Key takeaways
- On flood-prone land, councils set flood planning levels, and development consents usually require habitable floors to be above them, with a margin.
- The NCC includes requirements for building in flood hazard areas, applied through state and local arrangements, covering structural resistance to flood actions.
- Flood resilience is about recovery as well as avoidance: materials that tolerate water, services above flood level, and details that let a home be cleaned and dried quickly.
- Water-resistant materials include concrete, masonry, ceramic tiles, fibre cement and closed-cell insulation. Plasterboard, particleboard and MDF are among the most vulnerable.
- Electrical switchboards, outlets and appliances should be located above the expected flood level where possible, and sewer backflow prevented.
Flooding causes more damage to Australian homes than any other natural hazard, and the floods of recent years, including the devastating Northern Rivers floods in 2022, have shown how quickly whole communities can be affected. As spring brings the start of the storm season, and as more housing is built in growth areas near rivers and on low-lying land, flood resilience is becoming a core part of residential building.
Planning rules set minimum floor levels on flood-prone land. But floods do not always respect planning levels, and homes that do get wet vary enormously in how quickly they recover. This guide covers the rules, the design approaches, and the materials and services choices that make a home flood-resilient.
The rules
In NSW, councils identify flood-prone land and set flood planning levels, informed by flood studies and the state’s flood risk management framework, set out in the Flood Risk Management Manual gazetted in 2023, which replaced the earlier floodplain development manual. Development consents for homes on flood-prone land typically require habitable floor levels to be at or above the flood planning level, which includes a margin, known as freeboard, above a defined flood level. Consents may also require flood-compatible materials below that level, restrictions on filling land, and consideration of flood evacuation.
The NCC includes requirements for buildings in flood hazard areas, dealing with the structural resistance of buildings to flood actions, such as water pressure, buoyancy and debris impact. How and where those requirements apply depends on state and local arrangements. Builders should read the development consent conditions and the flood-related requirements carefully on any flood-affected site.
Three approaches to flood resilience
Three approaches to flood resilience
| Approach | What it means | Typical measures |
|---|---|---|
| Avoid | Keep water away from the building | Raise floor levels, elevate the house, site the building out of flow paths |
| Resist (dry-proofing) | Stop water entering | Sealing and barriers; suits shallow, short floods only |
| Recover (wet-proofing) | Accept water may enter and design for fast recovery | Water-tolerant materials, elevated services, drainable details |
Avoid
The most effective approach is keeping water away from the building: siting it out of flow paths, raising floor levels above the flood level, or elevating the house on piers or a raised structure. Raised floors with water-tolerant construction beneath, such as a carport, storage or a flood-resilient lower level, are common in flood-prone parts of NSW and Queensland.
Resist
Dry-proofing aims to stop water entering, using sealed construction and removable barriers on doors and vents. It can work for shallow, short-duration floods, but walls and floors can be damaged by water pressure if the water is deep or stays for long, and barriers must be deployed in time. It is a supplement, not a primary strategy, for most homes.
Recover
Wet-proofing accepts that water may enter and designs the building so it can be cleaned, dried and reoccupied quickly, with minimal replacement. This is often the most practical approach for the parts of a building below the flood level, and for homes where raising the whole house is not possible.
Materials
The single biggest factor in how quickly a flooded home recovers is what it is made of below the waterline.
Materials and flooding
| More water-tolerant | Less water-tolerant |
|---|---|
| Concrete and masonry | Plasterboard and paper-faced linings |
| Ceramic and porcelain tiles | Carpet and underlay |
| Fibre cement sheet | Particleboard and MDF joinery |
| Closed-cell insulation | Batt insulation in walls below flood level |
| Stainless or coated metal fixings | Plain steel fixings that corrode |
Source: General guidance; check product manufacturers’ information for flood performance.
Plasterboard absorbs water, loses strength and grows mould, and usually must be removed after a flood. Particleboard and MDF joinery swell and fall apart. Batt insulation holds water in walls and must be removed. By contrast, concrete, masonry, ceramic tiles and fibre cement can usually be cleaned and dried. Closed-cell insulation does not absorb water in the same way.
Practical flood-resilient details include lining the lower part of walls with water-tolerant sheet materials installed horizontally, so they can be removed and replaced in sections; using tiled or polished concrete floors rather than carpet; choosing joinery on legs or made from water-tolerant materials at low level; and using corrosion-resistant fixings.
Services
Services and details that speed recovery
- Switchboard, meters and main outlets above the expected flood level where possible.
- Separate circuits for lower levels so they can be isolated while upper levels stay powered.
- Hot water, air conditioning and other plant raised above flood level.
- Backflow prevention on sewer connections.
- Lower wall linings that can be removed and replaced in sections.
- Joinery on legs or of water-tolerant materials at low level.
- Floor coverings that can be cleaned or easily replaced.
Electrical systems are both a safety hazard and a major recovery cost after a flood. Locating the switchboard, meters and main outlets above the expected flood level where possible, and wiring lower levels on separate circuits that can be isolated, allows faster, safer reconnection. Hot water systems, air conditioning units and other plant should be raised. Sewer backflow prevention reduces the risk of sewage entering the home during a flood.
Floodwater and electricity. After a flood, electrical systems that have been submerged must be inspected and certified by a licensed electrician before being re-energised. Designing services to stay above flood level shortens that process and reduces risk.
Drainage and overland flow
Not all flooding comes from rivers. Overland flow from heavy rain, blocked stormwater systems and poorly graded sites can flood homes that are nowhere near a creek. Good site grading, adequate stormwater drainage, floor levels above surrounding ground, and keeping overland flow paths clear are part of flood resilience on every site. On sloping blocks, cut-and-fill that directs water towards the house is a common and avoidable problem.
Structure and foundations
Floodwater exerts pressure on walls and floors, can make buildings float if they are light and poorly anchored, and carries debris that strikes the structure. Fast-moving water can scour soil from around footings. For homes in flood hazard areas, the engineer considers these flood actions in designing footings, piers, bracing and tie-down, and in anchoring the building against buoyancy. Builders must build exactly to that design; substituting footing details or reducing tie-down on a flood-affected site is not a minor change.
Site works and fill
Filling land to raise a building platform can push floodwater onto neighbouring properties, which is why councils often restrict filling on flood-prone land and may require compensatory measures. Builders should not add fill, raise ground levels or build retaining walls on flood-affected land beyond what the approved plans allow. The same applies to fences and walls that could obstruct flood flows.
Documentation and handover
For owners of homes on flood-prone land, the handover pack should explain the flood-resilient features: which parts of the house are designed to get wet and be cleaned, where the services are and how to isolate them, how the sewer backflow device works, and what they should not change, such as storing valuables below the flood level or replacing water-tolerant linings with ordinary plasterboard in a renovation.
Renovating after a flood
Rebuilding after a flood is an opportunity to build back more resiliently: replacing lower wall linings with water-tolerant materials, raising services, changing floor coverings, and in some cases raising the house. NSW has run programs to help flood-affected homeowners with house raising and resilient retrofits in some areas. Builders working in flood recovery should understand the options and the approvals needed.
A worked example: the house on the floodplain edge
A builder is engaged to build a new home on a lot at the edge of a river floodplain. The development consent requires the habitable floor level to be at the flood planning level, which puts the floor well above natural ground, and requires flood-compatible materials below it.
The design raises the house on a suspended floor, with the area below used for parking and storage. Below the floor, the builder uses masonry piers, concrete, fibre cement and corrosion-resistant fixings, and no storage joinery made from particleboard. The switchboard and hot water system are located on the raised level, and the lower-level lighting and power are on separate circuits. The stormwater design keeps overland flow clear of the house. If a flood above the design level ever reaches the living areas, the home is still designed to be cleaned and dried rather than gutted.
Temporary works and flood risk during construction
A building site on flood-prone land is vulnerable before the house is finished. Open excavations, stockpiled materials, site sheds and temporary power can all be damaged or become hazards in a flood. Check the flood risk for the construction period, keep materials and plant above likely flood levels where possible, secure anything that could float or be carried away, and have a plan for making the site safe if a flood warning is issued. The site emergency plan should cover floods as well as fire and injury.
Climate and future flood risk
Flood studies are based on historical data and modelling, and flood planning levels are reviewed from time to time. Heavier rainfall events and changing development patterns can change flood behaviour. Building above the minimum where it is practical, and using resilient materials even above the flood planning level on higher-risk sites, gives a margin for floods that exceed the design assumptions.
Insurance and resale
Flood insurance availability and cost vary widely by location, and some owners in high-risk areas find cover expensive or hard to get. Resilient construction does not guarantee lower premiums, but it reduces the damage and disruption if a flood occurs, and documented resilient features can be relevant when owners discuss cover with insurers or sell the property.
Talking to clients
Clients building on flood-affected land often focus on the cost of meeting the floor level. It helps to explain the difference between avoiding flooding and recovering from it, and the value of resilient materials and services below the flood level. Insurance is also a factor: flood cover can be expensive or difficult to obtain in some areas, and resilient construction can reduce the damage if a flood occurs.
The bottom line
On flood-prone land, meet the flood planning level and the consent conditions, then go further: choose water-tolerant materials below the flood level, keep services above it, prevent sewer backflow, manage overland flow, and design details that can be cleaned and dried. A flood-resilient home is one where a flood is a bad week, not a rebuild.
Questions builders ask
What is a flood planning level?
A level set by councils on flood-prone land, usually a defined flood level plus a safety margin (freeboard). Development consents typically require habitable floors to be at or above it.
Which building materials cope best with floods?
Concrete, masonry, ceramic and porcelain tiles, fibre cement and closed-cell insulation generally tolerate water better. Plasterboard, particleboard, MDF, carpet and batt insulation are among the most vulnerable.
What is wet-proofing?
Designing parts of a building to tolerate water entering and to be cleaned, dried and reoccupied quickly, using water-tolerant materials and elevated services.
Where should the switchboard go in a flood-prone house?
Above the expected flood level where possible, with lower-level circuits separate so they can be isolated.
Does the NCC cover flooding?
Yes. The NCC includes requirements for buildings in flood hazard areas, dealing with structural resistance to flood actions, applied through state and local arrangements.
Sources
- Construction of buildings in flood hazard areas · Australian Building Codes Board
- Flood risk management manual · NSW Government
Published 31 August 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.
