Will Your R20 Block Become Subdividable? The 50,000-Lot Question

Somewhere in Perth there are around 50,000 blocks that cannot be subdivided today and would become subdividable if the announced R-Codes reform proceeds. The owners of most of them do not know it yet. This article gives you the arithmetic to work out whether your block is one of them, in about two minutes.

The two-number test

Find your R-Code (your council can tell you, or use our free checker). Then apply two numbers:

At R20, today’s rules require each dwelling to have 350 sqm as a minimum AND the block to provide 450 sqm per dwelling on average. The average is what stops most blocks: a 720, 780 or 855 sqm block clears two lots on the minimum but fails the 900 sqm the average demands.

The announced reform removes the average for R20 and below. The test becomes the minimum alone.

So for R20: if your block is between 700 and 899 sqm, you are in the window. Today: one dwelling. Under the reform as announced: two. Blocks of 900 sqm and above already clear two under current rules; blocks under 700 sqm stay single under both.

The same logic applies down the codes: R17.5 (minimum 500 sqm), R15 (580 sqm), R12.5 (700 sqm) and R10 (875 sqm) each have their own window where the abolished average would change the answer.

What being “in the window” is actually worth

A block that flips from one dwelling to two does not just gain a second lot; it changes buyer pools. Single-home blocks sell to home buyers; subdividable blocks also sell to developers and investors, who price the second lot in. That is why the reform announcement matters to owners who never intend to develop: it can reprice the asset underneath them.

But the announcement is not law, and paper yield is not real yield. Sewer position, easements, frontage and council policies still decide whether the second dwelling actually fits. An 855 sqm block with a sewer main through the backyard and a heritage-listed front elevation is still an 855 sqm block with problems.

Check it properly, for free

Our R-Code check runs your block against today’s rules and, where the announced reform would change your outcome, shows you both results side by side, clearly labelled as proposed and not law. It also lists the constraints that decide real projects, and what the pathways would indicatively cost using live Perth builder pricing. No sign-up, no charge.

If your block is in the window and the answer matters to your plans, the next step is verification: title search, sewer plans, comparable sales. That work takes days, the consultation window will not stay open forever, and owners who know their numbers move first.

Frequently asked questions

How do I find my R-Code? Your council’s planning maps show it, PlanWA shows it, or enter your details in our free checker.

My block is 910 sqm R20. Does the reform help me? You already clear two dwellings under current rules. The reform as announced does not add a third at that size (the minimum is 350 sqm, so 1,050 sqm is the three-lot line).

Is a corner block treated differently? Corner lots can have additional options under some council policies, and truncations are handled specifically in the R-Codes. Worth checking individually.

When will we know if the reform is real? Consultation is expected late 2026 with gazettal targeted mid-2027. We track every R-Codes change and our tool is updated the day rules change.