It's the most fundamental question in strata: where does your lot end and where does common property begin? Almost 20 years on, Seiwa is still the leading NSW Court of Appeal authority on how stratum height notations on a strata plan actually define the lot boundary.
The case
The Owners – Strata Plan No. 35042 v Seiwa Australia Pty Ltd [2007] NSWCA 272
NSW Court of Appeal. The leading authority on stratum height boundaries in NSW strata plans.
The starting position
Under the Strata Schemes Development Act, every lot is defined as a "cubic space" shown on the strata plan. For most modern schemes, the boundary runs through the inside surface of walls, floors and ceilings — meaning the structure of the building is common property.
But many strata plans add a notation about a "stratum" — a specific height above the floor or below the ceiling that further defines the lot. The question in Seiwa: do those stratum notations actually define the boundary, or are they just descriptive?
What the Court decided
The Court of Appeal held that stratum height notations on the strata plan do define lot boundaries. They aren't decorative. They aren't descriptive. They are operative parts of the plan that tell you exactly where your cubic space of lot ends.
This matters enormously in practice because it means that everything above or below the stratum (anything outside the lot's defined cubic space) is common property — even if it looks and feels like part of your lot.
How it applies to townhouses and villas
Townhouse and villa strata plans often include stratum notations. Common examples:
- A balcony lot defined only up to a specific height above the slab — the airspace above belongs to common property
- A courtyard lot with a stated stratum above the paving — anything above (e.g. a pergola or shade sail attached to a wall above the line) is common property
- An "upper level" stratum that excludes the roof void — the roof and roof structure remain common property even though they sit on top of "your" lot
If your strata plan has these notations, they define the boundaries — full stop. Builders, contractors and renovators assuming "if it looks like part of my lot, it's mine" will get it wrong.
Why Seiwa still matters
The case has been applied repeatedly since 2007 — including in more recent decisions like The Owners – Strata Plan No 87265 v Saaib; Alexandrova [2021] NSWSC, where the Supreme Court confirmed that two separate cubic air spaces of lot property must be divided by a structure that is common property.
It's the foundation case behind every "who's responsible for that?" argument in NSW strata. If a dispute reaches NCAT, the first question the Tribunal asks is what the strata plan says about lot boundaries — and Seiwa is how you answer that.
What this means for your scheme
For owners: before assuming something is "yours" — check the strata plan, including any stratum notations. The face brick wall above your balcony may look like part of your townhouse, but if a notation puts the boundary at the slab line, the wall is common property and the OC maintains it.
For committees: when a repair dispute arises, get the strata plan in front of you before forming a view. Seiwa makes clear the plan is the source of truth.
For everyone: this is why we always recommend a careful read of the strata plan when buying into a scheme — and when planning any work that touches structural elements. The line between lot and common property is rarely intuitive.
Sources
Strata Schemes Development Act 2015 (NSW), s4 (definition of lot and common property).
The Owners – Strata Plan No. 35042 v Seiwa Australia Pty Ltd [2007] NSWCA 272. Full text via NSW Caselaw: caselaw.nsw.gov.au
Later application: The Owners – Strata Plan No 87265 v Saaib; The Owners – Strata Plan No 87265 v Alexandrova [2021] NSWSC.
Bannermans Lawyers commentary referencing this case: bannermans.com.au — The Issue with Planter Boxes