New house floor areas have climbed for four years straight, against every assumption about affordability. A new Census variable is about to measure part of the reason, and miss the rest.
The average new house completed in Australia in 2024-25 measured 241.5 square metres. Four years earlier it was 230.0.
That is an extra 11.5 square metres, about 5 per cent, and the highest figure in the published national series since 2011-12. It happened through the tightest affordability window in a generation, while blocks kept getting smaller.
The numbers come from the ABS average floor area data cube, published once a year inside the December quarter Building Activity release. Two things are worth knowing before leaning on them. It is a completions average, so it describes homes finished in the year rather than homes designed in it, and it excludes records where floor area was not stated.
New houses are getting bigger while the blocks get smaller
It is not only detached houses. Townhouses went from 166.4 to 174.5 square metres across the same two years. Apartments went from 116.1 to 125.3. The Australian Capital Territory now averages 298.2 square metres for a new house and Western Australia 256.8. Tasmania went the other way, down to 165.8.
Now set that against the land. ABS analysis of house approvals across the five largest capitals found the average site area fell from 496 square metres in 2012 to 432 square metres in 2021, a drop of 13 per cent. Over the same decade, average floor area fell by 3 square metres, or about 1 per cent.
So the block shrank and the floor plate did not, and over the last four years the floor plate has started climbing again. Every extra square metre now has to come out of setbacks, site cover or a second storey.
That runs against a lot of the commentary on Australian construction industry trends, which has assumed the affordability squeeze would push the new home smaller. It has not. Something else is pulling the other way.
The floor area data does not say what. It only says the direction. But a bigger footprint on a smaller block, in a market where more households contain a third adult, is not a coincidence that needs much explaining.
The 2026 Census counts multigenerational households for the first time
That third adult is about to get measured.
The 2026 Census dictionary, released on 21 July 2026, lists multigenerational household composition as a new variable, derived from the relationship question every household answered on Census night, 11 August 2026. Until now, anyone wanting a national count had to buy custom tables from the Bureau. From this Census, the number simply exists.
The Australian Bureau of Statistics defines a multigenerational household as three or more generations from the same family line who usually live in the same dwelling. The generations have to sit in a vertical line, running through children, parents, grandparents and great grandparents, and that line has to include the household reference person.
A household that skips a generation still counts, so a child living with a grandparent and a great grandparent qualifies even with the parent generation absent. The variable then splits into one family multigenerational households and two or more family households, which is how a household with a separate older couple inside it gets recorded.
The Bureau is also explicit about what does not count. Households with fewer than three generations are not multigenerational, and adult children living with their parents are not counted unless a third generation is present.
What the ABS counts as a multigenerational household
Three or more generations from the same family line who usually live in the same household, in a vertical line that includes the household reference person. The line runs through children, parents, grandparents and great grandparents. A household that skips a generation still counts where three generations remain. Two generations do not. Adult children living with their parents are not a multigenerational household unless a third generation is present. Source: ABS Census dictionary 2026, multigenerational household composition.
The definition is narrower than the brief a builder gets
Two of the most common shared household arrangements in this country sit outside that definition.
An adult child still at home in their thirties is two generations. A widowed parent moving in with a couple whose own children have left is also two generations. Neither will appear in the multigenerational count.
Both produce almost exactly the same request at the design table. A bedroom with its own bathroom. Some acoustic separation from the main living zone. A door that closes. In a fair share of cases, a kettle and a sink.
The number, when it lands, will be a floor rather than a measure of demand. It counts the households where three generations are under one roof. It does not count the much larger group where two households have folded into one dwelling.
Living with other relatives is growing faster than the population
There is a second ABS measure that picks up more of this. In its Household and Family Projections, released in June 2024, the Bureau tracks people living with other relatives, a category it describes as including elderly parents living with their adult child’s family, and adult siblings living together.
- 636,667 Australians were in that arrangement in 2021
- Between 904,945 and 1,041,210 are projected to be by 2046
- Across the same period the total population is projected to grow 32 per cent, from 25.7 million to 33.9 million
On those published endpoints, the arrangement grows by roughly 42 to 64 per cent while the population grows 32 per cent. That calculation is ours rather than an ABS headline, but the direction is the Bureau’s own.
The age skew is where it gets practical. Among people aged 80 and over, 10 per cent were living with other relatives in 2021. The projections put that at 13 to 17 per cent by 2046. For people in their fifties, the figure sits around 11 per cent and holds.
The ABS is careful to say these are projections rather than predictions, and that they illustrate what would follow if current living arrangements persisted. Worth holding onto. What they are not is a story about households thinning out. Average household size was 2.57 in 2021 and is projected at 2.55 by 2031. The average is flat. The distribution underneath it is not.
The number, when it lands, will be a floor rather than a measure of demand.
The second kitchen is the line between a floor plan and a second dwelling
Where a house can absorb an extra household is a planning question before it is a design one, and the line falls in a specific place.
Inside the main dwelling there is no floor area cap on a guest wing, a second living zone or a second ensuite. There is also no separate tenancy, no separate meter and no rental income. Once that wing becomes self contained, with its own kitchen, bathroom and entry, it is a secondary dwelling, and a different set of rules applies.
- In New South Wales, the Housing SEPP caps a secondary dwelling at 60 square metres, unless another environmental planning instrument permits a greater area on the land, and the lot cannot be subdivided.
That exception is doing real work. It is how secondary dwellings near the Western Sydney Airport were opened up at a larger size than the standard state allowance.
- In Victoria, since Amendment VC253 in December 2023, a small second dwelling of 60 square metres or less needs no planning permit in most cases. It always needs a building permit, it cannot connect to reticulated natural gas, it cannot be subdivided or sold separately, and anyone may live in it or rent it. An attached one requires fire separation, and anything over 60 square metres falls outside the definition entirely.
- In Queensland, the restriction on who may occupy a secondary dwelling was removed from 26 September 2022. Size caps remain a matter for each council planning scheme rather than the state.
That last point is shifting. The new Queensland Housing Code covers detached houses and secondary dwellings, and councils can adopt it across a three year transition that started on 1 September 2026.
The practical effect of all this is a fork. Sixty square metres of separate dwelling, with its own approval path, its own services and a rentable tenancy at the end of it. Or an uncapped wing inside the main roof that is cheaper per square metre and carries none of those rights. The second option is where a lot of those extra square metres have been going.
Most of the country already builds the accessible part by code
There is one piece of this that has quietly stopped being an upgrade.
Part H8 of the National Construction Code 2022 took effect on 1 October 2023, and on 1 October 2024 in Tasmania. It applies to Class 1a buildings and calls up the livable housing design standard. In practice that means a step free access path, a level entrance door, internal doors and corridors on the entrance level that allow unimpeded movement, a sanitary compartment and shower built to the standard, and bathroom and toilet walls constructed so grabrails can go in later without stripping the linings.
New South Wales is the exception. The NSW variation page reads that the Part has deliberately been left blank, and states that livable housing design requirements do not apply to Class 1a buildings there.
Everywhere else, the hardest and least visible part of an ageing in place wing is already in the base spec. The circulation is sized. The walls are backed. What the code does not deliver is separation, and separation is the thing families are actually asking for.
What the count will and will not settle
When the household data from the August count is released, we will have a real national number with state and small area breakdowns, and the argument about whether this is a trend or a marketing line largely ends.
It will not settle the design question. A three generation count tells you how many homes have grandparents, parents and children under one roof. It says nothing about the adult child in the converted garage, or the parent in the front bedroom with a kettle and a bar fridge, and those households are buying the same thing: distance inside a dwelling.
The Census will describe the household. The floor plan has to hold it. Those are not the same shape, and the gap between them is where those 11.5 square metres have quietly gone.
The Good Builder Take
The floor area number is the one to watch, because it is measured rather than projected and it moves every year. The Census number will be quoted more, and it will be too small. Read it as a lower bound, because the design pressure sits in the two generation households the variable was never built to capture, and those are the briefs already walking through the door. The useful question for anyone quoting this work is not how many multigenerational households exist. It is whether a client wants a separate dwelling with a 60 square metre ceiling and a tenancy, or an uncapped wing under the main roof with neither. That fork decides the approval path, the services, the cost per square metre and the resale story, and it is better settled at concept than at contract.
Frequently asked questions
Bigger, over the last four years. ABS Building Activity data puts the average floor area of a completed new house at 230.0 square metres in 2020-21 and 241.5 square metres in 2024-25, an increase of about 5 per cent and the highest figure in the published series since 2011-12. Townhouses and apartments grew over the same period too.
Yes. ABS analysis of new house approvals across the five largest capital cities found average site area fell from 496 square metres in 2012 to 432 square metres in 2021, a drop of 13 per cent. Average floor area over that same decade fell by only 3 square metres, or about 1 per cent, and has risen since.
The ABS counts a household as multigenerational when three or more generations from the same family line usually live in the same dwelling, in a vertical line that includes the household reference person. Two generations do not qualify, which means adult children living with their parents are not counted unless a third generation is also present. This is a new variable for the 2026 Census.
It depends on the state. New South Wales caps a secondary dwelling at 60 square metres unless another environmental planning instrument allows more on that land. Victoria uses the same 60 square metre figure for a small second dwelling, above which the exemption from a planning permit no longer applies. Queensland sets no state size cap, leaving it to each council planning scheme, though the new Queensland Housing Code gives councils a consistent standard to adopt from September 2026.
In most of the country, yes. Part H8 of the National Construction Code 2022 has applied to new Class 1a homes since 1 October 2023, and since 1 October 2024 in Tasmania. It covers step free access, entrance doors, internal circulation on the entrance level, bathroom provisions and wall reinforcement for future grabrails. New South Wales did not adopt it for Class 1a buildings.
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Last updated: 15 September 2026. Floor area figures are from the ABS Building Activity average floor area data cube published April 2026, covering financial years to 2024-25. Living arrangement figures are projections published June 2024 and will be superseded by 2026 Census household data.
General information only. This article reports on published data, planning instruments and code requirements at the date shown. It is not legal, planning or building advice, and it is not a substitute for checking the current requirements that apply to a specific site with the relevant council, a qualified town planner or a registered building certifier. Rules vary between states and between local government areas, and they change.
Author: TGB Editorial
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