How big can an extension be without planning permission?

Building an extension in Melbourne can be a great way to increase your living space and your home’s value. It’s important to understand the size restrictions so you don’t end up with a kitchen diner that feels unwelcoming or an over-sized bedroom that doesn’t fit well with the rest of your house.

You may have heard that it is possible to build a bigger extension with planning permission but what exactly is the limit?

The answer to this question depends largely on the type of property you have and the amount of extra space you need. If you're extending your house to create a larger living room or kitchen, there are fewer restrictions than for a bedroom extension.

It's best to work out the exact size of your extension before you begin building, so you can be sure it will fit within the available space and that it'll be well proportioned. It's also a good idea to draw up a floor plan for your extension, and to take into account any existing extensions and outbuildings on the plot.

A good way to determine the right size of your extension is to have a chat with your local estate agent, as they can give you an idea of what extended homes in your area are selling for. It's also a good idea for a professional designer to help you with this as they will be able to create the right plans and specifications that will meet your local authority's requirements.

If your new extension is going to sit near your neighbour's house, you need to let them know in advance of building it. This is called the Neighbour Consultation Scheme and it gives your neighbours 21 days to object if they have any valid reasons for doing so.

This is a helpful way to avoid any potential neighbour disputes, but it does mean you'll need to pay a fee to have your project assessed by the planning office and a Lawful Development Certificate (LDC) issued.

Alternatively, you can use a builder to carry out the work for you. They will be able to give you a quote for the project and manage all of the aspects of the construction, including sourcing materials, overseeing work on site, drawing up the plans, and submitting them for building regulations approval.

When it comes to the design and style of your new extension, it's important to ensure it is in keeping with the rest of your home. It should not over-complicate your property, nor should it be over-sized. A good rule of thumb is that the size of your extension should not be more than half the area of your garden.

You should also make sure that the materials used for your extension match those of your original house, as this is the easiest way to avoid any problems. Whether your new extension is built from reclaimed bricks, or using modern materials such as cladding or render, it should be in keeping with the rest of your home's appearance and feel.

Once you've got the design of your new extension sorted out, it's time to get the work underway on the construction site. As with any building project, there are several different routes you can choose to take - from using an architect to hiring a builder or a DIY builder.

Under Permitted Development rules, a single-storey rear extension can be no more than four metres high from the back wall of your original property if it’s a detached house or three metres for any other type.

For a larger single-storey extension (of more than four or three metres), you’ll need to give your neighbours notification under the Neighbour Consultation Scheme, which allows your local planning authority to check that the new building doesn’t impede on their outlook and light.

Rear extensions shouldn’t be built higher than the existing house and can only have a roof pitch that flatters it – think reclaimed bricks or materials that contrast with the building. Exterior material selection should be a key part of your design and planners will look at it closely.

Extension size restrictions vary depending on the area you’re in and the rules can change over time - but it’s always best to have a clear idea of how much space you need before you start work. This helps you avoid wasting money on an expensive project that doesn’t suit your lifestyle or your plot.