Enclosure walls depending on building height must have a fire resistance rating of which range?

• A. 3 or 4 hours
• B. 1/2 to 1 hour
• C. 1 or 2 hours
• D. 3/4 to 1-1/2 hours

Answer: (C)

Enclosure walls that protect vertical openings and egress paths are designed with a fire resistance rating that rises with building height. The idea is to keep these barriers intact long enough for occupants to evacuate and for firefighters to respond, even as the potential for vertical fire spread increases in taller structures. For mid‑rise buildings, a rating around one to two hours provides a practical balance: it’s long enough to contain fire for a critical period without imposing unnecessary costs from higher ratings. Ratings that are too low wouldn’t offer sufficient protection in taller buildings, while much higher ratings are typically reserved for taller or more hazardous scenarios. So, the one-to-two hour range best matches the level of protection needed for enclosure walls as building height increases.