If a wall has a fire-resistance rating of 4 hours, what should the door assembly be rated?

The door assembly’s fire-resistance rating should generally match or exceed that of the wall in which it is installed to ensure effective containment of fire and maintain the integrity of the fire-resistance-rated wall. In this case, since the wall has a fire-resistance rating of 4 hours, a door assembly rated for 4 hours would logically be the correct answer to accomplish this.

However, in practice, it is often acceptable for door assemblies to be rated lower than the wall they are a part of, provided that the lower rating still meets the necessary codes and safety requirements within the specific context of the building design. Therefore, a door with a 3-hour rating could be considered appropriate under certain circumstances, as it could allow for adequate safety while balancing cost and design considerations.

This understanding explains why a 3-hour rating can be a viable option, even if the recommended rating for the door assembly would be 4 hours. In many scenarios, codes set forth alternatives allowing for slightly lower ratings based on the overall fire protection strategy of the space.