Structural fire endurance (S) ratings for large single-storey buildings

The Department has become aware that there is a common misperception about where S ratings should be applied for large, unsprinklered single-storey buildings.

The misperception is that there is no need for an S rating if the building is far enough away from boundaries.

The S rating of an element of construction is the fire resistance rating of the element that prevents fire spread or structural collapse in the event of the complete burn out of the firecell.

Paragraph 5.3.2 of the Compliance Document for Fire Safety is quite clear. Sub-paragraph (e) states

S ratings apply to:

(e) Fire separations in firecells which require subdivision due to restrictions on floor areas (see Paragraph 4.2.3).

Paragraph 4.2.3 specifies the maximum floor area of an unsprinklered building for each fire hazard category.

So, for example, a building used for bulk storage of combustible materials (not exceeding 3 metres high) (FHC 3) with a floor area of over 1500 m2 will require an S-rated fire separation whether or not it is close to the boundary.

The Compliance Document requires structural framing members to be fire rated to no less than the rating of the primary or secondary elements to which they are connected. This means floors connected to walls must be fire rated to the S rating as well.