Existing Building, LEED NC

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Good day to all..

Working on modeling an existing building per 90.1 for LEED certification
and can not find clear answers in the standard or users guide- and seeking
of the advise of the Bidg-Sim community-
The building is basically a shell- the 6 inch tilt up concrete walls and
concrete floor are the only things remaining un-changed. The building is
installing new HVAC systems, a new roof, a new lighting systems, new
skylights, new doors, new windows and insulating the existing walls. The
space is 35,000 square feet, and beside another building. The building
owners bought out their former neighbor and are expanding into their space,
the space shares a wall with their current space.

1. Adiabatic wall- Should it be Modeled with an adiabatic wall
separating the "two" buildings (that are actually one building with a
separating wall and separate address), or should the "other building" not
seeking LEED certification be included in the model?
2. Rotated average baseline- This is an existing building and
orientation is set, so is this procedure still necessary or required by
3. Baseline Constructions- Should the baseline reflect the walls as they
where before renovation (Un insulated tilt up concrete walls/R-5 roof
deck?) or should it use the ASHRAE light weight constructions with 2007
insulation for the climate, or should it use the actual constructions but
add ASHRAE 2007 insulation?
4. The HVAC system is a CAV, with convective natural gas heating and and
DX cooling- roof top units, the baseline system for this should be system #
5 PVAV- or should the baseline HVAC system be what ever system was in the
building before the renovation?

An advanced thank you goes out to all that respond-

*Jeremiah D. Crossett*

CleanTech Analytics's picture
Joined: 2012-02-09
Reputation: -1

1. Not sure about this one. although I feel like I read a CIR about it

2. Rotating is not required for an existing building (although I did
rotate a building we put an addition on)

3. Baseline walls are the existing walls.

4. Baseline HVAC is per the table, not the existing HVAC system.

ajuran's picture
Joined: 2011-05-12
Reputation: 0

Thanks- I will check with the Credit interpretation request database for
adiabatic walls, and thanks for the confirmation of my assumptions of the
other questions.

*Jeremiah D. Crossett*

CleanTech Analytics's picture
Joined: 2012-02-09
Reputation: -1


We recently submitted an energy model for the renovation of an existing
building to USGBC (for NC 2009), and although the first round of
comments came back and my model is still not perfect yet, I can answer
what I did to your questions 2, 3 & 4:

2. Did not rotate the baseline and take averages. Only submitted the
baseline for actual orientation.

3. Baseline constructions were existing conditions before the building
was renovated.

4. HVAC system was based on Appendix G of 90.1, not the current/existing
system in the building.

For all the above, USGBC so far has not raised any comments/objections
for my model, so I am hoping I am correct.

Hope this helps.


Ritwik Kakati

Ritwik Kakati's picture
Joined: 2012-07-12
Reputation: 0

Your response is very helpful, thank you much- especially the point about
as built constructions rather then 90.1 light weight/insulation values, or
as built with 90.1 insulation values. (this should get the project some


*Jeremiah D. Crossett*

CleanTech Analytics's picture
Joined: 2012-02-09
Reputation: -1

I agree and suggest you model the common wall (#1) as adiabatic, assuming no services will cross the wall and all the spaces are currently conditioned spaces. If you have an air, water, or refrigerant system serving both sides of the wall, you will have to take the whole system. And if you are converting a semiheated or unconditioned space, use some judgment on the baseline envelope.

As a tangent, we may need to improve the definitions of conditioned space in ASHRAE 90.1. Classifying conditioned/semiheated/unconditioned based on the output capacity of the heating equipment seems problematic, especially for the hyper-insulating & Passive House devotees.

Happy modeling.

Paul Riemer, PE, LEED AP BD+C

Paul Riemer's picture
Joined: 2011-09-30
Reputation: 0

Great points- I do not think that there will be any systems serving both
sides but I will now double check, also will look into the previous space
use and HVAC type to be sure about the baseline envelope

-Thank you for your input.

*Jeremiah D. Crossett*
*CleanTech Analytics*


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