Hello everyone,

We have worked on several residential projects, but we want to bring back a question that has some contradicting (and confusing) answers trying to get an updated solid concept about how to select the baseline system for the non-predominant condition when exceptions a and b from G3.1.1 apply.

We are modeling a multifamily building that has 12 stories (1st floor has a lobby, amenities, and retail, and the other 11 floors are residential) and has natural gas-fired boilers for heating; as expected, the main use is residential, therefore system 1, but the issue appears on how to select the baseline system for the other type of spaces (corridors in residential floors, amenities, lobby, and retail) which have about 27,000 sqf (corridors in residential floors have about 22,000 sqf and the other 5,000 sqf are for the amenities, lobby, and retail in the first floor). We have considered two main scenarios to model this building:

Scenario 1:

- System 1 for the residential spaces AND the corridors (predominant condition)

- System 3 for the common spaces on the first floor (under exception a, counting only the area that would be for these spaces, under 25,000 sqf just 1 floor)

- System 3 for retail (under exception b)

Scenario 2:

- System 1 for the residential spaces

- System 7 for the residential corridors and amenities, lobby (non-predominant condition, exception a. Although it is lower than 27,000 sqf, the floor count would be 12, therefore system 7)

- System 3 for retail (under exception b)

The implications (and questions for you) of these 2 scenarios are:

1. Are the corridors in the residential levels considered residential or non-residential?

2. For the non-predominant condition (non-residential) under exception a, should we consider the area and the number of floors? Or only the area?

3. For the non-predominant condition, should we discount the area and/or floors from the 2 different exceptions (a & b)? For example, since the retails are being modeled under system 3, the area and floor for these are not counted for the exception a for the amenities and corridors?

4. What would be the correct scenario here?

So far, although we have been looking for a specific answer to these questions, the answers look like either of these scenarios would be valid, but since this has evolved over the years, we don't know if there is a more up-to-date ruling from GBCI.

Thank you,

P.S.: I’m sending the links for questions related to this topic in the forum.