Exterior Roof and Wall Insulation Retrofit (Unvented Roof)

October 28, 2015

 

Wrapping an old house in a blanket of insulation is a no-brainer when you're replacing the roofing and siding anyway

 

Adding exterior insulation to the roof and walls of an old house can improve comfort and energy efficiency. 

It especially makes sense if the rafter cavities are already insulated, and it is most affordable when the roof and siding need replacement. 

 

Step-by-step:
  • The first order of business is to strip the walls and roof.
  • Next, cut off the rafter tails so that the connection between roof and walls can be sealed with peel and stick  membrane.
  • Cover the roof with a waterproof barrier or membrane.
  • Install two layers of foam to the roof, staggering the seams, and offsetting the joints, and tape the seams on the top layer.
  • New roof sheathing goes on top screwed into the framing an inch and a half
  • Cover the roof deck with roofing underlayment that will protect against liquid water, but allow vapor to escape.
  • At the bottom of the wall, bend a piece of coil stock into a J channel to keep the bugs out. The metal is tucked behind the house wrap. 
  • Two layers of insulation go on the walls with the outer layer’s seams taped for an air seal.
  • Attach a strip of bug screen to the bottom of the wall to keep the ventilation channels clear.
  • At the corners, weave the foam panels together to disrupt clear air paths between inside and out.
  • The corners are then wrapped with peel and stick to meet them tight
  • Furring strips are screwed to the foam an inch and a half into the framing. 
  • The furring provides ventilation space and a solid base for siding. 
  • Box out a soffit at the top of the wall and tie it all together with fascia.
  • Install the siding, making sure to detail the bug screen tightly at the bottom of the wall.

Continuous insulation, multiple layers of air sealing, and ventilation channels turn a leaky old house into a 21st century home.

 

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2012 IECC: SECTION R402 BUILDING THERMAL ENVELOPE

2012 IRC: SECTION R806 ROOF VENTILATION | SECTION R906 ROOF INSULATION

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SLIDE SHOW AND DOWNLOAD

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