A practical guide for homeowners in Brisbane, Moreton Bay, Ipswich, Logan and Redland.
Quick Facts – At a Glance
Flood mapping does not automatically prevent a granny flat. The proposed location and level of risk matter.
River, creek, surface-water and coastal flooding need different checks.
The required floor level is specific to the property; it is not a standard height above the lawn.
A raised floor can help, but water flow, structural safety and access still need assessment.
Allow for any survey, specialist report and extra building work before final pricing.
Can you build on a flood affected property
Sometimes. A granny flat may be possible if its location, floor level and construction meet the requirements applying to the site. Higher-risk areas can be unsuitable for additional residential accommodation. Check feasibility before choosing a floorplan or relying on an indicative price.
An overlay is a council map showing a planning issue. It is a starting point for investigation, rather than an approval or a complete assessment of the proposed building.
Understand the type of flooding
River and creek flooding occurs when water leaves its normal channel. Overland flow is rainwater moving across the ground, including through backyards. Storm tide is coastal flooding associated with severe weather and elevated sea levels. A property can be affected by more than one type.
A backyard that has never flooded in your experience can still be mapped for future flood risk. Check current reports, the proposed building footprint and the access route.
What the reports and floor levels mean
Council mapping identifies affected areas. A property flood report may provide levels and development information. A specialist flood assessment examines the particular proposal, including whether the building, fill or fences could worsen flooding elsewhere.
The minimum habitable floor level is the required level for living areas such as bedrooms and the kitchen. Freeboard is an extra safety margin above the relevant flood level. AHD is the common height reference used by surveyors; a level of 10 m AHD does not mean 10 m above your backyard.
A survey may be needed to relate the required level to the actual ground. Where Queensland Development Code MP 3.5 applies, structural design must also address floodwater effects such as flotation and movement. Raising the floor alone does not resolve every requirement.
What to check in all five council areas
For every council, establish the flood type, affected part of the lot, floor-level requirement, safe access, effects on water flow and approval pathway. Do not transfer one council’s freeboard figure to another property.
Brisbane
Start with City Plan mapping and a FloodWise Property Report. Review river, creek, overland-flow and any storm-tide information for the proposed location.
Use the report’s floor-level information where available and ask whether survey or flood-engineering advice is needed. Check planning assessment, access, fill and drainage as well as building approval.
Moreton Bay
Check My Property Look Up, Flood Check Development information, and the separate Flood hazard and Coastal hazard overlays. A coastal requirement may apply alongside ordinary flood controls.
Council’s published flood guidance uses different freeboards in different locations: 300 mm or 500 mm east of the Bruce Highway depending on the erosion-prone area, and 750 mm west of it. These are additions to the relevant flood-event level, not heights above the ground. Confirm the applicable code, access, flow impacts and assessment route for the property.
Ipswich
Use City Plan 2025 and the Flood Risk and Overland Flow mapping and fact sheets. River, creek and surface-water flooding are relevant inland hazards; coastal storm tide is not normally the issue.
Confirm the required floor level, access and effect on water flow. A secondary dwelling can require planning assessment because of a flood overlay even where it meets the usual size allowance.
Logan
Use Logan PD Hub and its linked Flood Portal to obtain current property information. Check the adopted scheme and applicable temporary flood planning instrument; a draft plan is not the adopted rule.
Council’s flood guidance identifies TLPI No. 1/2024 as overriding earlier flood provisions from 6 March 2025. Confirm its current application, floor levels, safe evacuation, fill restrictions and assessment pathway for the proposal.
Redland
Check the Flood and Storm Tide Hazard overlay, property information and applicable City Plan requirements. Coastal and tidal exposure may need assessment as well as creek and surface-water flooding.
Confirm floor levels, safe access, flow effects, earthworks and any planning approval before finalising the design. A neighbouring property’s approved level does not establish yours.
How flooding can change the design
Possible changes include moving the granny flat, using an elevated floor on piers, reducing fill, allowing water to pass beneath the building and raising or protecting services. Extra stairs or a ramp can affect cost and everyday access.
Solid fences and retaining walls can obstruct flow. Ask the engineer to consider associated works as well as the building. Do not fill the site first and investigate the consequences later.
Indicative costs to allow for
All amounts below are in Australian dollars and exclude GST. Add 10% where GST applies. These are preliminary budgeting estimates for this guide, not quotations, fixed Hive charges or council fee schedules. Not every project needs every item, and complex work can exceed the ranges.
Possible cost
Budget estimate excluding GST
What it covers
Specialist flood assessment
A$2,500–A$5,000
A preliminary report allowance; detailed modelling or a difficult site can cost more.
Level survey if required
Obtain a separate quote
Confirm ground and floor levels, boundaries and the exact survey scope.
Raised floors and flood related building work
Builder to price the assessed design
May include piers, structural engineering, stairs or ramp, protected services and drainage.
For example, an A$3,000 report excluding GST is A$3,300 including GST. That does not include a survey, application fees or construction changes. A floor raised 500 mm and a floor raised 2 m can have very different access and structural costs.
Council fees and construction costs are separate. Consultant fees depend mainly on the scope and site, so the same budgeting approach can be used across all five council areas. Obtain a current, itemised quote for the actual property and check what is already included in your design or approval package.
Before you proceed
Confirm the constraint at the proposed building position, identify the reports and approvals actually needed, and have any design changes priced before committing to the final scope. A report supports assessment; it does not guarantee approval.
Request Your Free Site Assessment Report
Start with Hive Small Homes’ Free Site Assessment Report. This preliminary desktop review checks available information for likely setbacks, mapped underground infrastructure and easements, overlays and feasibility issues, subject to verification. It helps identify the next checks before detailed design. It is not a survey, on-site service location, specialist report or formal approval.
Click here to request your Free Site Assessment Report
Hive coordinates feasibility, design, consultants and the approval process. Construction is contracted directly between the homeowner and an independent QBCC-licensed builder.
Related Articles
Understanding Granny Flat Environmental Areas
Understanding Granny Flat Noise Considerations Guide
Understanding Granny Flat Infrastructure and Setback Guidelines
Important Information
This article is general information, not building, planning, energy assessment, engineering or legal advice. Eligibility, floor area, approval pathways, specifications and pricing must be confirmed for each project by the relevant professionals. Published October 2026.
Official Sources
Brisbane FloodWise Property Report
Moreton Bay dwelling houses in flood hazard areas
Ipswich City Plan 2025 overlay fact sheets
Redland development tools and property information
Queensland construction in flood hazard areas
Cost References
Published service examples help establish the order of cost; they are not quotes for a Hive project or identical SEQ services. The ranges in this guide are budgeting estimates. Check the provider’s location, scope and GST treatment when comparing quotations.
