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Modular duplex costs
| Duplex kit, 2+2 bedrooms | A$145,280 for 155.48 m², materials only[1] |
|---|---|
| Duplex kit, 3+3 bedrooms | A$303,710 for 281.96 m², materials only[1] |
| Installed modular duplex | No published figure located |
| NSW dual occupancy | Permitted with consent in R2 zones state-wide since 1 July 2024[2] |
| NSW planning risk | Two manufactured homes on one lot can be treated as a manufactured home estate[3] |
| *Kit prices include GST and exclude assembly, floor, delivery, approvals, site works and connections. | |
No installed price for a modular duplex was located in Australian published sources. The closest published figures are for kits: one supplier lists a two-plus-two-bedroom duplex kit of 155.48 m² at A$145,280 and a three-plus-three-bedroom kit of 281.96 m² at A$303,710, for materials only.[1] In NSW the bigger cost risk is planning, not price: two factory-built homes on one lot can be treated as a prohibited manufactured home estate.[3]
A duplex — in planning language usually a dual occupancy — is two dwellings on one lot, either attached or detached. NSW has permitted dual occupancies with consent in R2 low density residential zones across the state since 1 July 2024.[2] Building them off site sounds like an obvious fit: two repeatable homes, one site preparation, one crane booking. What is actually published is thin, and the most important cost item is one that rarely appears in a quote.
What is published on price §
| Design | Bedrooms | Area m² | Full kit | Floor kit (extra) |
|---|---|---|---|---|
| Woy Woy | 2 + 2 | 155.48 | A$145,280 | A$31,670 |
| Double Bay | 3 + 3 | 281.96 | A$303,710 | A$46,460 |
Each design is two mirrored dwellings sharing a dividing wall.[4] These are kit prices — materials delivered for assembly on site — and exclude assembly, delivery, approvals, site works and connections.[1][4] How a kit price relates to a finished house is set out in Kit home costs, where the same supplier's estimate for a finished four-bedroom single home is roughly double the materials cost.
For volumetric modular duplexes — two homes manufactured as modules and craned onto the site — no published Australian price was located. Single-dwelling modular prices by size are collected in Modular home cost by number of bedrooms, but two single-dwelling prices cannot simply be added together: shared walls, shared site works and two sets of connections change the arithmetic in ways no located source quantifies.
The planning risk in NSW §
Under NSW planning law, a manufactured home is a self-contained dwelling built off site in one or more sections and installed on site, and a manufactured home estate is land on which manufactured homes are, or are to be, erected.[3] An estate may only be carried out where a caravan park may be carried out, and local environmental plans commonly do not permit caravan parks in ordinary residential zones — so where a council treats two factory-built homes on one lot as an estate, the proposal is a prohibited use that cannot be approved, however well designed.[3]
That is not hypothetical. At Bulli, Wollongong City Council refused two applications over two years for a second modular home on a subdivided lot beside an existing modular home, on the basis that its local plan permits one modern method of construction home per allotment and more than one is a manufactured housing estate; the applicants were paying rent and a mortgage throughout.[5] Councils apply the definitions inconsistently, so an approval for a similar product in one council area carries no weight in another.[3]
For budgeting, this means the first cost of a modular duplex in NSW is establishing — before paying a manufacturer — how the council will classify the proposal. Reforms to how prefabricated buildings are approved in NSW, and their commencement status, are tracked in NSW Building (Approvals and Practitioners) Act 2026.
Site rules that shape the design §
Where the NSW Low and Mid-Rise Housing Policy's non-discretionary standards apply, a dual occupancy needs a lot of at least 450 m² and 12 m wide, with a maximum floor space ratio of 0.65:1, a maximum height of 9.5 m and one car space per dwelling; subdivision in R1, R2 and R3 zones is permitted down to 225 m² and 6 m width per lot.[6] The standards do not apply on land affected by certain hazards and constraints.[6]
Those numbers matter for modular design because module widths are fixed by road transport. A narrow lot that suits two site-built homes may not suit two sets of transportable modules side by side. How transport limits shape floor plans is covered in Modular home floor plans and customisation.
The ability to subdivide is also the main financial difference between a dual occupancy and a granny flat, which cannot be separately titled — see Dual occupancy vs granny flat.
Costs that scale with two dwellings §
No located source gives modular-specific figures for these, but each is covered generally elsewhere on this site:
- Council fees and contributions — see DA fees and developer contributions.
- Service connections for two dwellings — see Service connections.
- Transport and craneage for more modules — see Module delivery, transport and craneage.
- Footings under both dwellings — see Foundations for modular and prefab homes.
What is not covered here §
No published installed price for a volumetric modular duplex in Australia was located, and no figure is estimated here. Dual occupancy rules outside NSW are not covered on this page. Subdivision costs (survey, titling and legal fees), strata versus Torrens title choices, and the tax treatment of building a duplex to sell or rent are not covered by the sources compiled here. How a particular council will classify two factory-built homes on one lot can only be confirmed with that council or a planning professional.
Inclusion of a supplier's prices on this page is not an endorsement.
Sent to info@modularlivingaustralia.com.au and handled by a person. See Privacy.
References §
- iBuild Kit Homes — N3 Price Guide, version dated 1 May 2026. Prices include GST, are for material supply only and are based on supply to metropolitan Melbourne; delivery and permit costs are excluded. Lists two duplex designs, the Woy Woy (2+2 bedrooms, 155.48 m²) at A$145,280 for the full kit with an optional floor kit of A$31,670, and the Double Bay (3+3 bedrooms, 281.96 m²) at A$303,710 with an optional floor kit of A$46,460. Supplier-published commercial guidance. i-build.com.au/wp-content/uploads/pdf/kithomes/Pricelist/iBuild%20Kit%C2%A0Homes%C2%A0N3%C2%A0Price%C2%A0Guide%C2%A020260501%20V100.pdf
- NSW Department of Planning, Housing and Infrastructure — Low and Mid-Rise Housing Policy, frequently asked questions — Stage 1 commenced 1 July 2024, permitting dual occupancies and semi-detached homes in R2 low density residential zones across NSW; Stage 2 commenced 28 February 2025. Defines low and mid-rise housing areas, describes the excluded land, explains how non-discretionary standards interact with local plans, confirms councils remain the consent authority for most applications, and sets out the complying development position and the affordable housing bonus. planning.nsw.gov.au/the-planning-system/housing/low-and-mid-rise-housing-policy/frequently-asked-questions
- The Good Builder — Trade media article, 29 July 2026, on when a second modular home becomes an estate in NSW. States that under the State Environmental Planning Policy (Housing) 2021, Schedule 7, a manufactured home is a self-contained dwelling built off site in one or more sections and installed on site, and a manufactured home estate is land on which manufactured homes are or are to be erected; that under section 122 of the SEPP an estate may be carried out only where a caravan park may be carried out, which local environmental plans commonly do not permit in ordinary residential zones; that a prohibited use cannot be approved; that councils apply the definitions inconsistently, so an approval in one council area carries no weight in another; and that Wollongong City Council refused a second modular home on a Bulli lot on this basis. Trade media summary of planning law, not an official source. thegoodbuilder.com.au/when-does-a-second-modular-home-become-an-estate-how-the-nsw-rule-works-and-where-it-applies/
- iBuild Kit Homes — Duplex designs page, modified August 2026. Describes each duplex as two mirrored dwellings sharing a dividing wall, positioned for multigenerational living, investment or dual occupancy; lists the Woy Woy (2+2 bedrooms, 1+1 bathrooms, 155.48 m²) from A$146,740 plus assembly and the Double Bay (3+3 bedrooms, 2+2 bathrooms, 281.96 m²) from A$306,750 plus assembly; and states a six-month price lock from contract signing. Supplier-published commercial guidance. i-build.com.au/?p=72649
- The Weekly Source — News article, 27 July 2026, citing the ABC. Reports that a couple seeking to build a second modular home at the front of a subdivided 1,840 m² lot at Bulli, NSW, beside a relative's modular home at the rear, had two applications refused by Wollongong City Council over two years, on the basis that its local environmental plan permits one modern method of construction home per allotment and more than one is a manufactured housing estate prohibited in the zone; and that the couple had been paying both rent and a mortgage during that time. theweeklysource.com.au/two-modular-homes-deemed-a-manufactured-housing-estate-under-planning-rules/
- NSW Department of Planning, Housing and Infrastructure — Low and Mid-Rise Housing Policy, summary of key provisions — non-discretionary development standards for dual occupancies in low and mid-rise housing areas: minimum lot size 450 m², minimum lot width 12 m, maximum floor space ratio 0.65:1, maximum height 9.5 m, one car space per dwelling, subdivision in R1, R2 and R3 at minimum 225 m² and 6 m width per lot. Also states the policy does not apply to sites affected by certain hazards and constraints. planning.nsw.gov.au/policy-and-legislation/housing/low-and-mid-rise-housing-policy/summary-of-key-provisions
Figures are as published by the sources above at their respective dates and are paraphrased summaries, not verbatim reproductions. Verify current pricing and rules directly with builders, lenders and planning authorities.