to mark the location on the old roof for diagonal 2 inch by 6 inch valley boards which will hold jack rafters to tie the roofs together. Installing a new roof over an existing one also called a layover or nailover is often possible although not always the best option.

Remove shingles and other roofing material where the new roof will join down to the deck board of the old roof. Cover the roof with roofing paper overlapping seams generously then nail on shingles. A new level 2 6 ridgeboard and rafters then are assembled over the old roof and are attached to the existing structure with nails and lag screws driven into the underlying wall top plates. A properly installed layover roof can look and function as well.

Nail oriented strand board osb decking over all the new rafters.