Butt these against the bottom of the old roof s third row and nail into place.
Framing a new roof over an old roof.
Installing the new roof.
You can frame a new roof over the old but it will need to be designed for the span and pitch.
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.
Your second row of shingles should be cut to 10 inches wide.
The sheathing must be stripped from the old roof for a couple feet along the bottom to get the new ceiling joists in.
Use 1 5 or 1 75 inch roofing nails.