If a building is entirely below grade and has more than 1 storey, what are the FRR requirements for floors?

In the context of buildings that are entirely below grade and have multiple storeys, the Fire Resistance Rating (FRR) requirements for floors are determined based on the occupancy classifications of the building. For Groups E (which typically relates to schools), F1 (high hazard industrial), and F2 (low hazard industrial), a higher level of fire resistance is mandated due to the potential risks associated with these occupancies. Therefore, a 3-hour FRR is necessary to help ensure adequate safety measures are in place for evacuation and fire containment.

Conversely, for buildings that do not fall into these specific occupancy groups, the code permits a lower FRR of 2 hours. This distinction highlights the importance of the intended use of the building when considering fire safety regulations. It acknowledges that certain types of occupancy present greater hazards, necessitating more stringent fire safety measures compared to others.

This approach balances safety with practicality, ensuring that higher-risk categories receive the additional protection they require while still allowing for reasonable standards for less hazardous building types. Thus, the requirement of 3 hours for Groups E, F1, and F2, and 2 hours for all other groups effectively addresses the varying levels of risk presented by different types of building uses.