Possibly yes — but it depends on more than just the lot size.
A 400sqm block is on the smaller end of what most state planning frameworks consider for secondary dwellings. In NSW, the minimum lot size under the Complying Development pathway is 450sqm — which would rule out a 400sqm block on that pathway. But a 400sqm lot in Victoria, Queensland, or Western Australia may qualify depending on the zone and council.
More importantly: lot size is only one factor. The shape of your backyard, the setback requirements from your existing dwelling and boundaries, and your council's specific planning scheme all matter as much as the raw square metreage.
Consider two properties, both 400sqm:
Property A: 10m wide, 40m deep. The existing dwelling sits at the front 18m. That leaves a 22m deep backyard — more than enough to fit a secondary dwelling with compliant setbacks even on a narrow lot.
Property B: 20m wide, 20m deep. The existing dwelling takes up most of the depth with a small rear garden. After applying setback requirements, there may not be enough space for a compliant secondary dwelling.
Same lot size. Completely different outcomes. This is why a proper property-specific assessment — looking at the actual shape, configuration, and measurements of your backyard — is the only reliable way to determine eligibility.
Under the NSW SEPP Housing 2021 complying development pathway, the minimum lot size is 450sqm. A 400sqm lot does not qualify for this pathway.
However, a Development Application (DA) can be lodged for a secondary dwelling on a smaller lot — and councils assess these on a case-by-case basis. Some inner-city and established suburb councils have approved secondary dwellings on lots well below 450sqm where the configuration supported it.
Victoria does not set a single state-wide minimum lot size for secondary dwellings. Eligibility under VicSmart (the fast-track pathway) depends on the zone, overlays, and the proposed dwelling size. Many 400sqm lots in established Melbourne suburbs qualify.
Queensland's planning framework similarly does not prescribe a universal minimum lot size. Secondary dwellings are assessed against local planning schemes, which vary by council.
In Western Australia, the R-Codes (Residential Design Codes) govern secondary dwelling development. Many standard residential lots — including those around 400sqm in established Perth suburbs — qualify for secondary dwelling approval.
Even if the planning rules allow a secondary dwelling on your 400sqm block, the practical question is what can actually be built. On a typical 400sqm lot with an existing house occupying the front portion:
A 30–45sqm studio or one-bedroom dwelling is achievable on many 400sqm blocks with thoughtful design. This size dwelling can still generate significant rental income — particularly in high-demand metro areas where tenants prioritise location over space.
A 55–60sqm one-bedroom with outdoor area may be achievable on 400sqm lots with a generous backyard configuration and a narrower existing dwelling footprint.
The key constraints on a smaller block are:
A smaller secondary dwelling (35–45sqm) in a well-located metro suburb can still generate substantial income. Tenants in tight rental markets prioritise location above all else — a well-designed 35sqm studio in an inner suburb will be in high demand.
Reference rental income for compact secondary dwellings:
| City / Area | 35–45sqm Studio | 50–60sqm 1-Bedroom |
|---|---|---|
| Inner Sydney | $450–$600/week | $550–$750/week |
| Inner Melbourne | $400–$550/week | $500–$700/week |
| Inner Brisbane | $400–$540/week | $480–$640/week |
| Inner Perth | $420–$580/week | $520–$700/week |
On a 400sqm block in a good location, even a smaller secondary dwelling generating $450/week translates to over $23,000 per year in ongoing lease income.
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Planning requirements vary by state and council and are subject to change. This article provides general information only. Always confirm current requirements with a licensed certifier or town planner for your specific property.
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