Complete guide to building or renovating a duplex

Doubling the properties on your block? Duplexes are the answer! Use this article as your guide.

Do you own a large piece of land? If so, consider building a duplex on it, then you get two houses for the price of one! 

Duplexes sound like a great deal, right? 

As the price of local real estate properties continue to rise, many Australian property owners are opting to build duplex houses to capitalise on their assets. Doubling the homes on one block boosts its equity and can create an additional stream of income for them.

Whether it’s your first time hearing about duplexes or you are already planning to build your duplex home, continue reading this guide. We will reveal everything that you need to know to successfully build yours, plus we provide all the tools you need to plan and coordinate your project. 

Let’s get started!

Image credit: Domain Australia

What are duplex homes?

Duplexes are residential structures that feature two independent units with a common wall and share a roof. Each unit has its own entrance, utility metres, and amenities (i.e. kitchen, bathroom); the same amenities you’d find in a typical single family home. 

These structures are either on the same or separated land titles. This land title flexibility allows homeowners who own a duplex to: 

  • put up one house or both houses for rent
  • sell one or both houses individually for profit

Here is a perfect example of a duplex home. Scroll to see more photos. 

Popular duplex design and layouts

Duplex homes come in various shapes and configurations. The two dwellings can be joined together either side-by-side or one on top of the other, and can have symmetrical or asymmetrical floor plans, as long as it’s designed to look like a single home. 

In Australia, single storey and double storey side-by-side duplexes are extremely popular because both homes have street appeal. Many homeowners consider up-and-down and front-and-rear duplex designs as well. There’s a solution for every type of block!

Image credit: Greg Brave Photography

Duplex materials and finishes

The units of a duplex can mirror each other inside and out. The two units can have the same interior and exterior material finishes. Duplexes like this are easier to plan and build, and therefore more cost effective. 

Exterior design wise, the best duplexes have uniform colour and material palette, but you are free to give the other house a different facade for distinction. However, it can affect the overall cost.

Duplexes with asymmetrical façades and feature different exterior materials are okay as long as they share the same colour palette and architectural language. Creating too much contrast with the design details is a no-no. Duplex homes should sit harmoniously side by side. The two homes appear larger when they look cohesive. 

Keep in mind that the best duplex home design and layout for you is the one tailored to your requirements, budget, and site conditions. 

Feel free to ask about building your duplex with one of our project consultants here.


Is a duplex right for you?

Duplexes are multi-family units or a type of multi-family real estate, meaning these are for housing multiple families on one block.

Here in Australia, we have noticed a few common duplex ownership scenarios. If you can relate to one or more of these, then building a duplex could be a smart decision for you.

1. You live in one unit, use the other unit to accommodate your extended family

We encounter this living scenario often because many families are looking to build multigenerational homes right now.

As the owner of the duplex, you live in your preferred unit, then invite your family to occupy the other. This living arrangement helps:

  • Established adults take in and look after their ageing parents or a family member who needs extra care
  • Parents can give their young adult children’s independence, but still support them while they save up for a house and their future

You also have an option to build in partnership with another family member. This strategy helps a lot of extended families become homeowners.

duplex real estate
Image credit: Real Estate AU

2. You live in one unit and secure tenants for the other unit

As the owner of the duplex, you live in your preferred unit, then rent the other. 

Many duplex owners across the country use this as a strategy to help them repay their existing loans. They use the tenant’s rent payment to reduce or offset their monthly mortgage payments. 

3. You plan to have a rental property

As owner and a real estate investor, you renovate or build a duplex so you can put all units for long-term rent. This strategy provides you with a steady income, which you can use to pay off debts, fund your next project, or purchase more properties to continue growing your real estate portfolio. 

In some cases, the owner lives debt-free because the tenants’ rent payments are more than enough to cover the mortgage cost. When the loans are paid off, the duplex becomes an income-generating asset.

duplex real estate
Image credit: Real Estate AU

4. You flip houses for a living

Duplexes are positive cash flow properties that deliver immediate returns. These structures can add $150,000+ to the total property value in less than a year after construction.

Able to gain instant equity, selling duplexes for profit is a great real estate business strategy.

The best part? You gain instant equity on both houses! You can sell the houses separately and profit from each one!

If you are planning to flip duplexes, investors highly recommend renovating and building duplexes on good residential locations to maximise the returns.

duplex real estate
Image credit: Real Estate AU

Advantages of building a duplex

By now, you will have begun to see the benefits of building a duplex. You probably have an idea on how to use yours in the future too. 

In addition, here are some more advantages of building and renovating a duplex: 

1. Duplexes offer flexible land title ownership

In Australia, there are two types of title ownership that apply to duplexes. 

The most common and popular is the Torrens titled duplexes. Here, only one person holds the land title and owns the duplex. 

If you are going to build a new duplex, opt for this kind of land title ownership. If you later decide to sell the other unit, you need to change this into a strata title. 

Strata titled duplexes have two owners holding separate land titles. Most strata titled duplexes are joined side by side and have symmetrical floor plans. The owners share home repair and maintenance responsibilities too. 

duplex real estate
Image credit: Real Estate AU

2. Duplexes support multigenerational households

As a multi-family real estate, duplexes enable extended families to live close while maintaining their privacy and independence. There is room for your loved ones who need extra care and more frequent supervision. Children who are old enough to move out can move into their first rental property that’s right next door. This living situation is unique but it can help them save up for their future home.

3. Duplexes can be a stable source of income

Getting tenants for one or both units of your duplex is an excellent way to earn rental income. If you are looking to establish an income-generating real estate investment and your land property meets the requirements to build a duplex, this could be a golden opportunity for you.

duplex real estate
Image credit: Real Estate AU

After knowing all these benefits and advantages, many homeowners realise that it makes a great deal of sense to build a duplex. 

If building a duplex is now a part of your plans, send us a message here and one of our project consultants will answer the questions that you still have. 

Costs considerations for building a duplex home

The budget is the biggest concern of many homeowners when it comes to building a duplex. Here, we answer the questions related to costs of building your duplex.

Is building a duplex more expensive than building a regular home?

Yes, it does it cost more than building one single family home, but its value doubles quickly! A duplex is also cheaper to build when compared to building two freestanding houses on two separate pieces of land. 

As previously mentioned, these cost savings come from maximising one block and building two joined properties on it. With a duplex, you don’t need to buy the neighbouring lot to build a second home. 

Planning wise, building a duplex is still a single project. One building contract is always cheaper than two. 

Image credit: Real Estate AU

Other cost considerations:

  • Design and drafting fees – Keep in mind that the fees of the design and drafting professionals that you will need for a duplex project is different from a single house project, but the overall labour costs and fees are still lower than building two separate homes.
  • Land subdivision fees – Subdividing the land is important especially when you have plans to sell the units separately in the future. Factor the land surveying fees, council fees, legal fees, land title office fees, etc. It is advisable to allocate around $20,000 just for subdivision. 
  • Council and town planning fees – The fees are a bit more expensive than a single family home, but it’s worth it because a duplex gains instant equity right after construction. 
  • Costs of building materials – A duplex is still larger than a single family house. You need more building materials to construct it.
  • Fees of tradespeople – Two homes means you also double the work and pay of your window installers, electricians, plumbers, carpenters, cabinet makers, and more. 
  • Utility and services installation fees – The units of a duplex have separate power, water, gas, and internet services. Double the actual cost of installing these services. 

Knowing all of these cost considerations in advance helps you prepare your budget breakdown in advance and avoid going over budget.

Image credit: Real Estate AU

Site conditions to consider when designing and building a duplex

Apart from the budget, we also need to assess whether your block of land is suitable and not suitable for building duplexes. 

Best site conditions for building a duplex

The following conditions make a site suitable for duplexes:

  • Corner blocks, ideally the ones large enough for the dwellings to have its own driveway and garage.
  • The optimal width of the lot for a standard side-by-side duplex is 18-20 metres. 
  • Slim duplexes can fit on a 15 metre wide block. 
  • The position of the lot allows each unit to face or have as much northern exposure as possible and little from the west (aspect and orientation)

Keep in mind that most local governments have strict and specific requirements for duplex sites. Check if your site is zoned for a duplex. Call your council to check the minimum lot sizes and width requirements. You want to avoid overreaching these coverage restrictions.

If you are going to subdivide the land, your council will set the minimum lot sizes, the size of each dwelling, and number of amenities in each one.

Sites that are not suitable for duplexes

If one or more of these site conditions apply, building another type of residential building might be a better option for you: 

  • Sites under 150 square metres
  • Sites with zero or very limited street frontage
  • Previously subdivided land
  • Wide shallow blocks 
  • Sloping sites from down the road, especially when there are drainage issues
  • Sites where you can’t properly orient duplexes 
  • Sites overshadowed by adjacent buildings

Since the rules and regulations vary per council, it is highly recommended to call and ask them first before moving forward with any work. 

After confirming with your council about the type of project that you can and can do, feel free to send us a message or an inquiry here

One of our project consultants will be in touch with you and provide you with expert advice and guidance as you move forward with your project.

Image credit: Real Estate AU

Common issues and concerns with building a duplex

If you are allowed to build a duplex, decide to move forward with your project and start planning! The design and drafting of the house plans is an integral part of phase. Here, we’ll address the common issues that homeowners have with duplexes. The good news is that we can address them all with proper design!

1. Orientation for daylighting

Here are a few design solutions for this:

  • Backyards must face towards the north so both dwellings will enjoy a healthy amount of daylight. 
  • North-facing windows allow daylight coming into the house. 
  • When possible, install a skylight to illuminate the parts of the house that get dark during the day.
  • Consider a staggered building setback so more light gets into the overshadowed unit.
  • A void in the centre of the dwellings with a massive north-facing window will boost light and will create a greater sense of space. 

2. Noise and privacy

Noise and privacy shouldn’t be a problem anymore because our current building codes have adequately addressed these issues. 

When designing your duplex, choose a designer who knows the local building codes and relevant council restrictions by heart. It will minimise rework, saving you time and money. 

Find a building designer for your duplex project here.

3. Wall sharing getting in the way of getting adequate natural light and ventilation

Side-by-side duplexes often encounter these issues because the firewall splitting them can’t have openings.

Working with a creative architect or building designer can help you avoid these problems. Here are some creative design solutions that you can do:

For double storey side by side duplexes: Not having a party wall on the second level creates physical and visual separation. 

For general side-by-side duplexes: Put the stairs and service rooms on the side of the party walls so the living rooms and bedrooms are beside the outside walls. This design strategy helps you create private, quiet, and well-lit relaxing spaces at home.

Image credit: Real Estate AU

4. Disagreements between unit owners

Disagreements often arise when finalising the style and design, especially when building in partnership with your family. Hold a family meeting and come up with a consensus to avoid more conflict.  

In some cases, the council requires the garages to be in the centre of the house. This design means the unit owners will share a driveway and that is a potential cause of conflict in the future, especially when the units have different owners. 

With proper planning and creative design, you can still give each house separate driveways and still create the central entry that the council requires.

Image credit: Real Estate AU

Process of building a duplex

Building a duplex in general involves three major phases: plan, design, and build.

Within each phase are mini milestones that will help you move your duplex project forward and closer to completion.

Consider signing up for the Dreamspace’s project dashboard to plan and coordinate your duplex project, and to ensure the process runs smoothly!

Sign up for free here.


Professionals you need to design and build a duplex

To build a duplex right, you need the help of the following design and construction professionals: 

  • An architect or building designer to help you with the design and drafting of the house plans of your stylish and low maintenance duplex building designs
  • A land surveyor to conduct property surveys needed, in case you are subdividing the land.
  • A thermal performance assessor to help you design a true energy efficient duplex.
  • A structural engineer to ensure the structural integrity of the building. 
  • And, builders who have experience in duplex home construction. 

Using the Dreamspace project dashboard, you can find these professionals, engage them, and organise their works. With the project dashboard, all these professionals will work together like an oiled machine, helping you finish your project on time and on budget.

Sign up to the Dreamspace project dashboard for free here.

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