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Truss heel dimension

Trevor_Lambert | Posted in General Questions on

I’m getting ready to order some roof trusses. and I noticed that the dimension they show for the heel of the trusses is 1-3-9. I’m guessing from context clues that’s feet-inches-16ths. I hate the imperial measurement system, but that’s another story. My drawings specify a heel of 1’6″. I then noticed that on the truss drawing, it looks like the heel of the truss is sitting on two 2x4s. I don’t know whether that’s supposed to represent the wall double top plate, or additional pieces above the top plate, or what. Is this a standard way of building up the heel height?

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Replies

  1. Trevor_Lambert | | #1

    I'll try to upload images here.

  2. Expert Member
    Michael Maines | | #2

    Conventions may vary but in my experience the double top plates are just showing where the truss is supported. In your case, they are treating the interior wall as the bearing wall. Is that your intention? The heel height is typically measured at the exterior face of the wall, so 1'-3 9/16" is the height there, and it's probably 1'-6" at the exterior face of the supporting wall.

    Double-stud walls are not typical, and using the interior wall as bearing is less common than using the outside wall as bearing, so the drawings you provide them need to be extra-clear. It's perfectly fine to respond to them with changes or questions.

    **Edit: somehow I missed your drawing and only looked at the truss drawing. It appears that they made a mistake on the heel height; their software probably assumes the heel height is at the vertical support. Just tell them that you want the 1'-6" measured as the outer face of the exterior wall and you should be good to go.

  3. krackadile | | #3

    The two 2x4s that the drawing shows under the heel of the truss is intended to represent the wall the truss is sitting on, typically a 2x4 double top plate.

    So, the truss heel height is the vertical distance between the top plate of a wall and the underside of the roof sheathing, measured at the outside wall. The dimension you see that is 1-3-9 appears to me to be where the vertical member in the truss connects to the rafter. So, the heel height would be the 1-3-9 dimension plus the thickness of the rafter in that location, which should be around 3.5" for a total of around 16-17" for your heel height. It does not appear that the heel height was dimensioned in your truss shop drawing.

    If it were me I would just call the manufacturer or supplier to confirm prior to placing the order.

  4. GBA Editor
    MALCOLM TAYLOR | | #4

    Trevor,

    Another small difference is that yours showed a continuous bottom chord out to the overhang, while theirs uses the more conventional layout where you would have to frame the soffit. Yours would make running the soffit material parallel to the house easier, but harder if it goes from the rough fascia to the wall. Theirs lets you to use a shallower fascia, and allows you to run the sheathing up to both contain the insulation, and as bracing.

    1. Trevor_Lambert | | #5

      The continuous bottom chord was removed in a revision, for which I couldn't find a drawing. It might have just been a note somewhere along the line.

      1. GBA Editor
        MALCOLM TAYLOR | | #6

        Trevor,

        I am surprised the bracing schedule is so lenient. The standard note for the bottom chord, and nothing to compensate for the lack of sheathing.

        1. Expert Member
          Michael Maines | | #7

          Malcolm, I had mentioned recently that our truss designs in New England don't have much bracing info. We typically get a single sheet that looks just like Trevor's, and sometimes a boilerplate sheet in addition. No custom bracing schedules.

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