Occupancy

Occupancy is a defined legal term in building construction and building codes. It refers to the use or intended use of a building or part thereof for the shelter or support of persons, animals or property. A closely-related meaning is the number of units in such a building that are rented or leased, or otherwise in-use. The lack of occupancy in this sense is a vacancy.

Building code

It is possible to have multiple occupancies (or building uses) within one building. For instance, one may have a high-rise building, where the lower levels are occupied by retail stores, whereas the upper levels could be residential.

Different occupancies within one building are separated by a fire barrier^[1] with a defined fire-resistance rating. It is common for a penetration, such as a fire door, to have a fire protection rating lower than the wall fire resistance rating in which it is installed^[2]. For example, a two-hour fire separation normally requires fire doors rated at 90-minutes.

For some high challenge occupancies^[3] the code requirements for an occupancy separation are more stringent than for other fire-barriers, even with an identical fire-resistance rating. In this case, an occupancy separation with a two-hour fire-resistance rating may not be able to de-rate its closures, such fire doors or firestops. For example, a two-hour rated high challenge fire wall^[4] requires 2 hr rated fire doors.

Firestops in occupancy separations are also more likely to be required not only an equal fire protection rating (a fire-resistance rating for closures) but must also provide a temperature rating, such that the components of the firestop systems, including the penetrants, are not permitted to rise in temperature above 140°C (284°F) on average or 180°C (356°F) on any single point, so as to lower the likelihood of auto-ignition on the unexposed side. In this manner, occupancy separations are treated similarly to fire walls, which are structurally stable in case of a fire, limiting fire-induced building collapse.

In this sense, there are two occupancies in most single-family homes: the garage and the living space of the home. Because automobile gasoline or petrol is flammable, an occupancy separation is often required between the two, should there be a vehicle fire. Water heaters and central heating are often placed in this space as well, for their use of natural gas, propane, or other fossil fuels in combustion. This also helps to prevent carbon monoxide poisoning.