Commercial Building Inspector B2Public Safety and Special ConstructionMedium
A building official is reviewing plans for a new six-story mixed-use building (Group R-2 residential over Group B business). The building is fully sprinklered. What is the minimum required fire-resistance rating for the horizontal assembly separating the Group R-2 and Group B occupancies?
- A1-hour fire-resistance rating
- B4-hour fire-resistance rating
- C3-hour fire-resistance rating
- D2-hour fire-resistance rating
Show answer & explanationAnswer & explanation
Correct answer: D. 2-hour fire-resistance rating
According to IBC Table 508.4, the fire-resistance rating for an occupancy separation between Group B and Group R-2 occupancies is 2 hours. This rating is generally not reduced for sprinklered buildings in this specific separation scenario.
Why the other options are wrong
- A. 1-hour is insufficient for this occupancy separation, even with sprinklers.
- B. 4-hour ratings are reserved for very high hazard separations or specific fire walls, which is not applicable here.
- C. 3-hour ratings are typically for more hazardous separations or specific building elements like fire walls, not standard occupancy separation between B and R-2.
Occupancy Separation Rating (B & R-2)
The minimum fire-resistance rating required for fire barriers or horizontal assemblies separating Group B (Business) and Group R-2 (Residential) occupancies.
- Based on IBC Table 508.4.
- Typically 2 hours for B and R-2 separation.
- Purpose is to prevent fire spread between different hazard levels.
- Sprinklers do not always reduce this specific rating.
Memory trick: Different building parts need different fire walls to keep fires apart.