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Wall boundary condition when abutting an adjacent building

asked 2015-04-23 10:39:34 -0600

updated 2015-07-11 20:03:38 -0600

I'm wondering how people have been treating the walls between the modeled building and any adjacent buildings it's abutting in the proposed design, when doing New Construction.

For EB and retrofit, there's no question, I'll treat it as adiabatic, unless I have thorough reasons to believe the next door building is or will be soon empty or even knocked down.

For New Construction, I'm a little bit more confused, especially considering you're supposed to rotate your building for the baseline...

If I were to go crazy down that path: if I treat it as adiabatic, does this mean I'd have to rotate the building manually, see what end ups in contact with the adjacent building, and remove the windows there, while setting the former adiabatic portion to exterior wall?

Here's an example of a project I'm working on right now:

My building is abutting three buildings

So what say you, fellow modelers?

  • Do you treat it as adiabatic? If so, do you include that wall in calculating the Window to Wall Ratio?
  • Do you rotate the building?
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answered 2015-04-23 14:57:01 -0600

keb's avatar

updated 2015-04-24 11:20:45 -0600

90.1-2010 Table G3.1.5a (Baseline) has two new exceptions regarding the requirement for providing rotational baselines, the first of which appears reasonable/invoked in your situation: "If it can be demonstrated to the satisfaction of the Program Evaluator that the building orientation is dictated by site considerations."

I think since you're latching an addition onto an existing building, this is the kind of site condition(s) referenced in the exception's verbiage.

That said, "demonstrat[ing] to the satisfaction of the Program Evaluator" seems to invite wiggle room and provides an opportunity for the Program Evaluator to resist for the sake of doing so.

If this exception wasn't provided in Table G3.1.5a, I'd defer to rotating the city block. :)

To answer your comment below: I say yes, set any wall area that is common to an existing building as adiabatic (assuming you satisfy items in Table G3.1.2a-d), and yes, include the adiabatic areas in the WWR calc. My reasoning is based on the fact that the language in 90.1-2010 Table G3.1.5c (Baseline) seems resolute: "...gross above-grade wall area". I think your plan East wall would have a max WWR of less than 40% due to adjacent geometry, and your plan South walls and (one) West wall would have a max WWR of zero assuming those adjacent buildings are at least as tall as your addition.

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Thanks Kent. Could you confirm you'd treat the walls as adiabatic too? If so, do you count it in the window to wall ratio calculation?

I appended my question to include a picture and the WWR ratio calculation question, since it doesn't warrant an extra question. I hope you won't mind that I did that after you answered

Julien Marrec's avatar Julien Marrec  ( 2015-04-24 01:29:10 -0600 )edit

answered 2015-04-28 14:05:27 -0600

I agree with Kent for the most part, and that's why I accepted his answer.

But as far as including the adiabatic areas in the Window to Wall Ratio (WWR), I would tend to disagree, though I don't have hard facts to support this.

One thing to note is that when you see a wall to adiabatic, softwares such as eQuest will remove it from the wall area and windows+wall area.

Though I agree you could take the "gross above-grade wall area" the way you want it, this wall is made adiabatic for a reason: it's abutting an existing building. My guess is that the intent was to mean the "gross above-grade wall area that is available to install windows (= that has a view)".

There might be a Credit Interpretation for LEED somewhere on the matter, or a request to ASHRAE for clarifications?

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Julien, I had those thoughts also regarding the adiabatic wall area in the WWR calc, and the "gross wall area" but chose to strictly interpret the black and white as opposed to putting words in the mouth of the technical committees haha. A request for clarification might be in order, yes. This apparently can be done by emailing the Manager of Standards at ASHRAE here. Not sure if you can wait 30 days for a response vs your timeline. I don't find related interpretations yet.

keb's avatar keb  ( 2015-04-28 14:50:19 -0600 )edit

I asked the question on bldg-sim, didn't produce a massive interest, but Nicholas Caton did offer a clear answer here, where he says he would exclude the adiabatic portion out of the WWR calculation.

Julien Marrec's avatar Julien Marrec  ( 2015-05-04 09:46:37 -0600 )edit

I have this same issue on a current project. To add to the discussion on the 90.1-2010 definitions: "wall: above-grade wall" is defined as a "that portion of the building envelope..." and "building envelope" is defined as separating conditioned spaces either from the exterior or from unconditioned space. Based on this, I agree that the adiabatic walls should be excluded from the WWR calculation.

Molly Curtz's avatar Molly Curtz  ( 2016-10-18 14:58:21 -0600 )edit

answered 2015-04-23 10:49:58 -0600

"The road to (LEED) hell is paved with good intentions." -St. Bernard. I say rotate the entire city block along with your building.

Disclaimer: I'm not a "fellow modeler".

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Asked: 2015-04-23 10:39:34 -0600

Seen: 1,374 times

Last updated: Apr 28 '15