Closed cell polyurethane foam insulation is sprayed around the new roof frame sealing edges and providing support for the rafters and the ridgeboard.
Framing a new roof over an old roof.
Or if you want to raise the roof a bit more install fascia around the roof perimeter attached to the new soffit and nail the new roof deck to crown molding above the fascia.
You can frame a new roof over the old but it will need to be designed for the span and pitch.
To provide a framework for the new trusses nail 2 by 6 inch strips of wood around the perimeter of the roof.
The sheathing must be stripped from the old roof for a couple feet along the bottom to get the new ceiling joists in.
Butt these against the bottom of the old roof s third row and nail into place.
Your second row of shingles should be cut to 10 inches wide.