#1402 Raised Heel Truss - ACM & Software Language Update

[Trevor Thomas]

Email from Luke Morton asking if we can remove/adjust the 'Truss' language:

I got a report from a plan checker on a project that is taking issue with the consultant taking credit for 'raised heel truss' since the attic is not framed with trusses but conventional framing.
In short-- the plan checker believes that the attic must be framed with trusses in order to qualify for the credit. It's perhaps a silly semantic question, but I can't fault the plan checker for taking issue.
The software allows for the credit to be taken even though conventional framing is used, which is entirely reasonable.

However, going to the ACM, it looks like everything in there refers to 'trusses' (Section 2.6.5) so the software is reflective of that.
And the report indicates 'Raised Heel Truss' as a special feature.
Reviewing the Appendix G algorithms-- 2.2.2.3-- there doesn't appear to be anything specific about the underlying algorithms which would preclude it from applying to conventionally framed raised heels.

Recommendation: I think it's prudent to remove the 'truss' everywhere here-- I can't see how it's relevant. A raised heel is a raised heel regardless of how it's constructed (on site, or as a prefab truss system). Technically, this should be removed from the ACM and then can be removed from the software, but I don't see the word 'truss' in the ACM being a substantive descriptor, so it would be good enough to revise the software and report to say 'raised heel' or 'raised heel at attic edge'

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ACM section below
A raised heel truss (Figure 10: Section at Attic Edge with a Raised Heel Truss) provides additional height at the attic edge that, depending on the height Y and the ceiling insulation R, can either reduce or eliminate the attic edge area and the associated thermal effect.

For cases where the depth of insulation (including below-deck insulation depth) is greater than the available height at the attic edge, the compliance software automatically creates cathedral ceiling surfaces to represent the attic edge area and adjusts the dimensions of the attic air space using the algorithms contained in Appendix G. If above-deck insulation is modeled, it is included in the attic edge cathedral ceiling constructions, but radiant barriers below the roof deck are not.

Proposed Design
The compliance software shall allow the user to specify that a raised heel truss will be used (as supported by construction drawings), with the default being a standard truss, as shown in Figure 9: Section at Attic Edge with Standard Truss. If the user selects a raised heel truss, the compliance software will require the user to specify the vertical distance between the wall top plate and the bottom of the roof deck (Y in Figure 10: Section at Attic Edge with a Raised Heel Truss).

[Trevor Thomas]

Will not be making any changes to this.