The National Construction Code (NCC) series is an initiative of the Council of Australian Governments (COAG) developed to incorporate all on-site construction requirements into a single code. The NCC comprises the Building Code of Australia (BCA), Volume One and Two; and the Plumbing Code of Australia (PCA), as Volume Three.  The NCC is produced and maintained by the ABCB on behalf of the Australian Government and each State and Territory government.  The NCC is Australia’s primary set of technical construction provisions for buildings. It primarily applies to the design and construction of buildings and plumbing and drainage systems in new and existing buildings. In some cases it may also apply to structures associated with buildings and new building work in existing buildings.  The NCC contains requirements to ensure new buildings and structures and, subject to State and Territory legislation, alterations and additions to existing buildings located in flood hazard areas do not collapse during a flood when subjected to flood actions resulting from the defined flood event (DFE).  This Standard provides additional requirements for buildings in flood hazard areas consistent with the objectives of the NCC which primarily aim to protect the lives of occupants of those buildings in events up to and including the DFE. Flood hazard areas are identified by the relevant State/Territory or Local Government authority i.e. the appropriate authority.  Section 2 of this Standard contains basic design requirements for the construction of buildings in flood hazard areas.  Section 2 also contains provisions for the design of buildings in flood hazard areas.  These provisions only apply if certain limits such as maximum flow velocity and depth of submersion, are not exceeded. This does not mean that buildings cannot be constructed if they fall outside these limits if it is permissible under a planning scheme or planning instrument to do so. It means that such a proposal would need to be considered as a Performance Solution under the relevant Performance Requirements and must be assessed accordingly.  The Standard also does not contain provisions that specify particular materials or design solutions which comply with the relevant NCC Performance Requirement. Therefore, in all instances, designers are required to use professional judgment in order to develop designs intended to comply with the NCC Performance Requirement.  It must also be emphasised that the Standard is not a stand-alone solution to mitigating life safety risk due to flooding. Mitigating risk to life in flooding requires a comprehensive set of measures that consider flood hazard and aim to reduce residual flood risk to a manageable level. This set of measures generally involves a combination of effective land use planning considering flood hazard, flood mitigation measures, emergency response strategies for flooding, and building standards. Therefore, with application of this Standard within flood hazard areas, in the absence of supporting measures, it is not possible to guarantee that a building constructed in accordance with the Standard will eliminate the risk of serious injury or fatality even in the DFE.

In addition, larger floods than the DFE can occur and even floods of the scale of the DFE can be unpredictable and could exceed the design parameters and limitations in this Standard. Also, assistance from emergency services or other avenues may not be available to individual properties.

It is important to understand that flood is a local hazard whose parameters, including depth and velocity, vary significantly within the flood hazard area. Modelling of flood hazard generally provides information on average velocities across an area for an event rather than velocities at all points across a location. It is possible to have strong local flow velocities not being shown by such modelling.

In addition, there are significant variations in the information available on flooding between areas within a local authority and between local authorities within Australia. This may result from the age of studies, the type of modelling undertaken, the information available to understand flood behaviour, or the reliance of historical flood information or estimates used to provide an understanding of flood risk. This will mean that the information available is not uniform.

Flood investigations may have also resulted in mitigation works which may alter flood behaviour. These are local by nature and their benefits would generally be considered in studies on flooding for the area and considered by the local authority in determining the flood hazard area.

Existing development in more active flow areas, including floodways, is more likely to be subjected to higher velocities of flow than provided for in the Standard and is also more likely to impact upon flood behaviour elsewhere. Any additional development or redevelopment in these areas is also likely to be exposed to more hazardous conditions and therefore would require careful consideration and assessment. Also note that the flow velocities could also be expected to exceed those specified in this Standard in many areas subject to local overland flooding.

The local authority may need to rely upon its own judgement upon where the Standard applies or request specific information from the proponent. This may limit the application of the Standard by the local authority to backwater and inactive flow areas in the DFE where it is less likely the velocity nominated in the Standard would be exceeded.

In many cases detailed information on the depth of inundation at the development in question will rely upon the provision of survey advice from the proponent relative to flood level information determined in the DFE.

In some cases the local authority may require the proponent to engage a suitably qualified professional to determine the DFE and/or to gain a more detailed understanding of flood behaviour at the location. This may include ascertaining the specific design criteria necessary to enable consideration of the development in relation to the Standard and meeting other requirements established by the local authority.