Roof Insulation Retrofit (Unvented roof)

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Adding exterior insulation to the roof of an old house is a great way to improve comfort and energy efficiency. It especially makes 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.

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 of 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, multiple layers of air sealing can turn a leaky old house into a 21st century home.


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