Extensions vs Granny Flats (DPU Accommodation Options)

At their core, home extensions and granny flats are very similar: They are additional structures to an existing dwelling. However, granny flats are primarily built to provide housing for a person dependent on the resident of the existing dwelling. Meanwhile, home extensions can have other functions, like expanding the square footage of a house or converting other spaces into new areas.

For the purposes of our discussion, we’ll consider both of these accommodation options as dependent person units (DPUs). Which is better in terms of features and costs?


Extensions are not relocatable homes. They are permanent additions to existing dwellings. A lot of homeowners add extensions, so they won’t have to leave their current property when they need more bedrooms, bathrooms, or floor space in their home.

Parents whose children are growing up and need their own individual space usually choose this option. Extensions are also typical in remodels such as updating of a kitchen and adding a living area at the back of the house.

An extension is also better if an aged person needs special care (highly dependent). For example, with stroke patients, advanced ages, and other similar cases, the residents of the existing dwelling will be able to easily support them if they all live under the same roof.

In addition, extensions are usually cheaper than granny flats. Space conversions can cost between $5,000 to $50,000 depending on the current state of the space. While story conversions can cost between $1,350 to $3,150 per square metre.                                                                               

Granny Flats

Granny flats are normally relocatable homes, that are located on the same lot as an existing dwelling. They are self-contained structures that have many of the same basic features as a regular home, i.e. granny flats can have a bedroom, a bathroom and a kitchenette.

Homeowners will have to follow local guidelines, if they want to build a granny flat on their property. In some cases, granny flats need to be demolished once the dependent person, doesn’t need it anymore. Therefore, it is not as permanent as a home extension.

Granny flats are great for dependent persons who want to maintain a certain level of independence from the residents of the existing dwelling. Elderly family members who are still active and don’t have special care concerns may want to stay close to the family, but still keep their privacy. Granny flats are also great for young adults who want to be more independent, but are not financially stable enough to leave.

Building a one-bedroom granny flat costs somewhere between $50,000 to $100,000. It is more expensive than a home extension, but you are effectively building another structure on your property.

Which is better?

If privacy is a major concern, then a granny flat is the way to go. There are also granny flat kits that make construction easier, quicker, and cheaper. Otherwise, a home extension is the more affordable option. However, the main house will temporarily be a construction zone if this is the option that you choose. After the work is done though, the extension will be a permanent addition to your home.

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