Vertical separation of openings and spandrel construction - how do they affect your design?

With the increased demand for densification and the current trend for multi storey building design it is worth noting the Building Code of Australia (BCA) requirements for separation of vertical openings in external walls. To minimise the risk of fire spread from one floor to another BCA-2.6 provides deemed to satisfy construction requirements. These requirements apply to residential buildings (apartments and hotels) of 3 storeys of more, other commercial buildings (class 5, 6, 7 & 8) of 4 or more storeys and class 9a (hospital) buildings of 2 or more storeys which are not protected by a fire sprinkler installation.

 The provision of fire sprinklers is deemed to be sufficient to prevent the spread of fire from one floor to another in which case the external wall construction restrictions do not apply. Similarly open- deck carparks are also exempt from the restrictions as it is considered unlikely that fire would spread between floors in these types of buildings as their open construction allows the dissipation of the effects of fire.

 Where vertical separation of openings is required it can be achieved by either of the following methods:

1. A non-combustible spandrel or other non-combustible vertical construction having an overall height of 900 mm or more, extending at least 600 mm or more above the upper surface of the intervening floor, and having an FRL of 60/60/60;

2. A non-combustible horizontal projection (eg balcony) having an outwards projection from the external face of the wall of 1100 mm or more, an extension along the wall beyond the openings of at least 450 mm, and having an FRL of 60/60/60;

With current design trends being to maximise glazing to facades these requirements often prove problematic and require consideration in the design before lodging a planning application as external changes will require re-submission of a planning application.

Design solutions where full height glazing panels are preferred, and sprinklers are not an option, include the use of  balconies as per 2) above or offset of the window openings so their edges are at least 450mm apart so the risk of fire spread from one floor to another is minimised.

Other window opening design considerations that should occur prior to lodging a planning application include BCA Part J2 Energy Efficiency requirements for glazing, and for residential Class 1, 2, 3 & 4 buildings as well as aged care building of class 9c Construction Requirements for the Control of External Sound (Minister’s Specification 78B) and natural light and ventilation requirements including minimum boundary setbacks in accordance with BCA F4.2(b) (in particular greater boundary setbacks are required to ensure adequate natural light to windows as the height of a multi storey building increases).

BuildSurv recommend an early review of concept designs to confirm key compliance requirements are met prior to lodging a planning application. The additional fees involved in undertaking an initial BCA review are minor when compared to the cost savings obtained by avoiding time delays and re-designs that often result when a compliance review is only undertaken later in the design process.