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Community and Q&A

Thermal bridge and raised-heel truss

Ryan Campbell | Posted in Green Building Techniques on
I’ve been trying to find information on heat loss through the truss overhang. The most recent post here was from 2014: https://www.greenbuildingadvisor.com/question/thermal-bridging-at-overhangs, with a suggested solution of applied overhangs: https://www.greenbuildingadvisor.com/article/airtight-wall-and-roof-sheathing. This brings up a few questions:
1. Considering how few people talk about this online, is the heat loss minimal?
2. Going with applied overhangs would force an unvented roof, which there is plenty of debate around. Would the continuous insulation gains offset any unvented roof concerns?
3. Is it worth insulating underneath the rafter tails so that the heat has to travel further out of the fascia?
4. Somewhat unrelated, but some illustrations show the attic insulation going past the studs and being held in by baffles (http://www.prairiedesignbuild.com/blog/2014/8/19/thermal-bridging), while others just run the exterior wall insulation and sheathing up to the roof sheathing. Is there a consensus?
I appreciate any tips or advice. Thanks!

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Ryan,
    The heat loss through the path you are talking about is minimal. If you want this area to be well-insulated, (a) make sure that your trusses have a deep enough heel for your insulation target (R-49 or R-60, probably) plus two inches for your baffle plus ventilation gap; (b) make sure that the attic insulation covers the entire top plate of your exterior walls.

    1. Ryan Campbell | | #2

      Perfect, that settles it. Thanks again.

  2. Akos | | #3

    Ryan,

    If I read your drawing correctly, it shows a vented assembly with exterior insulation on-top of your roof. Exterior insulation doesn't do much for a vented assembly, pretty much wasted $$.

    Also, if you are blowing in insulation, it will be a lot cheaper to blow in an extra 3" above the Intello than installing the rockwool batts between the strapping.

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