Covering the roof of an old house with a blanket of insulation makes the house more comfortable and it cuts energy use.
It makes a lot of sense if the rafter cavities are already insulated, and it is most affordable when the roof needs replacement.
- The first order of business to to strip the roof.
- Next, cut off the rafter tails so that the connection between roof and walls can be sealed with peel and stick membrane.
- Dry in the roof with peel and stick membrane
- Install two layers of insulation to the roof, staggering the seams, offsetting the joints, and taping outer layer. Extend the foam 4 inches past the walls, so that you can add foam to the walls later and tie it in to the roof.
- New roof sheathing on top can extend out to create a new roof overhang.
- It is held in place with screws that reach 1-1/2 inches into the framing.
- On top pot the sheathing, install a waterproof, but vapor open roofing paper to avoid trapping moisture between it and the peel and stick.
- Box out a soffit and tie it all together with fascia.
Continuous insulation and multiple layers of air sealing can turn a leaky old house into a 21st century home.
2012 IECC: SECTION R402 BUILDING THERMAL ENVELOPE