What does a one-hour fire rating mean?

A “one-hour” fire rating is given to an assembly consisting of various building materials that can resist the exposure of a standardized fire exposure for one hour. It was developed to evaluate the performance of building elements during an intense fire exposure (for example, fire spreading from one apartment to another apartment sharing a common wall). This kind of rating can be applied to a wall, floor, or roof system. The test follows a standard procedure that specifies the rate at which the furnace temperature is increased over the course of the test (after one hour the furnace temperature is about 1,700°F). The wall, floor, or roof separates the furnace from ambient conditions. A few acceptance criteria for the test stipulate that the fire from the gas-fired furnace cannot penetrate through the assembly during the test. This rating is sometimes used for wildfire applications, but it really doesn’t reflect a wildfire scenario. See FAQ 39221 for more information about construction materials.