existing envelope CIR

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Is anyone aware of this CIR being upheld?

12/10/2008 - Credit Interpretation Request

The team is requesting that you please verify the meaning of the
sentence in ASHRAE 90.1, Table G3.1 regarding baseline

envelope requirements for 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". Please confirm if this means that the walls, roof,

windows, etc for the baseline is to be modeled to match the existing
conditions NOT according to the values in Table 5.5-1 thru 5.5-


2/20/2009 - Ruling

If an existing envelope component is untouched, the baseline is as that
component exists. However, if an existing component is

modified, the baseline needs to meet the requirements for alterations in
Section 5.1.3.

It indicates that when modifying the existing envelope, the baseline
needs to meet the minimum requirements of Chapter 5.

Have users in the group received comments from the reviewers when trying
to model modified envelopes at the existing performance values, because
all language regarding this issue other than the CIR indicate that
existing envelopes get to be modeled at existing performance conditions
regardless of any alterations.


Alan Jackson, LEED AP

Jackson, Alan's picture
Joined: 2011-09-30
Reputation: 0

The CIR is wrong and is in direct contradiction to Appendix G and the Energy
Modeling Guide for LEED.

I have never seen a reviewer cite this CIR in a review.

Marcus Sheffer

Marcus Sheffer2's picture
Joined: 2011-10-02
Reputation: 0

>From my understanding, to even apply for LEED you need to meet ASHRAE 90.1-2004/2007 compliance for envelopes, etc?

William Mak

Will Mak's picture
Joined: 2011-09-30
Reputation: 200

So let?s be clear. There is a major difference between code compliance (and
the methodologies for demonstrating it) and applying Appendix G for LEED.
There are also major differences is complying with 90.1 for a new building
versus an existing one.

The envelope provisions in Section 5.5 are not mandatory but are
prescriptive. If you are complying with the code prescriptively then yes
you must comply. As I understand it 90.1 will grant you a prescriptive
waiver for the envelope if a renovation does not affect the system in
question. For example, if you replace windows they must comply for code
compliance purposes; if you don?t replace them the code does not make you do

If applying for LEED certification with an Appendix G model then you must
implement the mandatory provisions and show enough energy savings. Since
the Section 5.5 envelope provisions are prescriptive you do not have to
comply with them. The envelope in an existing building for the baseline
model follows Table G3.1.5(f). The envelope in the proposed model includes
what has been designed and built.

Marcus Sheffer

Marcus Sheffer2's picture
Joined: 2011-10-02
Reputation: 0