Flood overlay meaning: what it means for your property

A flood overlay means the council has mapped part of the lot as land that floodwater or overland flow can reach, so anything built there has to be designed for the water. It is not a ban on building. It changes what the council asks to see, such as the floor level and where the water goes, and most projects on flood mapped land go ahead once the design answers it.

To check a particular block, type its address into RapidSiteplan: it reads the lot and the rules that apply there and checks the structure you place against them, in minutes.

What do councils typically ask for?

Minimum floor levels: habitable floors set above the mapped flood level
Keep the flow paths clear: sheds, fences and fill must not dam overland flow
Flood-compatible materials below the flood level

What is the difference between river flooding and overland flow?

Riverine mapping follows the waterways. Overland flow mapping follows where stormwater sheets across suburban ground in a heavy downpour, and it regularly maps flat blocks that sit nowhere near a creek. It surprises many people the first time they see their own lot shaded.

How do I check my lot?

RapidSiteplan shades the official flood mapping across your property and warns you when a proposed structure lands in a mapped area, before the design settles. The council's own overlay always has the final word, but you walk in already knowing what it says.

What only your address can answer

whether the lot is mapped, and which part of it
whether the mapping is river flooding, overland flow or both
the flood level the council sets for the lot, and the floor level that follows from it
whether the overlay turns your project into one that needs a planning decision

RapidSiteplan reads your own block from its address: the boundaries, the buildings already on it, the rules that apply there and any overlay or easement, and checks what you plan to build against them on a scaled site plan.

Search your address to start. Site plans and assessments in minutes.

Common questions

What does a flood overlay mean on a property? A flood overlay means the council has mapped part of the lot as land that floodwater or overland flow can reach, so what you build there has to be designed for it. It is not a building ban: it changes what the council asks for, such as floor levels and where the water goes.

My lot is in a flood overlay, can I still build? Usually yes, with conditions. Councils commonly set minimum floor levels, restrict filling, and ask that structures not block overland flow paths. The overlay changes the design, not necessarily the answer.

What is the difference between river flooding and overland flow? River (riverine) flooding is water rising from a waterway; overland flow is stormwater sheeting across land before it reaches the drains. Many councils map both, and overland flow is the one that catches out flat suburban blocks that have never flooded in the river sense.

How do I check if my property is flood mapped? Every state and many councils publish flood mapping. RapidSiteplan shades the official mapping over your lot and warns you when a proposed structure lands in a mapped area. Check the shading before you commit to a layout.