Replies

1. 
   user-1135248 | May 17, 2014 05:36pm | #1

   Wouldn't that depend on how you intend to tie all that to the
   wall assembly? The insulation layer should be as contiguous
   as you can manage, I would assume. The typical roof/wall junction
   is a squeeze area subject to a lot of thermal bridging, probably
   not an area to skimp on.

   You might want to delete your duplicate post [if that's
   possible..] so answers accumulate in one place.

   _H*

2. 
   user-2385486 | May 17, 2014 07:17pm | #2

   Hobbit,
   There shouldn't be much thermal bridging-the dense pack will cover the top plate and so at the exterior wall the insulation line would be a nearly continuos stack: wall insulation(cavity fill and exterior foam) then dense pack over the plate then foam over the first layer of roof sheathing.

   You are getting at the heart of my question though. Is there any benefit (to mitigating thermal bridging or possible areas of condensation) to having insulation outside the building line that is not insulating the conditioned space directly

   I'll try to delete the duplicate post, thanks.

3. GBA Editor
   Martin Holladay | May 18, 2014 06:43am | #3

   Stefan,
   In some climates, solar radiation on the south side of the building can heat the south-facing siding, and cause a pocket of warm air to form under the soffit on sunny days. This pocket of warm air can encourage snow on the roof to melt at the eaves, leading to ice damming. If you continue your rigid foam all the way to the eaves, the added insulation can reduce ice damming under these circumstances.

   Of course, if you live in a climate where ice damming isn't an issue, this concern doesn't apply.

   If you omit the rigid foam at the eaves and rakes, you still have to install shims to support the top layer of sheathing and roofing. It's usually simpler to just extend the rigid foam to the edges of the roof.

4. 
   user-2385486 | May 18, 2014 07:35am | #4

   Thanks Martin.
   I live in a Zone 4 climate north of Seattle, with little/no snow accumulation. The gable and eave overhangs are a bit more than 3', equaling about 35 extra sheets of foam at 2 layers. Financially/material use wise it makes sense for me to leave these out. So other than the ice dam concern, are there any other reasons to insulate this area?

5. GBA Editor
   Martin Holladay | May 18, 2014 10:00am | #5

   Stefan,
   Q. "So other than the ice dam concern, are there any other reasons to insulate this area?"

   A. No.

6. 
   user-2385486 | May 18, 2014 10:31am | #6

   Thanks for your help.