Designed for Life

Estimating the Cost to Build a Duplex


Building a duplex offers a range of benefits that make it a very appealing strategy when it comes to new home builds.

Duplexes allow for multi-generational living, provide an easy way to pay-off a mortgage faster and can also help you dip your toe in the property market water as a landlord.

Most notably, building a duplex is a great way to create equity quickly and is a high growth and high yield investment. The value of land increases significantly with the addition of a duplex, with a large opportunity for return on investment.

That being said, in order to enjoy these benefits, you’ll first have to invest in the development, so how do you estimate how much it’s going to cost you?

Although there is no magic dollar figure we can give you, here are some things you’ll need to consider while you’re crunching those numbers.

Conduct a feasibility study

A feasibility study takes into consideration all of the expenses involved, from buying land to finishing the building, to paying taxes and fees. When measured against the projected yield, this will give you an indicator as to whether the idea is viable.

Some positive indicators you should be looking for are:

  • The site aligns with your planned capital yield
  • The property suits construction zoning restrictions
  • The council regulations in place still allow you to build according to your goals
  • Duplexes sell and rent effectively in the suburb

The below items are what should be considered while conducting a feasibility study:


There are a number of known costs associated with the block of land you choose to build your duplex on. First and foremost, if you do not own the land, you will need to factor in the associated costs of purchase including stamp duty and any relevant council rates.

A thorough site assessment will give you some early insights into how much your project might cost. While we cannot list every single cost, here are some main items associated with the site to consider:

  • Services to site; water, electricity, sewer etc.. While considering this option, you need to consider if you are going to apply for the duplex to be under Torrens Title or Strata (this may be predetermined by local council codes). If Torrens Title, you will be required to have two separate services from the mains to each unit.
  • Hydraulics; which may include onsite detention systems
  • Demolition costs (where applicable)
  • Tree removal or tree protection
  • Retaining walls

It is also important to consider the ‘unknown’ costs that may be hidden:

  • Rock removal,
  • contaminated spoil – this could include buried asbestos, and can even go as far as buried cars, pools and other unusual items.

The ‘unknown’ costs can be quite expensive depending on the severity, so it is always good to have some budget set aside.


Your design,layout and size choices will also have an effect on build cost. Your design will also need to comply with local council regulations and government legislation, including adherence to safety and noise requirements; all duplex (or attached dual occupancy homes) will require a Partiwall System.

You will also need to consider items your local council may require for the design, such as; privacy screens, façade material or façade articulations.

It is important to note, that while all these things do contribute to initial project cost, they will add significantly to the overall value of the property, post-construction.

Development & Construction

Development and construction costs are split over several line items and some will be included by your builder and others will be your responsibility. Again, while we cannot list all costs, here are some important ones to consider;

  • Local council contributions such as S94, bonds and other fees. Note, these can be well over $30,000. We advise you to ring the council your site falls under to enquire what fees may apply.
  • Application costs such as DA’s and CC’s or CDC, plans (including hydraulic plans), any other reports council may require such as Traffic Control Management Plans, Acoustic reports or Arborist reports.
  • Associated costs with subdivision if you decide on a Torrens Title; this includes application fees and additional construction fees (as mentioned above, the services to the site will be affected).
  • Your chosen builder should provide an upfront cost to build your duplex. While they cannot account for some of the ‘unknown’ costs, after completing their due diligence, they should have an accurate price based on these reports to minimise any charges once the construction has started.
  • From start to finish, building a duplex can be a long process, you need to consider your
    holding costs, including interest, council rates, loss of rent etc.

Building a duplex can be very advantageous, while there is a lot of of costs associated, after some careful planning there are a lot of benefits to be realised.

Speak to your builder, and work with them to develop your project estimate by combining their industry knowledge and insights with your design and lifestyle aspirations!

Want to assure yourself that Vogue-Homes should be your builder of choice?

Contact Us to talk to one of our consultants who will be only too happy to answer any questions that you may have.