Overlays explained

An overlay is a map in a council planning scheme showing the location and extent of special features, such as where land may be subject to flooding.

Their key purpose is to:

minimise the effects of overland flows and flooding on new buildings
ensure new developments don’t adversely affect existing properties

Overlays are based on the extent of flooding resulting from a 1 in 100 year storm. This relates to a storm event of such intensity, based on historical rainfall data, which has a one per cent chance of occurring in any given year.

Having this information means drainage issues can be addressed at the start of the development process and proposals are properly designed.

Types of overlay

There are four types of overlay that mean you may need our consent before a planning permission is issued by your council. They are:

Special Building Overlays (SBO)

These are planning scheme controls that identify areas prone to overland flooding. The purpose of these overlays is to set appropriate conditions and floor levels to address any flood risk to developments. These overlays require a planning permit for buildings and works.

Land Subject to Inundation Overlays (LSIO)

These are planning scheme controls that apply to land affected by flooding associated with waterways and open drainage systems. Such areas are commonly known as floodplains. These overlays require a planning permit for buildings and works.

Floodway Overlays (FO)

These apply to land that's identified as carrying active flood flows associated with waterways and open drainage systems. This overlay is categorised by depths in excess of one metre.

Urban Floodway Zone (UFZ)

Unlike the overlays, the UFZ controls land use as well as development, with land use being restricted to low intensity uses such as recreation and agriculture. Development is generally not encouraged in the UFZ.