90.1 Baseline Envelope Interpretation

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Hi All,

I am having trouble fully comprehending ASHRAE 90.1 Appendix G, referring to existing building envelopes. The building I am modeling was previously a maintenance shop with practically zero insulation. In addition to the basic building envelope, the southern facing exposure is essentially 4 large garage doors.

The entire envelope was gutted and replaced with a brick/concrete wall and corresponding insulation. In addition to the envelope upgrade, the entire interior was remodeled to be utilized as an office building. Appendix G leads to me to believe that I should be modeling the building envelope as if the garage doors are still in place. i.e. the offices will have a garage door modeled as the wall type with a significant amount of infiltration. This seems counter-intuitive to me, but I want to verify that I am doing it correctly.

Any input would be helpful, Thanks.

Daniel Kaler

Daniel Kaler's picture
Joined: 2011-12-01
Reputation: 0

Hey Daniel,

Hmm - I have never been called out one way or the other regarding existing envelopes under formal review so I can't say with certainty... I'll agree your situation seems tricky!

There's a line within Table G3.1, section 5 baseline column, that also reads "Opaque assemblies used for alterations shall conform with Section 5.1.3." "Alterations" is a vaguely written glossary term which could be read to apply to your wall upgrades as described.

5.1.3 broadly says all requirements in section 5 for insulation, air leakage and fenestrations apply to the alterations.

Reading that together with G3.1.5.f, your baseline alteration walls should reflect the pre-existing building envelope in every regard, excepting any prescriptive/mandatory requirements of section 5 regarding insulation, air leakage and fenestrations... This assumes none of the 5.1.3 exceptions apply. This interpretation would permit things like WWR and infiltration rates to differ from the proposed envelope.

I would not advise going hog-wild with differing infiltration rates however. Garage doors may generally leak more than the proposed construction - but use and document conservative numbers that make sense for an "always closed" door (with weatherseal if applicable) per the mandatory infiltration requirements. If you assume the baseline doors are regularly opened by mechanics in the baseline, you're straying from the "same occupants, same scheduling" theme repeated through the rest of Appendix G.

Hope those thoughts help!


[cid:489575314 at 22072009-0ABB]


Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805

Nick and Daniel,

On a high level, Appendix G baseline is a virtual building configured as
described in Appendix G and compliant with requirements of 90.1 applicable
to this configuration. In order to comply with 90.1, major renovation
projects are generally not required to retrofit envelope so that it meets
the current requirements of ASHRAE 90.1, which explains provision of
G3.1.5.f to use existing envelope in the baseline. However, when renovation
involves change in space conditioning category, e.g. an old semiheated
warehouse is converted into an office building, 90.1 requires that all
systems including envelope are brought into compliance with the current
provisions: Changes in Space Conditioning. Whenever

unconditioned or semiheated spaces in a building are converted

to conditioned spaces, such conditioned spaces shall

be brought into compliance with all the applicable requirements

of this standard that would apply to the building envelope,

heating, ventilating, air-conditioning, service water

heating, power, lighting, and other systems and equipment of

the space as if the building were new.

It looks like Daniel's project is subject to this requirement. I don't know
what's LEED policy on that, but a few modeling-based incentive programs that
I am involved with do not allow using existing condition as envelope
baseline for projects that involve changes in space conditioning. Otherwise
they get incentive windfall for doing what they are required to do in order
to meet energy code (in states where energy code is aligned with 90.1). For
a LEED project, I would make sure that systems other than envelope (e.g.
HVAC, lighting, etc.) are efficient enough to meet EAc1 target in case
envelope baseline is questioned by LEED reviewers.



Maria Karpman's picture
Joined: 2011-09-30
Reputation: 0