When Two is Better Than One: Duplex Questions Answered
Downsizing, multi-generational living, investment – there are many reasons to consider a duplex. Is it right for you?
Georgia Madden
15 July 2020
Two houses for the price of one – sounds almost too good to be true, doesn’t it? Building a duplex creates the potential for considerable profits, but will it be as much as you think and what are the downsides (if any) in terms of the homes’ liveability and looks? We spoke to three architects to find out.
A duplex is typically two buildings that are joined together, either side-by-side or one on top of the other, says David Homer, project leader at Archisoul Architects.
“Typically these buildings are cleanly divided by a single wall or floor, however with more complex floor plans the two buildings can be more intricately connected, sharing several walls and sometimes courtyard spaces too,” he says.
A duplex can be built to other configurations as well, including two freestanding homes or one in front of the other, says Peter Couvaras, principal architect at Couvaras Architects. “And they don’t have to be symmetrical or mirror each other – one dwelling can be bigger, the layouts can be different and the building can be designed to look like a single dwelling.”
“Typically these buildings are cleanly divided by a single wall or floor, however with more complex floor plans the two buildings can be more intricately connected, sharing several walls and sometimes courtyard spaces too,” he says.
A duplex can be built to other configurations as well, including two freestanding homes or one in front of the other, says Peter Couvaras, principal architect at Couvaras Architects. “And they don’t have to be symmetrical or mirror each other – one dwelling can be bigger, the layouts can be different and the building can be designed to look like a single dwelling.”
What are the main advantages of building a duplex?
Homer says:
Homer says:
- You can offset some of the building costs against the sale price of the second dwelling, making developing a dream home a far more achievable goal.
- Two families could purchase one lot and split the development costs, again making their dream more reachable.
- You could potentially rent the second dwelling to generate passive income.
Do they have to be designed as a mirror image?
Not necessarily – particularly if you have a corner site, says Jolyon Robinson, principal at Robinson Architects. “But the buildings should still share the same architectural language – to not do so would be a mistake.
“One device we have employed is not having a party wall on the second level. This creates some physical and visual separation. The occupants feel they are in totally seperate homes.
“You can make one a two-bedroom and the other a three-bedroom home or you can create voids between the two levels to create a greater sense of space,” he says.
Not necessarily – particularly if you have a corner site, says Jolyon Robinson, principal at Robinson Architects. “But the buildings should still share the same architectural language – to not do so would be a mistake.
“One device we have employed is not having a party wall on the second level. This creates some physical and visual separation. The occupants feel they are in totally seperate homes.
“You can make one a two-bedroom and the other a three-bedroom home or you can create voids between the two levels to create a greater sense of space,” he says.
Render of a duplex by Russell Rice at Archisoul Architects
Does it cost more than building one home?
“Yes, but a duplex can have almost double the value of a single home,” says Homer. “A duplex is much cheaper than building two single homes and each duplex will be of a similar value to a single home.
“The advantage comes from the ability to purchase once piece of land and gain two homes,” he says. “One building contract will be cheaper than two, and professional fees for architects, engineers, surveyors and town planners will be more similar to a single dwelling. The fact that the work for two dwellings will occur simultaneously reduces labour cost and set-up fees.”
Does it cost more than building one home?
“Yes, but a duplex can have almost double the value of a single home,” says Homer. “A duplex is much cheaper than building two single homes and each duplex will be of a similar value to a single home.
“The advantage comes from the ability to purchase once piece of land and gain two homes,” he says. “One building contract will be cheaper than two, and professional fees for architects, engineers, surveyors and town planners will be more similar to a single dwelling. The fact that the work for two dwellings will occur simultaneously reduces labour cost and set-up fees.”
“Subdivision costs are often not factored into the build cost, and can be a surprise at the end,” says Couvaras. “Subdivision is the legal process of dividing the land into two houses that can be sold independently of each other (either Strata title or Torrens title).
“There are costs associated with this process, such as surveyor fees, legal fees, council fees and Land Titles Office fees. The whole process can add between $15,000 and $20,000 of unexpected costs right at the end of the project – often when money has run out,” says Couvaras.
“The process can take six to eight weeks if you are not well organised. Holding costs on the dwellings before a sale can be made and settled are also often not accounted for,” he says.
“There are costs associated with this process, such as surveyor fees, legal fees, council fees and Land Titles Office fees. The whole process can add between $15,000 and $20,000 of unexpected costs right at the end of the project – often when money has run out,” says Couvaras.
“The process can take six to eight weeks if you are not well organised. Holding costs on the dwellings before a sale can be made and settled are also often not accounted for,” he says.
Are there any other additional costs people might not be aware of?
“Yes – council and town-planning fees may be more,” says Homer.
You’ll also have double the amount of finishings, windows, electrical and plumbing works, he says.
“Most of the hidden costs lie in the duplication of services, such as power, water and the internet,” says Couvaras. “Apart from the actual cost of installing these, utility providers charge all kinds of fees for connections, disconnections and approvals for additional dwellings.”
“Yes – council and town-planning fees may be more,” says Homer.
You’ll also have double the amount of finishings, windows, electrical and plumbing works, he says.
“Most of the hidden costs lie in the duplication of services, such as power, water and the internet,” says Couvaras. “Apart from the actual cost of installing these, utility providers charge all kinds of fees for connections, disconnections and approvals for additional dwellings.”
Project by Robinson Architects; image by Alain Bouvier
Which sites are suitable for duplexes?
Couvaras says:
Which sites are suitable for duplexes?
Couvaras says:
- Most local governments have specific requirements for duplex sites. Minimum lot sizes and widths are common and it pays to check these carefully. Many also restrict dual occupancies on internal or battleaxe lots.
- A width of 18 to 20 metres is optimal for a standard side-by-side duplex, but they can fit on a 15-metre-wide block.
- Corner sites are ideal as each dwelling can have its own frontage and, if large enough, they can be detached. They can also have separate vehicular access.
- A creative architect can fit a duplex on any site – we have even been able to use a triangular-shaped block.
Builder: Futureflip
Homer says:
Homer says:
- Ideally the site needs to be large enough to accommodate two reasonably sized buildings without over-reaching the coverage restrictions set by council.
- If you are looking to subdivide the land into two lots, councils will also set minimum lot sizes. Density restrictions may allow multiple dwellings on a single lot, which is ideal for a duplex.
- Is the site zoned for a duplex?
- What is the ratio calculation set by the local authorities for the size of the site? This will govern the size of the buildings and may determine whether you can have two- or three-bedroom units or a combination.
- What’s the aspect? You’ll want each unit to have as much northern exposure as possible and little from the west.
Which sites are not suitable for duplexes?
Homer says:
Homer says:
- Small sites (under 150 square metres).
- Previously subdivided sites.
- Sites with limited street frontage.
- Poor orientation and overshadowing by adjacent buildings.
- Very wide, shallow sites.
- In many council areas, sites that slope down from the road are not suitable due to drainage issues.
Render of the interior of a duplex by Russell Rice at Archisoul Architects
What are some of the unique challenges a duplex presents?
Homer says:
What are some of the unique challenges a duplex presents?
Homer says:
- Additional costs during the build phase such as doubling up on elements including kitchens and laundries.
- If building in partnership, disagreements may arise when selecting design and style aspects.
- Getting adequate natural light and ventilation can be difficult if building side-by-side due to the firewall splitting the dwellings, which cannot have openings.
Project by Robinson Architects; image by Alain Bouvier
What are the main design challenges?
Couvaras says:
What are the main design challenges?
Couvaras says:
- Orientation: if the backyards don’t face north, one or both dwellings will suffer from a lack of sunlight.
- Where council or site conditions require the garages in the centre, a number of difficulties arise. The first is the shared driveway and potential for conflict between the two residents. The second is the amenity of the dwelling arising from the entrance at the side. The ability to separate the driveways and create a central entry is key to a well-designed duplex.
- Noise between dwellings shouldn’t be a problem: building codes have now adequately addressed this.
What are some smart ways architects can overcome these challenges?
Couvaras says:
Couvaras says:
- A staggered building setback can be used to get light into the overshadowed side.
- Courtyards and voids in the centre of the dwellings can boost light. These are especially successful in bigger dwellings where the plan becomes long and dark.
- Designing the dwellings so stairs and service rooms are located on the party walls allows for living rooms and bedrooms on the outside walls. This is not only helpful for daylight, but also in reducing noise. It is always better to solve a problem through design rather than rely on materials or add-on solutions.
- Skylights are the only other option for ‘dark-side’ dwellings.
Project by Robinson Architects; image by Alain Bouvier
What sort of approvals do you need?
Couvaras says:
What sort of approvals do you need?
Couvaras says:
- Subdivision approval so the second dwelling can be sold separately.
- Some councils have teams that specialise in approving duplexes, which means they can process approvals in similar timeframes to a single dwelling.
- In most council areas in NSW, duplexes require council approvals. State government has prepared a ‘complying development code’ that can allow for a simpler and faster approvals process on certain types of land.
Your turn
Have you ever lived in or built a duplex and what was your experience like? Tell us in the Comments below, like this story, save the images for inspiration, and join the conversation.
More
Want more expert insights? Don’t miss: So You Want a Sustainable Kitchen? Everything You Need to Know
Have you ever lived in or built a duplex and what was your experience like? Tell us in the Comments below, like this story, save the images for inspiration, and join the conversation.
More
Want more expert insights? Don’t miss: So You Want a Sustainable Kitchen? Everything You Need to Know
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Every house, no matter how small, needs a double garage to be really useful and valuable to the occupants. A duplex should have 2 double garages as it I is almost guaranteed that at least 2 cars will belong to each unit. The extra effort is very well worth it for day to day living and for a tidier yard and street. An estate agent told she can sell a duplex in less than a week if it has a double garage.
Thanks for the article, very helpful!
Can a site be split unevenly, ie: 60% / 40% ratio.
The site i have is 750 m2 and minimum lot size set by council is 450 m2 hiwch makes it unsuitable to subdivide as 2 lots on their own. Minimum requirements for duplex though are 585 m2 which allows us to build a duplex. Our preference is to make one side bigger (for us to live in) and another one slightly smaller for renting out. Appreciate your comment on this.
Cheers
The need for a double garage varies wildly with the location and demographics. In city areas, or at least those with good public transport, or car share oportunities, households may often have one or zero cars, or prefer bike storage instead. It is 2024- I am aware that it is not possible everywhere, but reducing car ownership and consequently the wasted real eastate dedicated to their storage, as well as cost of living, and environmental benefits, surely has to be both important and hopefully aspirational!?