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October 31, 2018
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From NGA's Department of Advocacy & Technical Services:

ASHRAE 90.1 Update
I wanted to send out a quick update following the ASHRAE 90.1 committee meeting just held in Atlanta. There were three items of interest to us, and all good news:

Window Criteria Proposal
As reported previously, the comprehensive update to the fenestration criteria (U-factor and SHGC for windows, entrance doors, and skylights) that we have worked on for the last year went out for public review as Addendum AW. This affects residential multifamily buildings 4 stories and higher, as well as commercial buildings. This proposal provides an increase in stringency while still being cost effective and practical, and also aligns the product categories to match those used in the IECC without regard to material type. The proposal received 3 supportive comments (NGA, RECA, WDMA), and 4 comments requesting small corrections (AAMA, WDMA, Velux). We knew those were coming in, and the good news is that there were no unexpected negative comments from out of left field.

At this meeting, we successfully convinced the committee to make those corrections in response to the comments: (a) adjusting the residential skylight U-factor in zone 6 from 0.47 to 0.50 to account for unit skylights on curbs; (b) adjusting the fixed SHGC in zone 5 from 0.36 to 0.38 to better accommodate curtain wall framing systems in addition to window wall, storefront, and unit windows; and (c) adjusting the U-factors for skylights in semi heated spaces (e.g. warehouses) up in zones 2-8 following review to include more product options. Just these limited changes will go out for public review, and assuming there are no more comments, the addendum will go up for final approval at the January meeting.

Thermal Bridging Proposal
The big proposal to address thermal bridges that bypass wall, roof, and floor insulation also completed its public review. The portions that potentially affected us involved rules on the intersection between window framing and the opaque wall, limitations on attachment area for sun shades, and how thermal bridges could be traded off against wall and window performance. But the proposal is much bigger than just that, also affecting structural areas like balconies, parapets, canopies, etc. It has been very controversial, and the proposal received nearly 250 negative comments. Many consider thermal bridging as an important issue, but because it has the potential to negatively impact structural performance, feel that it is better addressed in design guides rather in a code. Because of the unusually large number of comments, the subcommittee is trying to figure out whether to continue with it at all, and if so, how to fix it. This clearly means it will not make the 2019 edition, if it continues at all.

Envelope Backstops
The other area I have been concerned with are “envelope backstops” or limitations on trade-offs when using the performance path. This limits product flexibility, and most importantly, could be used to limit window area in office and high-rise residential buildings even if you show equivalent or better energy performance – obviously a big red line for us. I’ve been participating with the workgroup where these proposals are coming from, and three different approaches have been suggested. It’s in the nerdy details, but let me know if you want info on the concepts. It’s a big issue that I don’t want rushed into the 2019 edition, and the good news is that the subcommittee agreed. No action was taken, and they will spend more time to discuss and carefully analyze the potential impacts. This means that if they develop something, it would not be in the standard until 2022. This will hopefully also help stop premature backstop proposals at the IECC hearings next year.

That’s the short version—contact me at if you need more details or if you have any questions.

Best regards,

Thomas D. Culp, Ph.D.
Birch Point Consulting LLC
La Crosse, WI

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