C/AS2, Paragraph 5.7.10 requires spandrels/aprons when certain conditions are met.
5.7.10 Except where firecells are sprinklered,
unprotected areas in external walls shall be
protected against vertical fire spread if any
of the following conditions occur:
a) An escape height of 4.0 m or more in risk
group SM, or
b) Exitways with an escape height of 4.0 m
or more in risk group CA or 10 m or more
in risk groups WB and VP, or
c) Firecells containing retail areas having an
escape height of 7.0 m or more, or
d) Firecells containing other property
located one above the other.
Lets say a multi-storey apartment building, unsprinklered under single ownership, has first floor with an escape height <4m and remaining floors with an escape height >4m. It is clear that spandrels/aprons are required between the upper floors, but what about between the ground/first floor?
I have seen this interpreted on a firecell-by-firecell basis (i.e. no spandrel at first floor level), or interpreted on a building-wide basis (i.e. if any floor triggers the requirement for spandrels, they are to provided for all floors). Question for the community is which interpretation do you use? Is there a consensus?
With reference to NZBC Clause C3.2 & C3.5 directly, allowing fire spread between the lowest two levels could comply if the storey heights are typical.
C3.2 Buildings with a building height
greater than 10 m where upper floors
contain sleeping uses or other property
must be designed and constructed so that
there is a low probability of external vertical
fire spread to upper floors in the building.
C3.5 Buildings must be designed and
constructed so that fire does not spread
more than 3.5 m vertically from the fire
source over the external cladding of
multi-level buildings.
However, this might invalidate some of the assumptions in C/AS2 (e.g. floors are only exposed to fire from one side at a time). Apparently an acceptable risk for a 2-level building, but what about larger buildings?
Interested to hear your thoughts.