Lounging Lizards | Stormwater Plans For Granny Flats
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Stormwater Plans For Granny Flats

Stormwater management plan for granny flats

Stormwater Plans For Granny Flats

Stormwater Plans For Granny Flats In Sydney


According to NSW legislation, all granny flats must have adequate drainage of stormwater for sanitary purposes and to prevent overflow and flooding. The new dwelling will collect water when it rains, and, as such, it must have a system in place that manages the water. This blog will cover your duties as the owner in terms of the plan you must create.

Stormwater management plan for granny flats 

The law states that in order for your granny to be approved, all stormwater “must be conveyed by a gravity-fed or charged system” to:


  • A public drainage system
  • An inter-allotment drainage system
  • An on-site disposal system


In simpler terms, this means that you need to either find a way to naturally drain water away from your property using gravity (usually a downpipe) or aid the drainage either by connecting it to an easement or by installing an on-site dispersion mechanism.


Let us explain:


If your property slopes towards the street


If your property naturally falls toward the street, then you just need to hook your roof drainage up to a downpipe. This pipe will bring water toward the street and take care of everything for you.


What is a drainage easement?


A drainage easement allows the government or utility company the right to use a parcel of land for the specific purpose of draining water. This is normally bad news for the homeowner but it’s great for you! If your property slopes to the rear, you can most likely connect to that drainage easement and drain your stormwater that way.


When you need an on-site disposal system


If you can’t divert your water into a public drainage system or inter-allotment system, your only choice for managing stormwater is an on-site dispersion mechanism. This system will create an artificial means on your property for the dispersion of excess rainwater. These are often called “dispersion pits”.

Dispersion Pit

First, you dig a hole for a good sized prefab pit. The pit itself is a large container with holes punched into the side to allow the gentle seepage of water into the area surrounding it so it doesn’t cause flooding. From there, you fill in the pit with rubble and cover it with grass. This will absorb the water and prevent flooding.


Another option is to dig a trench, but the trench must be located downstream of the granny and 4m long by .6m deep. It must also be 3m clear of structures or boundaries. This often means your flat will have to be constricted to make space for the trench, so be prepared for a squeeze.


In order for your granny to be up to code, it must have a stormwater drainage system. These stormwater plans for grannies are your only options. For the most part, it is relatively simple to drain the water off your property toward the road and prevent flooding. At Lounging Lizards, we rarely have a problem getting approval for your granny regardless of the challenges. Contact us today for your free quote!

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