Originally published 21 June 2014. Reviewed and updated 7 October 2026. The prices and approval timeframes in the original article have been retired.
Can you build a granny flat on flood-prone land in Sydney?
Flood information needs to be checked for the specific property and proposed building location before choosing a design or committing to a construction budget. A flood flag does not by itself answer whether a granny flat can be approved. Equally, a low-risk description or a neighbouring approval is not a guarantee that your proposal qualifies.
We coordinate your design and approvals and building processes to deliver seamless project completion. For a flood-affected site, that starts with identifying the information and specialist assessments needed for your block.
Start with the property’s flood information
- Obtain the current section 10.7 planning certificate. Read its flood-related information alongside the other planning constraints. It is a starting point, rather than an approval for a particular granny flat.
- Request property-specific flood advice from the council. Ask which maps, flood studies and development controls apply, and whether a flood information report is available for the address. Ask about the proposed building location, access and evacuation, rather than only whether the lot is shaded on a map.
- Provide a survey and a proposed layout. A survey showing levels relative to Australian Height Datum helps the designer and relevant specialists compare ground and proposed floor levels with the council’s information.
- Confirm the approval pathway and reports. Ask the council or certifier to identify the current requirements for the proposal before commissioning the full set of drawings.
Flood mapping and controls can change. Do not rely on a suburb-wide list, an old certificate or the former council boundaries used in the 2014 article. Check the current council information for the actual address.
CDC or development application?
The NSW Housing SEPP provides pathways for secondary dwellings, including complying development where all applicable requirements are met. If a proposal does not qualify for complying development, a development application may be possible. A DA is still an assessment process; approval is not assured.
Flood constraints need to be considered with the other site and development requirements. A certificate describing land as low or medium risk does not automatically establish CDC eligibility. Have the current rules and property evidence checked by the relevant council or certifier.
Read the official NSW secondary dwelling guidance and our Sydney granny flat approval guide for the broader process.
What might the design assessment need to address?
The required assessment depends on the site’s conditions and approval pathway. Discuss the following with the designer, council, certifier and appropriately qualified engineers:
- The location of the granny flat in relation to flood-affected land and overland flow.
- The applicable floor level and how it relates to surveyed ground levels.
- The proposed foundations and any effect on the movement or storage of floodwater.
- Access, isolation and evacuation considerations.
- Any structural, drainage or flood assessment reports needed for the application.
- The relevant consent conditions, inspections and completion documentation.
Raising a floor or obtaining an engineering report does not remove the property’s flood risk. The completed proposal must be assessed against its applicable requirements.
Flood information terms to ask about
- AHD: Australian Height Datum, a reference used when recording survey and flood levels.
- Natural ground level and finished floor level: the existing ground and the proposed finished floor. Their difference alone does not establish flood compliance.
- AEP: annual exceedance probability. A 1% AEP event has a 1% chance of being equalled or exceeded in any year; it is not an event that happens only once every 100 years.
- PMF: probable maximum flood, an estimate of an extreme flood event. It is not interchangeable with a flood planning level or a freeboard allowance.
- Freeboard: an allowance added when determining a specified level. Ask which level and allowance apply to your proposal.
- Overland flow, floodway and flood storage: terms describing how floodwater moves through or occupies land. Ask the council to explain the site’s classification and the implications for the proposed development.
The NSW flood-prone land planning resources explain the planning framework and link to current guidance. Flood considerations can include events beyond 1% AEP and the safety of people accessing or leaving a site.
Approval and building costs on a flood-affected site
The original 2014 fee estimates, foundation allowances and six-to-twelve-week timeframes are no longer presented as current offers. A site-specific scope is needed to establish the reports, design work, council or certification charges and any construction changes.
Use our approval pricing calculator for its calculated approval estimate and our building pricing calculator for its calculated build estimate. Neither calculator is a flood-engineering assessment or a confirmed quote for flood-related works. Ask for a written scope identifying what is included, what remains to be assessed and any additional specialist or authority fees.
Earlier Sydney project examples
The original guide referred to these two projects. They remain useful examples of different sites and building arrangements, rather than proof that another property will obtain the same approval:
- Glenfield project: the 2014 guide described an overland-flow-affected site and elevated piers.
- Panania project: the 2014 guide described a flood-affected site with a raised slab.
Each site needs its own current assessment. View our completed granny flat projects and design catalogue when considering layouts, then check whether the chosen design suits your property’s constraints.
Discuss your property before committing to a design
Send us the address, your current planning certificate, any council flood advice and an existing survey if available. We can discuss the next steps for coordinating the design and approval process. Contact Granny Flat Approvals or call 1300 205 007.
