Planning · Flood
Oct 2025
Brisbane's relationship with flooding is no longer a one-in-a-century concern. The 2011 event was followed by the 2022 event eleven years later. Insurance Council modelling now treats some Brisbane River-bend streets as effectively annual-risk. The City Plan has been updated to match — and if you're building on a Brisbane block, the flood overlay is almost certainly relevant to you, even if your block isn't river-frontage.
FloodWise — your first read of the site
Every Brisbane property has a free FloodWise Property Report, generated on demand. It tells you whether the site is affected by riverine flooding, creek/waterway flooding, overland flow, and storm tide, and what flood planning area the site sits inside. It's free, it's instant, and most buyers never look at it before signing.
FloodWise quotes finished floor levels in AHD (Australian Height Datum). What you want to know:
The Defined Flood Level (DFL) for your site. Typically the 1% Annual Exceedance Probability (AEP) flood plus a freeboard. Your finished floor must be above this for habitable rooms.
The flood planning area designation. Different overlay codes apply to "high", "medium", and "low" hazard categories.
Whether you're in the Overland Flow overlay. Many inner-Brisbane blocks well above river level still flag for overland flow — stormwater concentration paths during heavy rain events. This drives different design responses (raised floors, water-resistant materials on lower walls, robust drainage).
The 2025 mapping update — what changed
The Minor Amendment Package V took effect on 19 September 2025 as City Plan version 34.00. It expanded flood overlay mapping based on updated modelling that incorporated the 2022 event data. The net effect: more properties carry flood flags than did a year earlier, finished floor levels in some flood planning areas have moved up by 100–500 mm, and several streets that were previously "medium hazard" have moved into "high hazard". If you're planning a build on a block you bought before 2025, refresh the FloodWise report — your design constraints may have changed.
QDC MP3.5 — the construction-level rules
The Brisbane City Plan controls whether and where you can build in a flood area. The construction-level rules — what the building is made of below the flood level — come from Queensland Development Code Mandatory Part 3.5 — Construction of Buildings in Flood Hazard Areas. The highlights:
Habitable floor at or above the DFL plus 500 mm freeboard (standard Brisbane practice; some councils require more).
Below-DFL spaces (garages, storage, open undercrofts) constructed of water-resistant materials — fibre cement, concrete, treated steel, certain composites; not plasterboard, not particleboard.
Electrical infrastructure (switchboard, smoke alarm circuit) above DFL.
Hot water systems above DFL or with rapid drain-out provisions.
Designing for flood that isn't theatre
Good flood-resilient design isn't a stilt house. It's a thoughtful interaction with the water you can't fully exclude. Three principles we apply:
Sacrifice the right floor. Treat anything below DFL as garage, storage, deck, or open space — never habitable, never finished as if it is. The 2022 event saw thousands of "rumpus rooms" and "downstairs studios" trashed because they'd been finished out as living space below DFL despite being approved as undercroft.
Plan for the second flood. Material choices and layouts should let an affected house dry and reoccupy within weeks, not months. Removable wet-area linings, accessible underfloor space, drain points at low spots.
Decouple the services. Switchboard, hot water, and any critical equipment above DFL plus generous freeboard. Solar inverter mounted in roof space, not garage.
Insurance and the freeboard question
The 500 mm freeboard above the 1% AEP DFL is the regulatory minimum. Insurance Council of Australia data shows that homes built well above DFL — 1.0 m or more of freeboard — carry materially lower flood premiums and qualify for products from a wider pool of insurers. For sites with deep flood exposure, the case for designing above minimum is increasingly an insurance case as much as a safety case.
The five-year horizon
Three things to expect:
More frequent and more granular flood mapping updates as climate adaptation modelling improves.
Continued pressure on insurance affordability in flood-exposed Brisbane suburbs, with some streets effectively uninsurable at retail premiums.
Probable expansion of mandatory flood compliance disclosure at sale — already on the federal agenda, already partially implemented in some states.
If you're inspecting a block, the FloodWise Property Report should sit alongside the contract. If you're building, the flood overlay should sit alongside the orientation diagram in your concept package. Get the water question right early; everything else gets easier.
If you'd like us to design through a flood overlay constraint on your block, get in touch.
By Ashton Genrich — Building Design — Open, QBCC 15387939