Application of the fire resistance standards in Table B4

The following guidance should be used when applying the fire resistance standards in Table B4.
a. If one element of structure supports or carries or gives stability to another, the fire resistance
of the supporting element should be no less than the minimum period of fire resistance for the
other element (whether that other element is loadbearing or not). In some circumstances, it
may be reasonable to vary this principle, for example:
i. if the supporting structure is in the open air and is not likely to be affected by the fire in
the building
ii. if the supporting structure is in a different compartment, with a fire-separating element
(that has the higher standard of fire resistance) between the supporting and the separated
structure
iii. if a plant room on the roof needs greater fire resistance than the elements of structure
that support it.
b. If an element of structure forms part of more than one building or compartment, that element
should be constructed to the standard of the higher of the relevant provisions.
c. If, due to the slope of the ground, one side of a basement is open at ground level (allowing
smoke to vent and providing access for firefighting) for elements of structure in that storey
it may be appropriate to adopt the standard of fire resistance that applies to above-ground
structures.
d. Although most elements of structure in a single storey building may not need fire resistance,
fire resistance is needed if one of the following applies to the element.
i. It is part of, or supports, an external wall, and there is provision in the guidance on
requirement B4 to limit the extent of openings and other unprotected areas in the wall.
ii. It is part of, or supports, a compartment wall, including a wall that is common to two or
more buildings.
iii. It supports a gallery.