Building rotation per Appendix G

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I'm working on a project where I am pursuing LEED EAc1 for an existing
building. As I understand it from the LEED-NC reference guide, as well
as from some snippets of 90.1, I actually model the baseline building as
is currently exists. The reference guide says:

"For existing buildings that are being renovated, the building envelope
design parameters for the Baseline Design should be modeled using the
existing (pre-retrofit) building envelope thermal parameters rather than
the ASHRAE 90.1 prescriptive building envelope requirements for the
specified climate."

So I'm using actual window areas, actual insulation values, etc.

My question is: if I'm using this exception, do I also no longer have
to do a simulation at the four different azimuth required by the LEED
EAc1 template?

I find 90.1, as well as the user's manual, fairly lacking in describing
how to apply Appendix G to existing buildings in general....

Thanks in advance!

James Hansen, PE, LEED AP

James Hansen's picture
Joined: 2011-09-30
Reputation: 200


It is my understanding that it is not necessary to do the rotation on an
existing building. I am also working on an existing building, and I
plan to submit without rotating. This topic has been debated on the
forum in the past with opposing opinions, each side having reasonable
arguments, but if my memory is correct the best/last argument was that
existing buildings do not need to be rotated. I think this position
makes more intuitive sense, too.

I don't believe a definitive resource exists for this question, which is
why I plan to "learn the hard way" on my project. I have heard that
2009 LEED revisions will address questions specific to existing
buildings; hopefully this will be one of them. In the interim, I would
ask that anyone with a differing opinion specify the resource guiding

Dakota Kelley

Dakota Kelley's picture
Joined: 2011-09-30
Reputation: 1

What if it is an existing building and there have been alterations to the

Kevin Kyte's picture
Joined: 2011-09-30
Reputation: 0


I have since reversed my stance; Eric O'Neill was kind enough to provide
me with the following link:

I had not come across this thread before, and it sounds like existing
buildings need to be rotated regardless of the situation.


Dakota Kelley's picture
Joined: 2011-09-30
Reputation: 1


I asked a question a few weeks ago about whether or not you have to rotate the Baseline building in a LEED-NC EAc1 calculation (or Appendix G calculation for some other reason). Thank you everyone for your replies (see below) appears that yes, you do need to perform the four (4) separate runs for each direction.

However, I have a more general question about modeling renovations to existing buildings. According to the LEED-NC reference guide, you are to model the Baseline building (if it is existing) with the same "thermal parameters" as the existing building. Appendix G, Table G3.1 Section 5f) says that "For Existing building envelopes, the baseline building design shall reflect existing conditions prior to any revisions that are part of the scope of work...".

Futhermore, the reference guide goes on to say that "For projects served by existing HVAC systems, such as a central plant on a campus, Section 10(a) of Table G3.1 states that when there is an existing HVAC system, the model shall reflect the actual system type using actual component capacities and efficiencies."

But this section is actually under the "Proposed" column, and I can't find anywhere where it specifically says that the Baseline system should be modeled as the existing building currently stands.

So I have two questions:

1) If you have an existing building, is the HVAC system supposed to be modeled as it currently exists in the Baseline model, as well as things like the thermal parameters, etc? What about the lighting? If you have an existing building that you KNOW has a lighting density of 2.0 Watts / sq ft pre-retrofit, is that how you should model the Baseline building?

2) If I have an existing building that happens to have one exposure with NO windows, and part of the renovation is to install windows on that side of the building, while STILL BEING BELOW 40% total window area. How do I model the baseline building? With windows there or not? If not, then that is a major penalty, and in reality, I may want to compare my Proposed building to a Baseline model that is 90.1-2004 compliant. Can you even do that if it is an existing building? Can you choose whether to model the Baseline building it as it exists, or model it per minimum ASHRAE standards?

I haven't yet received a copy of 90.1-2007. Does Appendix G in that version clarify any of this?

Thanks in advance!

James Hansen

James Hansen's picture
Joined: 2011-09-30
Reputation: 200