• Why not?

Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

• I thought we don’t include storage and restrooms in the net square footage. Only in gross ?

• Building efficiency is most commonly expressed as a percentage calculated by dividing the usable floor area by the gross floor area. Restroom and storage are part of the usable floor area and should be included.

Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

• okay, thank you for clarifying. So what would not be included when calculating the building efficiency?

Stairs, elevator shaft, ...?

• According to what I've studied, when talking about building efficiency there are 2 different definitions: Overall & Basic

Overall building efficiency= Net floor area/ Gross building area (O=N/G)   <the Net Floor Area here means the Main Task area, for office building, office units are the main task areas. Everything else should be excluded, eg. corridor, lobby, public bathroom, mech room, stair, elevator, shaft...>

Basic building efficiency= Usable floor area/ Gross building area (B= U/G)  <the Usable floor area here means the Net floor area + circulation area (corridor, hallway, lobby..) >

* There is another formula came from the above, Interior layout efficiency=Net floor area/ Usable floor area (I=N/U)

Your confusion of "Net Floor Area" definition may caused by you are unclear about which standard is using in ARE test, see the explanation below. In ARE test, the standard should be the ANSI/BOMA.

• yes, this is truly confusing, and in my opinion NCARB should definitely clarify that for the test.

Thank you for the explanation and resource.