Building a duplex


Just wondering if anyone has ever bought a house and made it into a duplex?

I see a lot of houses converted this way in the expensive Eastern suburbs of Sydney. ie Bellview Hill.

I would like to buy an older house, renovate it fully, make it into a duplex (ie semis) ... sell one and live in the other?

Basically the ideal situation of course is: buy old house for $400k (NOT in Bellview Hill. You can't buy a dog kennel for that price there!!! ;) ), spend 300k making it into a modern 2 storey duplex. Sell the new duplex for 700k, pay off the whole mortgage and youhave a house fully paid off to live in.

Of course I understand this is a utopian scenario, but here is where I'd like some feedback from peoiple who know of people who have done this, or more importantly have done this themselves.

I realise there will be a question of "Why not knock it down and build 2 units". Reason is I think it would be a lot harder to get permit for that. This is an educated guess and not a fact, so please correct me if I am wrong.

Thanks in advance!


Doesn't seem there has been much of a reply to this post. Which is a shame because I would have been interested in the disucussion. Unfortunately I'm not someone who can really help you with your scenario but am just interested in the basic idea.

I think you acknowledge in your post that the situation or outcome you describe is somewhat utopian. The figures you refer to are also not what I would think is realistic pricing in the eastern suburbs of Sydney. Even in the current market where demand has dropped significantly.

Even in the less sought after areas of the eastern suburbs I have never heard of a sale in recent years where the price was 400k or anywhere near. Even for land value only. Not for houses/blocks. Not even Semis. In Maroubra, away from the water towards Maroubra Junction with no water views and potential city views at best there is currently a block for sale, 260m2 (approx) with a knock down residence on it, in a good part of town, that they are asking mid to low 700's for. I'd be surprised if they get that price considering the size of the block wouldn't give you much room to build on. But that's an indicator of land value anywhere in the eastern suburbs. Yeh sure you can go further inland or further south, say Matraville, Botany, Little Bay direction and prices will come down a bit. But still, you're lucky to get a decent two bedroom unit in a decent area for 400k.

Now please don't take this as an attack. I'm just letting you know because if you intend to look at your stated option further you'll really need to know what you should expect to pay for property. I like the idea in theory and if the numbers were to add up might be worth looking at. If anyone else around knows more about this topic please let us know your experience / opinions? I'm definately not an expert on it.

Good luck with it. Let us know how you go.

Hi Mark, no offence taken ;)

Actually I was a bit off in the suburb naming... I meant the St George area. More specifically Rockdale City Council area.

As you rightly pointed out, even in Maroubra a 550sqm block would be around 900k (close to the water).

I have done quite a bit of research, even put in 3 offers on blocks in the Brighton area, but so far have not picked anything up.

I can get a block of 550-600sqm for around 550-600k. Basically $1000 per sqm. If I take an estimate of $7000 per sq, to build 2 x 24sq units/duplex would be about $336,000.

Total cost would float just above the 900k mark for the purchase + costs + building + holding costs. Currently a well built new duplex is fetching 800+k. One was sold for 805, another for 860. Considering a 9 month project time, and growth of around 12% in that time (this area is starting to pick up in growth!) I think a price of 850 is not unreasonable (esp. for a quick sale). Therefore after all costs + the "net" situation would be around 70k. With anohter duplex/unit still available to live in (or sell).

I am arranging to speak to 3 developers at the moment to go through the feasiblity study. On the weekend I drove around the area and in 15 mins found literally about 15 candidates for what I want to do!!! I have NO DOUBT IN MY MIND (you can see I am reading "Think and grow rich" but Napoleon Hill right now ;) ) that this project is possible. It's a matter of finding the right people to do it with.

I am going to suggest a 40% equity share to the builder on the sale of one of the units in exchage for his services. (ie. HE covers the cost of building). If he builds a quality unit, and it fetches 900k, he gets $360k instead of the 336 if I paid for it. A nice little 24k bonus. :)

Thanks for the feedback :)


the places you are looking to buy, are they old houses that you would remove/knock down and have you allowed costs for this?

have you spoken to council regarding heritage listings and approval to build 2 on 1 block, you may need a certain number of meters before they will allow a duplex.

This can vary from street to street and even block to block. Some councils have a map you can buy showing density permits.

Macca :)

Also look under the dual occupancy provisions from council. This would apply to what you're suggesting with regards to converting an old house into two seperate dwellings.

We are doing a dual occupancy , and our advisor gave one example where a run down two story corner house was converted into a dual occ. with each dwelling being on one level. The total conversion was around 250 k. The owners sold one for > 1 mill and continued to live in the other ( Syd North shore ) .

Fire regulations come into play when you have two dwellings in one building as do the other things mentioned.

See change

I don't fully understand the term "dual ocupancy". Does it actually mean splitting the title allowing separate sale of each, or having two on the same title? Also, if you know, what is called "attached dual occupancy"?

Say cheese :p

Originally posted by Lotana
I don't fully understand the term "dual ocupancy". Does it actually mean splitting the title allowing separate sale of each, or having two on the same title? Also, if you know, what is called "attached dual occupancy"?


Dual occupancy is putting two houses on the one title. Once it's been dual occ'd, you can subdivide - two houses on strata title or community title.

I've read through the planning papers for the council and I found which streets are ok to build dual occupancy on.

From the research that I have done so far I gathered that I need to do a LOT more research!!! :eek:
Originally posted by Lotana

How would you define "community title"?

Say cheese :p


The simplest definition is that strata title goes up, and community title goes across. So units would be strata, and townhouses – community. Like all things, this is fairly rubbery – Adelaide now wants everything to be community titled.


You could revise your opinion on 12% growth in 9 months, i think in the current market and especially the overheated Sydney Eastern Suburbs market you should plan for zero growth or possibly even negative growth. Be careful and get advice.

Also you might look at regulations ruling on land/dwelling ratio. You might need to buy a bigger block than you think if the local council has a tough ratio. (say 50%/50%)

The local council i am living in at the moment (Gosford) recently toughened up the land/dwelling ratio to discourage spec. builders
buying knock downs and building duplexes/villas. The council was of the opinion that the suburb was turning into villa city (and they were right.)

And they changed it just as i ws looking for a property to do the same, as always.........perfect timing.

Dual occ. is 2 properties on one block of land, to separate the titles can be done either strata or Torrens title if its a subdivided block and then it becomes two blocks with two houses with two titles just like two house blocks in a street. I did one years ago and the paper war was awesome.
Originally posted by brains
The council was of the opinion that the suburb was turning into villa city (and they were right.)

And they changed it just as i ws looking for a property to do the same, as always.........perfect timing.

I always ask myself, "Self, if I finally have heard about this and understand it, is it too late?"

By the time retail investors are promoted a scheme it is often on its last legs.


Paul Zag

Not all Dual occs can be subdivided.

It varies from council to council . Blacktown used to be ok , but no longer is. Parramatta isn't but maybe become ok. Ryde isn't. Kuringai is ok ans is hornsby. Minimum block sizes vary significantly as do set backs and accesses.

Ku ring gai which has probably the strictest ( and unreasonable ) guidlines, has had several rejected applictions passed by the land and environment court. This may sound more expensive , but a block that doesn't fit into their guidlines is going to sell for a lot less than one that conforms to the guidlines.

Attatched Dual occs are when the two dwellings are physically attached to each other. This could either be in the form of one descrete building being subdivided internally into two dwelling , or where the two dwelling may share a common wall ( preferably where the garages meet)

Attached dual occs require smaller blocks of land , but are obviously less attractive to some people because of the attachement

See change
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i did a dual occ. & subdivision in the parra council area about 6 years ago, so they must have changed the ruling and are going to change it back again....dont you love local councils.

That is my understanding. I havn't check with parramatta council myself , but was relying on a normally reliable source.

Obviously , anyone should do their own checks prior to acting on information on this ( or anyother ) website.

Even council staff will make mistakes or do not necessarily give people the full picture if it is against council policy. We did a subdivision in Ku ring gai after I had been told by the council that the block was not subdividable. We didn't need to go tto the Land and environment court. We presented them with a proposal that was reasonable and in keeping with the local area and had no problems at all ( except for a ten month wait while two meters of sewerage line was planned , approved , quoted for , constructed , inspected and finally certified.... :rolleyes: :eek: )

see change
Hi Iggy,

My brother in law had the same idea - offer a builder one unit in exchange for building some units.

The only hurdle that you may come across in this scenario is Home Owner's Warranty Insurance that the builder is required to take out to protect the client's interests.

These days HOWI is considered to be the builder's bread and butter - no insurance means no work.

The primary insurer, Dexta, makes builders practically jump through hoops to get a policy today, and they have scrapped annual blanket policy; these days policies are issued on a job by job basis. There is another large insurance underwriter, but Dexta is considered to be the easiest to deal with.

The builder is required to submit with each application all the jobs completed, value of contracts, type of work and profit made on each job, amongst other things, for the last 12 months, and they mainly look at the cash in the bank factor when assessing the builder's "insurance servicability".

So, alot of builder's may just want the cash to build rather than take the equity.