Resisting fire spread from one building to another

The external envelope of a building should not provide a medium for undue fire spread to
adjacent buildings or be readily ignited by fires in adjacent buildings. This intention can be met by
constructing external walls so that all of the following are satisfied.
a. The risk of ignition by an external source to the outside surface of the building is restricted.
b. The amount of thermal radiation that falls on a neighbouring building from window openings
and other unprotected areas in the building on fire is not enough to start a fire in the other
building.
c. Flame spread over the roof and/or fire penetration from external sources through the roof is
restricted.
The extent to which this is necessary depends on the use of the building and its position in relation
to adjacent buildings and therefore the site boundary.