What is a duplex and should you build one?

modern duplex house in Melbourne


Posted August 23, 2023

Thanks to the duplex residential building, it is possible to build two homes for the price of one on a block of land.
So, you’ve got your block of land, and now, you’re trying to decide how best to maximise the space. Have you considered a duplex? That way you’re getting two houses, essentially for the price of one.

What is a duplex?

A duplex is a residential building containing two homes that share a common wall but sits on separate titles. So, a duplex looks like one house, shares the same roof, and are mirror images of one another.  

Because there’s two separate entranceways, the style of build provides homeowners with dual occupancy listed on your title, providing income opportunities as a landlord, or the chance to have family or children next door. Best of all, they can be cheaper to build. 

Essentially, building a duplex allows you to divide one piece of land into two. And you can subdivide, meaning you’ve got two separate properties on the one block.  

This means that a duplex can help homeowners unlock hidden equity in their property by changing their single occupancy into a dual occupancy.  

Daniel Peterson heads up property investment firm, iBuildNew. He says the duplex design appeals to downsizers and investors mostly, but that if you’ve got a block of land, it’s definitely worth contemplating if it might work. 

Bear in mind, building a duplex is not a DIY type of project. You’re going to need to call in the experts.  
“A dual occupancy could work well for some homeowners, landowners and prospective home buyers and renters, depending on their situation,” Peterson says.

modern duplex house in Australia

A duplex is two homes that share a common wall, but sit on different titles. Image: Getty


What are the benefits of a duplex? 

The benefits are endless. For starters, a duplex approach enables the home buyer to contemplate purchasing in exclusive neighbourhoods and build at a lower price - a real alternative to downsizing to an apartment.

A duplex can also be a great approach given that adult children are struggling to get into the Australian property market. This means multi-generational families can essentially live under the one roof, while also having privacy. 

Peterson adds: “There can be real merit to building a duplex. Sometimes the person building the duplex will live in one side, and sell the other side, or invite their adult children to live in the other home next door. If they’ve got young children, that means they’ve got babysitters under the same roof, which can be handy,” Peterson says.

What should I consider when designing a duplex? 

When designing the layout of a duplex, it’s important to consider the configuration of each property, including elements such as privacy, window placement, configuration and natural light. 

Depending on local regulations, duplexes are usually double storey, but even three-storeyed designs can receive approval, depending on your suburb.

If you’re investing, the good news is that a duplex can produce strong growth and healthy rental yields for less than the cost of two similarly located detached homes.  

Peterson says: “It’s very important to look at what the market wants in that area, and be very clear about the market and whether it’s the right investment for you.”

How much does building a duplex cost?

As a guide, the cost to build a three to four bedroom duplex in Melbourne is around $350,000 to $450,000 each, so around $700,000 to $900,000 altogether, depending on the location, size and finish, Peterson says.

How much land do you need for a duplex home? 

Whether or not you can build a duplex will come down to the size of the block that you’ve purchased. “You need a wide block of land to be able to fit a duplex, and you will need to give careful consideration to the layout of each property to see if it will work on the block,” Peterson says.

While large blocks in Melbourne's middle and outer suburbs are well suited to side-by-side duplex development, many homes in inner-city Melbourne don’t have the width to allow for a duplex. However, it is possible to build a duplex one behind the other, with the driveway on one side. The downside of this is that the back home doesn’t have street appeal, which counts for something when considering resale.

Can you sell half or both parts of a duplex?

That depends on whether your duplex is strata titled or not. If strata titled, you can sell and own one dwelling in the duplex. If non-strata titled, you must sell or own both dwellings in the duplex.

Do duplexes have strata fees?

If your duplex is strata titled, you will have to pay strata fees. If your duplex is non-strata titled, you are exempt from strata fees.

Can you turn a duplex into a single home?

You can generally convert a duplex into a single-occupancy home, but you may be better off selling your duplex and purchasing a house. Turning a duplex into a single home is a lot of work, from consulting your local authorities about what kind of permits you will need to demolishing the separating wall to coming up with a new floorplan for the house.

Are duplexes soundproof?

In general, there is more risk of sound transfer in a duplex than in, for example, two neighbouring houses. In the construction stage, ensuring that additional soundproofing measures like double-glazed windows and insulation are added will help prevent sound transfer.


man and woman moving into a new home

When designing a duplex, it is important to consider privacy, window placement, configuration and natural light. Image: Getty


What’s the catch with a duplex? 

Whether or not a duplex will work for you depends on your personal situation. Duplexes are sometimes on one title, meaning both halves must be sold together. If a duplex is subdivided into two separate titles, each home can be sold separately, says Peterson. 

The other obvious downside is that if you end up with bad neighbours who constantly play loud music, which you’re probably going to hear that through the shared wall, which could impact on your quality of life. 

There can also be additional costs to build a duplex, so don’t get caught out.  

These extra costs can include tax costs, civil engineering costs and the connection of services, levies and taxes, he says. So, make sure you crunch the numbers first. 
Also, be sure you contact the relevant authority for more details. 

“The advice here is to make sure you speak to a residential home building expert and weigh up the decision to construct a duplex. While duplexes are a great opportunity for many, they may not work for everyone,” Peterson says.


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