Dual occupancy on an RZ1 block

Dual occupancy is the question most Canberra house blocks now face, and it became a real question on 1 July 2026 rather than a theoretical one. Before MPA 04 a second dwelling in RZ1 was capped at 120 m² and the block had to be at least 800 m². Both are gone. A second dwelling can be full size, and block area no longer gates whether you may build one at all.

What follows is what it costs and what stops it, in the order the numbers actually decide.

1. The Lease Variation Charge — almost always the largest number

Adding a dwelling to a Crown lease triggers the Lease Variation Charge, and it is payable to the Territory whether or not the project ever makes money. It is set per suburb, not per block, and the range is enormous:

The payable column assumes the missing middle remission, which halves the codified charge in RZ1 and RZ2 until 2029. It is the largest change to ACT infill economics in years and it is not automatic — the DA must be approved by 30 June 2029 and the dwellings completed by 31 December 2030.

Two things about this charge catch people out. It is struck against the suburb, so a cheap block in an expensive suburb still carries the expensive charge. And it is not a proportion of what you paid, so buying well does not reduce it.

2. The frontage, which decides more schemes than the area does

Area is the number in the listing and frontage is the number that kills projects. Two dwellings side by side need a driveway, manoeuvring, and two addressable entrances. Below roughly twenty metres that gets difficult; below fifteen it usually means one dwelling behind the other, which is a longer driveway, more paving, and a rear dwelling with a worse aspect.

3. What the block can actually hold

Plot ratio in RZ1 is 0.50 — so a 580 m² block yields 290 m² of gross floor area across the whole site, and two dwellings inside 290 m² is two small dwellings rather than two houses. On 1,105 m² the same ratio gives 552 m², which is two comfortable ones.

Two cautions, and the second matters more than most published advice admits. Plot ratio is now guidance rather than a mandatory requirement. Site coverage is the opposite — it became mandatory under the Residential Zone Policy, and on a constrained block it, not plot ratio, is usually the binding control. This tool does not compute site coverage, so treat any GFA figure here as an upper bound for sanity-checking revenue, never as a cap you can design to.

Also worth discarding: the formula 140 ÷ block area + 0.15 still circulates widely for RZ1 dual occupancy. It is two plan versions out of date and understates buildable area by about a third.

4. The things that help

• You almost certainly do not need a developer licence. The ACT property developer licence becomes mandatory on 1 October 2026 at three dwellings. A dual occupancy sits below that threshold.
• Stamp duty has moved in your favour. From 1 July 2026 it was abolished for first home buyers and removed on new unit-titled homes for owner-occupiers — see buyer incentives for which of them applies to a purchaser of the second dwelling.
• The DA need not be on the critical path. The Pattern Book offers pre-approved designs for $1,000 with no development application, which is the most reliable way to protect the 2029 remission deadline.

The order to check them in

Zone first, because RZ1 and RZ2 are the only ones the remission reaches. Then the charge for that suburb, because it is the largest number and it is knowable in seconds. Then frontage, then site coverage. Unimproved value comes last and is a floor rather than a valuation.

Every one of those except site coverage is on the property page for any ACT address, and there are worked examples on real blocks if you would rather see it done once before doing it yourself.

Can you build a dual occupancy on any RZ1 block in Canberra?

Since MPA 04 commenced on 1 July 2026 there is no minimum block size in RZ1 and no 120 m² cap on the second dwelling. Whether a particular block works is decided by frontage, site coverage and the Lease Variation Charge for that suburb rather than by a threshold area.

How much does a dual occupancy cost in Canberra?

The statutory cost is the Lease Variation Charge, which is set per suburb and ranges from about $26,250 payable in Greenway to $173,000 in Forrest once the missing middle remission halves the codified figure. Build, DA and holding costs sit on top of that and are specific to the scheme.

Do I need an ACT property developer licence for a dual occupancy?

No. The licence becomes mandatory from 1 October 2026 at three or more dwellings, and the trigger is lodging the development application. A two-dwelling development sits below the threshold.

What is the plot ratio for RZ1 in Canberra?

0.50 for multi-unit housing, and it is now guidance rather than a mandatory requirement. Site coverage is mandatory instead, and on a tight block it is usually the control that binds first.