AUST – Hendry reports on a common Building Code of Australia (BCA) compliance design problem encountered on multi storey buildings that arise from design proposals for services risers, including mechanical air handling risers to open directly into a plantroom. To the contrary, compliance with the Deemed-to Satisfy requirements of Clause 2.7 of Specification C1.1 of the Building Code of Australia necessitates 120/120/120 FRL (dependant of Class of building and would not require a structural FRL) lids and fire dampers, or fire rated ductwork to the point of discharge in the case of smoke exhaust systems or the like, unless otherwise justified as an Alternative Solution. The reason for this is that a services riser such as an air-handling riser which opens directly into a plantroom effectively becomes an extension of the shaft, notwithstanding that the plant-room may not be wholly dedicated to being an air-handling plant-room.
As such an alternative solution is warranted for two reasons as follows:
- Although the common interpretation of Clause 3.4(a) of AS/NZS1668.1: 1998 ‘The use of ventilation and air-conditioning in buildings – Fire and smoke control in multi – compartment buildings’, is for fire rated air-handling shafts to open into the highest fire compartment served, the over-riding requirements of Clause 2.7 of Specification C1.1 of the Building Code of Australia, which requires the shafts to be enclosed at the top and bottom by fire rated construction. Deletion of the fire dampers at the top of the shaft is permitted by AS/NZS1668.1 where the shaft is permitted to form a common compartment with the plant room. However, for Clause 2.7 of Specification C1.1 to still be satisfied, the plant room would have to be a dedicated fire rated enclosure, i.e. the fire rated plant room becomes the top of the services risers (shaft).
- The second reason is that the plant room is generally not solely dedicated to being an air-handling plant room whereas the AS/NZS1668.1 provisions are considered to be based on no consideration of other services or uses. The non air-handling plant room uses such as other plant or equipment would not normally be expected to be located in an air-handling plant room which forms a continuation of the shafts.