What is the hour rating of the roof in a dry cleaning facility?

• A. Not less than 30 minutes
• B. Not less than 2 hours
• C. Not less than 3 hours
• D. Not less than 1 hour

Answer: (D)

The key idea is fire resistance of the roof assembly. In buildings that handle flammable solvents, like a dry cleaning facility, the roof must be able to resist fire exposure for a certain minimum period to slow the spread of flames and protect the interior long enough for occupants to evacuate and for firefighters to operate. The required minimum in this case is not less than one hour, meaning the roof assembly should maintain its integrity and limit flame passage for at least 60 minutes under standard fire testing conditions. A shorter rating would provide less protection against fire spread, while a longer rating isn’t the basic requirement for this scenario. In practice, you’d verify the one-hour rating on construction documents or with labeling on the roof assembly.