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Building Science

Raised-Heel Trusses Make Better Enclosures

This is another easy advanced framing technique for every home with roof trusses

Raised-heel trusses make better enclosures by allowing for more insulation above the exterior walls.
Image Credit: Image #1: The Engineered Wood Association

A comfortable, energy-efficient home begins with a good building enclosure. That means control layers. You’ve got to control the flows of moisture, air, and heat.

Today, let’s talk about controlling heat and further. Let’s focus on heat going through the top of the house. If you’ve read my Flat or Lumpy article, you know it’s better to have a uniform coverage of insulation rather than a lot of insulation in some places and little insulation in others. But you may not know about one place where many homes just can’t get enough insulation.

Yep. I’m talking about the space over the exterior walls, where the roof comes down and leaves little space for insulation. Take a look at the Image #2 below. It’s from the .

The trusses seem to be made from 2x4s, so there’s about 4 inches of space for insulation over the exterior wall (at the bottom of the photo). The rest of the attic will have about 12 inches or more of blown insulation. Hmmmm. Is there some reason that the space over the exterior wall might have lower susceptibility to heat loss and heat gain? In summer, it could be a bit cooler there because of venting (not shown). In winter, that spot is likely to be worse than the middle of the attic, again because of venting. Overall, though, there’s not good reason to have less insulation there.

And speaking of venting, check out Image #3, a Building America photo showing incorrect installation of the baffles. The problem there is that the cardboard baffles are stapled to the inside of the top plate. In this house, as a result, there’s going to be absolutely no insulation directly…

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  1. Jon R | | #1

    Also note that you can get a
    Also note that you can get a raised heel scissor truss - providing a vaulted ceiling with the cost, energy and moisture advantages of a vented attic.

    If you don't have a raised heel - insulation in a tray ceiling would add insulation to the ceiling perimeter.

  2. Malcolm Taylor | | #2

    Raised-heel trusses in high seismic zones
    There are two downsides to raised-heel trusses.
    - Like scissor trusses, they are harder to set as the heel makes them unstable.
    - In high seismic zones just running the sheathing up to the top chord doesn't provide enough shear strength. Small shear panels need to be build between each truss.

    Neither are that big a deal, but do add to the time and expense of the roof.

    Edit; Jon makes a good point about ceiling trays or bulkheads.

  3. Rob Hunter | | #3

    Another variation
    If you extend the scissor truss over the sidewall with an 18-24" overhang, you'll get the equivalent of a raised heel truss with nice options for fascia and gutter trim. Truss design needs to accommodate the load point, of course... but not difficult or particularly expensive. I suspect @Malcolm Taylor's shear panels can also be mostly outboard of the wall framing with this design. But yes, it makes sealing the attic space for an unvented roof more challenging; I'm still sorting out that detail. [Ideas welcomed!]

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