# Modelling 90.1 Baseline Envelope for Existing + Additions

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Dear forum users, I have modelled a project following Appendix G. and have
received a review regarding my interpretation of % glazed area on the
baseline.

The project is a mayor renovations + Additions (existing conditioned
warehouse + New office building attached). There were no modification on %
area of vertical and horizontal glazing on the existing bit of the building.

My approach was to model existing envelope, shape and fenestration, exactly
the same in both proposed and baseline. The addition was modelled following
the "maximum 40% for vertical fenestration and 5% for skylight" rule. The
result of the whole building for baseline is, 28% vertically glazed and 12%
of skylights (the existing bit was very different than 40%, and 5%
respectively)
The reviewer states that the end result for the baseline should still be
40% and 5%. It is not very clear to me how would I get there.. Do I have to
make the existing fenestration proportionally smaller, just like I would do
for the baseline of a completely new building?

Santiago.

Santiago Velez

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Proposed and Baseline areas/layouts matching works perfectly until you exceed either 40% for vertical or 5% for skylights. See Table G3.1.5, baseline items c. and d. This might be coincidence, but just to be cover all bases: 28% + 12% = 40% is an incorrect reading - the skylight and vertical fenestration thresholds are independent.

I think you are to leave the vertical fenestrations alone (being under the 40% threshold) and you need to proportionally lower the area of the skylights in the baseline model to get back to 5%. Proposed model needs to match actual design so it's skylights remain the same.

I'm not certain how or if the project being a major renovation has any bearing on the matter.

Are you making the case that the existing skylights are envelope components not being touched, and so should remain equal in area between the models despite exceeding the 5% threshold? Do you have additional new skylights complicating the matter?

NICK CATON, P.E.

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Nick, thanks for the response. The answer is yes, I'am trying to make a
case for exceeding the 5% threshold for existing bit of the project, which
is not modified.
The project is a big existing conditioned warehouse, with lots of skylights
(18% of roof area), the new bit is an office building, with more skylights
(properly shaded this time!). I thought it would be fare to have a baseline
which maintains the existing bit exactly the same (18% skylights), and the
new addition according to Table G3.1.5 (5%). The global skylight area for
the whole project is *12%*, and this was reviewed.
The opposite happens for vertical fenestration, warehouse has almost no
windows, and the new office is fully glazed. With the same criteria,
existing stays the same, new is 40% max; then the proposed ends up with
global 32% WWR and baseline only 28%. This was reviewed as well. Am
I explaining my self?

I thought this would be fair, and in fact it made so much sense I thought
it was the only possible interpretation... Its very good to remember one an
be *very* wrong.

So my approach should be:
- For vertical fenestration, 32% both baseline and proposed.
- For the skylights, I would multiple every skylight by 5/12 to get a
global 5% skylight.

Hmmm....energy savings are going to plummet.
Thank you again Nick.

Santiago.

2013/11/4 Nick Caton

Santiago Velez

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PS. : My interpretation was mostly based on *Appendix G Table 3.1.5 f)
"Existing Buildings. For existing building envelopes, the baseline building
design shall reflect existing conditions prior to any revisions that are
part of the scope of work being evaluated."*

2013/11/4 Santiago Velez

Santiago Velez

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Santiago,

I would reach out to the reviewer and argue that your original
interpretation is correct. Appendix G Table 3.1.5 f that you quoted below
clearly suggests that the baseline building design for renovation projects
shall reflect existing conditions prior to any revisions. The section covers
all aspects of envelope including thermal and solar properties, assembly
type, and surface area, so there is no indication that the "existing
conditions" mentioned in 3.1.5 f exclude fenestration / skylight area. I
don't see why this rule should be void for projects that include both
Limits. When the proposed modifications apply to less than the whole
building, only parameters related to the systems to be modified shall be
allowed to vary. Parameters relating to unmodified existing conditions or to
future building components shall be identical for determining both the
baseline building performance and the proposed building performance. Since
the window/skylight area is not modified, it should produce neither penalty
nor credit for the proposed design.

Maria

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Joined: 2011-09-30
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Maria thanks for sharing your opinion. I will reach out to the reviewer.
It's good to know there can be different interpretation. I do understand
that if you are certifying as "New construction and Mayor renovations" it
might make sense that you need demonstrating savings against the full new
Baseline defined by Appendix G. It would be nice if future editions of the
grey areas.

Thanks.
Santiago.

2013/11/5 Maria Karpman

Santiago Velez

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I also agree with Maria's input. When existing conditions are known, those should supercede the baseline requirements set up for to address new construction.

I've experienced a grouping of major renovation LEED projects where the reviewer in fact pushed me to document and model actual existing opaque envelope constructions instead of the standard baseline constructions, which actually boosted the performance ratings quite a bit. This was simple on my part as I already had the needed information worked into my proposed model.

In making your case with your reviewer ahead of time (which I'd reinforce as sound advice) and for your model documentation moving forward, I advise clearly and separately documenting the area totals for skylights and roof areas between the existing/untouched portions of the building and the new areas of the building. As you originally posed the question to the lists, we had to speculate in that direction.

NICK CATON, P.E.

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I will do that and then post back when this is settled to share the
experience and keep building this virtual knowledge base.
Thanks again.

2013/11/5 Nick Caton

Santiago Velez

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