This guide is for Brisbane homeowners planning to raise a house, extend, build in underneath or knock down and rebuild. Whether you’re in Wynnum near the bay, Chermside near Kedron Brook or a hillside street in Indooroopilly, look up your flood information before anyone draws a line. Flood levels set the minimum height of your habitable floors, and that height shapes the whole design.
The good news is that Brisbane City Council publishes this information for free, property by property.
Four kinds of flooding, not one
Council’s flood information covers four sources of flooding in Brisbane:
- River flooding from the Brisbane River
- Creek or waterway flooding from local creeks
- Storm tide flooding near the coast and river mouth
- Overland flow, which is rainwater running across the land during heavy storms.
A property can be affected by one or several. Overland flow is the one people miss. You can be kilometres from a creek and still sit in a path where stormwater runs across the ground. Council describes overland flow as unpredictable, often arriving very quickly and lasting a short time.
Flood Awareness Map vs FloodWise Property Report
Council offers two tools through its Flood Information Online hub. They do different jobs.
| Tool | What it’s for | What it won’t tell you |
|---|---|---|
| Flood Awareness Map | A quick, general view of the likelihood of river, creek and storm tide flooding, and the impact of overland flow, on a property | Flood depth or speed, or the levels you must build to |
| FloodWise Property Report | A technical report with ground levels, flood levels, the minimum habitable floor level (where available), flood planning areas and development flags | A minimum habitable floor level for large lots or properties in an overland flow path |
What the likelihood categories mean
The Flood Awareness Map uses these categories for river, creek and storm tide flooding:
| Category | Chance in any year |
|---|---|
| High likelihood | 5% (1 in 20) |
| Medium likelihood | 1% (1 in 100) |
| Low likelihood | 0.2% (1 in 500) |
| Very low likelihood | 0.05% (1 in 2,000) |
For overland flow, Council uses impact areas instead: high impact (5% chance in any year), medium impact (2%) and low impact (1%).
A “1 in 100” flood doesn’t mean once a century. It means a 1% chance every single year.
How to get your FloodWise Property Report
- Go to Council’s Flood Information Online and open the Flood Awareness Map.
- Type your address, lot and plan, or suburb into the search bar. Your property is outlined in red.
- Read the Flooding Overview panel for a summary of flood types and likelihoods.
- Click “Technical FloodWise Property Report”. Council says it takes about 20 seconds to generate.
- Check the header shows the right address and lot. Save the PDF and send it to your designer, surveyor and certifier.
Reading the report
The report is written for surveyors, builders, certifiers, architects and engineers, but you can follow the key parts.
- Ground levels. The minimum and maximum ground level on the property, in metres AHD (Australian Height Datum, where 0.0 m is mean sea level).
- Indicative existing floor level. The approximate level of the lowest habitable floor in the current house, where recorded.
- Flood levels. Levels for river, creek and storm tide at 20%, 5%, 2%, 1% and 0.2% annual likelihood, where they apply.
- Historic floods. January 2011 and February 2022 levels, where available.
- Minimum habitable floor level. For a dwelling house, this equals the 1% AEP flood level of the highest flood type plus 0.5 metres. It’s the minimum level City Plan requires for habitable areas.
- Flood planning areas and overlays. Whether City Plan’s flood overlay applies for river, creek, overland flow or coastal hazard.
- Property development flags. For example an overland flow path, a waterway corridor, or a large allotment flag (over 1,000 square metres).
A simple worked example
These numbers are made up for illustration. Say your report shows a 1% AEP creek level of 10.0 m AHD and your ground sits at 8.8 m AHD. Your minimum habitable floor level is 10.0 + 0.5 = 10.5 m AHD. That’s 1.7 metres above the ground, before you allow for floor framing. Anything you want to use as a bedroom, living area or kitchen has to sit at or above that line.
Overland flow is handled differently
Here’s the catch. Council has flood levels for river and creek flooding in the FloodWise report, but it doesn’t publish overland flow flood levels. If your property is in an overland flow path or is a large lot, the report may not show a minimum habitable floor level at all.
In that case Council recommends engaging a Registered Professional Engineer of Queensland (RPEQ) to work out the level for your site. Council’s fact sheet on raising and rebuilding gives its current standard for minimum habitable floor level as the higher of:
- the Residential Flood Level for the Brisbane River plus 500 mm
- the 1% AEP creek or waterway flood level plus 500 mm
- the 2% AEP overland flow flood level plus 500 mm.
Overland flow also affects where you can put things. A new extension, a built-in lower level or a solid fence across a flow path can change how water moves, so expect your designer and engineer to look at this closely.
Download the FloodWise Property Report the same day you look up your City Plan overlays. Hand both to your designer at the first meeting so the floor levels are right from the very first sketch.
How flood levels change your project
Raising
Raising is often the obvious way to get above flood levels. In general a house over 9.5 metres high (measured to the top of the roof) needs a development application. Council says it will consider applications to raise houses above 9.5 metres to achieve flood immunity. If your block is also in a character overlay, those rules apply too.
Building in underneath
Council treats bedrooms, living rooms, kitchens, studies, family rooms and rumpus rooms as habitable areas. If the ground floor would sit below the minimum habitable floor level, you may not be able to use it for those rooms. Ask your designer and certifier early what’s allowed on that level for your site, rather than designing a downstairs living area and finding out later.
Extensions
A new extension generally needs to meet current flood rules, even if the existing house doesn’t. Matching your old floor level may not be enough.
Approvals
Whether a house needs planning approval depends partly on whether it meets the acceptable outcomes of City Plan’s Flood overlay code. If it doesn’t, expect a development application on top of your building approval.
What drives the extra cost
Flood-affected sites don’t come with a set price, but these are the things that add to it:
- a survey to confirm ground and floor levels
- an RPEQ flood assessment, especially for overland flow
- extra height, which means longer stairs, more structure and more engineering
- flood-resilient materials and services placed above flood levels
- planning approval, if the design doesn’t meet the flood code.
Council points out that minimum habitable floor levels are not full flood immunity. They’re a construction standard. Building higher than the minimum gives you more protection.
If you think the levels are wrong
You can ask Council to review the levels in your FloodWise report. Council asks for supporting evidence such as certified survey levels, as-constructed plans, or hydraulic assessments or flood studies certified by an RPEQ. Requests go to FloodPropertyReport@brisbane.qld.gov.au or the Flood Information Officer by post.
Checklist before you pay for drawings
- Check the Flood Awareness Map for your address.
- Download the Technical FloodWise Property Report.
- Note the minimum habitable floor level, or note that it’s missing.
- Look for an overland flow path or large allotment flag.
- Get a survey with ground and existing floor levels in m AHD.
- If overland flow applies, talk to an RPEQ before design.
- Check your City Plan overlays and any height limits.
- Give all of this to your designer as part of the brief.
Questions to ask your designer or builder
- What’s our minimum habitable floor level, and where did that number come from?
- Does overland flow affect the site, and do we need an engineer’s assessment?
- Will the new height trigger a development application?
- What can we legally use the lower level for?
- Have you allowed for flood-resilient materials and raised services?
Who to talk to
Through the Build in Brisbane directory you can find:
- Surveyors for certified ground and floor levels
- Engineers (RPEQ) for flood and overland flow assessments
- Town planners if the flood overlay or height triggers a development application
- Building designers and drafting services to design to the right levels
- Building certifiers for building approval
- Builders and house raising specialists who’ve worked on flood-affected sites.
Sources
- Brisbane City Council: FloodWise Property Report
- Brisbane City Council: Understanding flood likelihood and impact
- Brisbane City Council: Flood information frequently asked questions
- Brisbane City Council: Flood-resilient design and building requirements
- Brisbane City Council: Severe weather fact sheet, Repairing or rebuilding dwelling houses (PDF)
- Brisbane City Council: Flood technical review process and level updates
- Brisbane City Council submission to the Queensland Floods Commission of Inquiry (definition of habitable areas, PDF)
This guide is general information only, not legal, engineering or planning advice. Flood mapping and City Plan are updated from time to time. Confirm the current requirements for your property with Brisbane City Council, a certifier or an RPEQ before you design or build.