Commercial Building Inspector B2General Administration, Permits, and PlansMedium
A commercial building inspector is reviewing plans for a new 4-story mixed-use building. The first floor contains mercantile (Group M) and assembly (Group A-2) occupancies, while the upper three floors are residential (Group R-2). All occupancies have separate exits and fire-resistance-rated separations. What is the allowable area of the building primarily based on for this scenario, according to IBC Table 504.4?
- AThe most restrictive occupancy group on the first floor.
- BThe area calculated for each independent fire area, using the tabular area for each occupancy.
- CThe area calculated by applying the highest allowable area factor for the entire building.
- DThe least restrictive occupancy group in the entire building.
Show answer & explanationAnswer & explanation
Correct answer: B. The area calculated for each independent fire area, using the tabular area for each occupancy.
For buildings with mixed occupancies that are separated into different fire areas, the allowable area for each fire area is determined independently based on its specific occupancy group and construction type, as per IBC 508.4.1.
Why the other options are wrong
- A. This applies to non-separated mixed occupancies, not separated ones.
- C. This is incorrect; the highest factor is not applied to the entire building if occupancies are separated.
- D. This is incorrect; the least restrictive does not govern the entire building's area when separated.
Separated Mixed Occupancy Area
In a building with separated mixed occupancies, each occupancy is considered a distinct fire area, and its allowable area is calculated independently based on its specific occupancy group and construction type, as if it were a separate building.
- Each occupancy must be separated by fire-resistance-rated construction.
- Allowable area for each separated fire area is determined using IBC Table 504.4.
- This method allows for larger total building areas than non-separated mixed occupancies.
Memory trick: Separate occupancies are like separate 'Silos' – calculate each 'Silo's' area individually.