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Exterior Roof Insulation Retrofit (Unvented Roof)

October 15, 2015

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. 

Step-by-step on continuous exterior roof insulation:

  • 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.



2018 IRC: 



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