Floodproofing And Granny Flats - What You Need To Know

July 5, 2022

Flood damage to your property can be utterly devastating, and if you’re planning on building a Granny Flat, it’s crucial to take strategic measures to minimise your flood risk. Find out everything you need to know and what measures you can take to minimise your risk of flood damage and ensure your Granny Flat meets flood safety requirements.

How can I tell if my property is flood prone?

If you’re building a Granny Flat on your existing property you probably have some idea of your land’s flooding risk – however, it’s vital to seek a professional assessment of flood risk prior to beginning construction of your flat. To determine if your property is flood-prone, you can take the following steps.

Water leaking and flooded on wood parquet floor. Room floor will damage after the water flooded.

1. Request a section 10.7 (2) certificate and 10.7 (5) from your Local Council.
A section 10.7(2) and 10.7(5) certificate provides information on property zoning, relevant planning controls and any property constraints such as bushfire risk, land contamination and flooding risk.

2. Obtain local flood information.
If the section 10.7 (2) and 10.7(5) certificate shows your property is flood-prone, you’ll need to request flood information from your Local Council, if available, to gain a clearer picture of your property’s flood risk. This information can provide details on what type of flooding the area is prone to and the depth of floodwaters.

3. Obtain planning help from a Civil Engineer.
If your property is flood-prone, the information you’ve gathered from Council can be used by a Civil Engineer to provide advice on what flood measures need to be taken to protect your property.

What are the three most common forms of flooding?

There are three common types of flooding which can impact properties:

  1. Slow onset flooding from inland rivers.
    This form of flooding may last for weeks or even months and can result in flood islands, or areas of land which are cut off by flood waters.
  2. Rapid onset flooding from mountain rivers and coastal rivers.
    This form of flood may last one or two days. Rapid onset flooding has a faster velocity and can pose a greater risk to life and property.
  3. Flash flooding from intense rainfall.
    This form of flooding can occur almost anywhere in Australia and is worst in areas with poor drainage systems. This form of flood poses the most significant risk to life and property.
Infographic - Types of flooding

What flooding-related documents are required when building a Granny Flat?

There are a range of important approvals you need to obtain before building a Granny Flat – or any building – including approvals associated with flood risk. General flood documents required for building approval include the following items.

Full length of construction workers analyzing blueprints in the apartment while one of them is aiming at distance.

Flood Compliance Certificate

This document supports the complying development application to confirm the proposal meets all relevant flood-related requirements for a complying development approval.

Flood Risk Management Plan

This document supports a development application, or complying development application, to confirm there are adequate measures in place to ensure safe evacuation from the property in case of a flood.


This document is required when your property is categorised as flood-prone and your Local Council do not have sufficient information on record to determine the effects of previous and/or future flood events.

Can I still build a Granny Flat if I live in a flood-prone area?

In most cases, yes you will still be able to build a Granny Flat on your land even if it is a flood risk. However, you will need to engage the services of a Civil Engineer and obtain proper documentation to ensure all precautions are taken to minimise your risk of property damage.

How will floodproofing impact the cost of my Granny Flat project?

Assessing your flood risk is a compulsory part of any building project, however, if extra measures are needed to floodproof your property it can impact the cost of your Granny Flat build. The cost of floodproofing your Granny Flat will vary depending on the complexity of your needs and the number of professionals involved. Some common floodproofing factors which can increase the cost of a Granny Flat building project include the following services.

Stormwater management

This is the management of the amount and quality of stormwater that is allowed to flow onto your land.


If the services of a Civil Engineer are required this will inevitably drive up the cost of your building project.

Raised home design

Raising your Granny Flat on stilts of pillars can help reduce the risk of flooding but will require extra materials, planning and labour which will carry additional costs.


If you’re building a Granny Flat in a flood-prone area the cost of insuring your property will be higher than that of one built outside of a high-risk flood area.

At the end of the day, taking steps to minimise the risk of flood damage to your Granny Flat prior to construction will cost far less than having to start over after losing your flat to flooding.


Talk to Cubitt's about building a flood-proof Granny-Flat

With an experienced in-house council planning and drafting team who take care of the approval process, you can rely on the Cubitt’s team to accompany you during the entire process. We offer a comprehensive, full-service Granny Flat building process which includes all floodproofing and certifications. Don’t leave anything to chance, with Cubitt’s you can ensure your Granny Flat is built in the best possible location and is as protected as it can be from natural flooding.

Plus, we offer free feasibility studies during which we can determine if your property is flood-prone and advise the best path to approval for you. Our fully transparent, upfront quote will cover all floodproofing costs. Call us on
1300 721 150 or email us at hello@cubitts.com.au to arrange your free consultation and quote.

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About Harry Kim

Harry has worked on building sites since the young age of 16, both on commercial and multi high rise buildings, before moving into residential construction management with Cubitt’s. Harry leads a team of 10 site supervisors, 30 employee trades and a large, fluctuating group of longstanding subcontractors.