[Bldg-sim] Appendix G Interpretation: Existing Building Envelope

Jeremy Poling jpoling at epsteinglobal.com
Thu Jun 4 06:59:36 PDT 2009


Nathan,

 

Your conclusion is the same one I have reached in the past in this situation - the existing building clause is the overriding factor.  For existing buildings I interpret that the intent is comparing the proposed model to what would occur if you did not change anything about the existing building.  It does contradict some of the other provisions of Appendix G, but many of those provisions seem designed to develop that arbitrary baseline of what would be considered "minimally compliant" for comparison when a rating authority uses Appendix G.  It gets even fuzzier when you have an addition and renovation together since then you have an existing building baseline for the renovated part of the building and an Appendix G baseline for the addition.

 

Jeremy R. Poling, LEED AP
Senior Sustainability Analyst
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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nathan Miller
Sent: Wednesday, June 03, 2009 7:00 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Appendix G Interpretation: Existing Building Envelope

 

I've run into one of those grey areas of the Appendix G language on a project. We are looking at a major renovation project where the shell of the building will be upgraded. 

 

Clearly the baseline building will be modeled with insulation U-values that correspond to the existing conditions of the building rather than the insulation levels prescribed by tables 5.5-1 to 5.5-8. I think this is pretty well established.


My question is about the quantity of glazing in each case. For this project we will be punching new glazing into the existing façade as part of the renovations. 

 

*         Table G3.1, Section 5 states that "Vertical fenestration areas for new buildings and alterations shall equal that in the proposed design or 40% of gross above-grade wall area, whichever is smaller." So if we add new windows, it would seem that the baseline building should also have those windows, but what should their U-value be? Same U-value as the other existing windows? Lookup the value for new glazing?

*         Lower in that same section of Table G3.1 it states: "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." To me, this seems to say that you would go with the existing quantity of glazing, and the proposed model would have more glazing than the baseline, even if the proposed does not exceed the 40% cap.

 

There seems to be a little contradiction between the two requirements. My inclination is that the existing building clause overrides the requirement that the same amount of glazing be used in each model. 

 

Have any of you worked on a project where this came up? Any thoughts? It seems like this could potentially be one of those hot topics of discussion. 

 

Thanks,

 

Nathan Miller, PE, LEED® AP

Senior Energy Engineer/Mechanical Engineer

direct: 206.788.4577

fax: 206.285.7111 

www.rushingco.com <http://www.rushingco.com/> 

 

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