Shaft enclosures less than 4 stories are fire-rated at __ hours.

Shaft enclosures that are less than 4 stories typically require a fire rating of 1 hour. This is in line with building codes and fire safety standards, which provide minimum requirements for fire resistance in various building components, including shaft enclosures.

The purpose of a fire-rated enclosure is to prevent the spread of smoke and fire for a specified duration, allowing for safe evacuation and minimizing property damage. Since enclosures under 4 stories have less risk associated with them compared to higher structures, a 1-hour fire rating is deemed sufficient to protect occupants and allow for safe escape routes in the event of a fire.

In contrast, higher stories and other critical components might require longer fire ratings due to increased risks associated with greater heights and potential for more significant fire spread. Therefore, the choice indicating a 1-hour rating is appropriate for shaft enclosures of this height.