Reviewed and updated 14-10-2026. We corrected how lot boundaries work. By default the boundary is the inner surface of the walls and the upper surface of the floor (not the centre line of shared walls), and the Seiwa case applied that default because the plan was silent — it was not a case about stratum notations. Floor structure and membranes, including in bathrooms, are common property by default. We also removed a case we could not verify.
"That's not my problem — that's the owners corporation's." It's one of the most common questions in strata, and the answer matters because it decides who pays. Here's the plain-English guide for townhouse and villa owners.
The starting point — Section 106 of the Act
Under section 106 of the Strata Schemes Management Act 2015 (NSW), the owners corporation has a strict duty to maintain and repair the common property. "Strict" means there's no "we did our best" or "we didn't have the money" defence — if it's common property and it's broken, the owners corporation must fix it.
So the whole question is working out where your lot ends and common property begins.
How the line is drawn
Lot boundaries are set by section 6 of the Strata Schemes Development Act 2015 (NSW). Where the strata plan doesn't describe a boundary, the default rules are:
- Walls: the boundary is the inner surface of the wall (s6(1)(a)(i)). The paint and plaster face inside your home are in your lot; the wall structure is common property.
- Floors: the boundary is the upper surface of the floor (s6(1)(a)(ii)). The slab, floor structure, screed and membrane are common property.
- Ceilings: the boundary is the under surface of the ceiling (s6(1)(a)(ii)). The roof space and roof are outside the lot.
- Anything else: only as described on the registered floor plan (s6(1)(b)).
These defaults are the same for townhouses and apartments. What can make a townhouse different is a notation on its registered plan — for example, one saying the lot includes the building structure. Many townhouse plans have notations like that, so always read your plan. For plans registered before 2015, the same default rule was in section 5(2) of the Strata Schemes (Freehold Development) Act 1973.
In The Owners – Strata Plan No 35042 v Seiwa Australia Pty Ltd [2007] NSWCA 272, the NSW Court of Appeal applied the default floor rule where the plan was silent and held that the tiles laid before registration, and the membrane under them, were common property. The boundary is fixed at registration and doesn't move when an owner later renovates ([39]).
Townhouse quick reference — where the plan is silent
This table shows the default position. A notation on your plan or a registered by-law can change any of it.
| Item | Default |
|---|---|
| Walls between townhouses (structure) | Owners Corp |
| External walls (face brick, render, cladding) | Owners Corp |
| Roof, roof structure and gutters | Owners Corp |
| Slab, floor structure, screed and waterproofing membranes — including bathrooms, ground floor and first floor | Owners Corp |
| Floor tiles laid before the plan was registered | Owners Corp |
| Windows and external doors set in the wall structure | Owners Corp |
| Pipes and wiring inside the wall or floor structure | Owners Corp |
| Driveways, paths, fencing and landscaping in common areas | Owners Corp |
| Paint and plaster face inside your home | Lot Owner |
| Your own appliances, furniture and contents | Lot Owner |
| Garage / carport | Check your plan |
| Private courtyard / fenced garden | Check your plan |
| Hot water systems | Check your plan |
| Anything covered by a common property rights by-law | Check the by-law |
The "check your plan" items vary. Some strata plans include garages and courtyards in the lot; others leave them as common property with an exclusive use by-law. An exclusive-use area is still common property.
The membrane trap
This is the one that catches people out. Even when something looks like it's part of your home, the waterproofing membrane beneath it is common property by default. So if your bathroom floor is leaking into the room below, or your balcony tiles have lifted because the membrane has failed, that's the owners corporation's job unless your plan or a registered by-law says otherwise. More detail in our article on waterproofing membranes.
Exclusive-use areas and by-laws
A common property rights by-law (made under section 143, with the benefiting owner's written consent, and registered) can make an owner responsible for keeping an area in good repair. NCAT's Appeal Panel held that a by-law like this shifted the cost of repairing an exclusive-use terrace, including its roof, to the owner (Sorbara v The Owners – Strata Plan 75666 [2021] NSWCATAP 369). An ordinary by-law that isn't a common property rights by-law can't do this.
What if you and the owners corporation disagree?
- Put your concern in writing, with photos and any expert report.
- Mediation through NSW Fair Trading is often worth trying before a tribunal application.
- NCAT can make orders requiring the owners corporation to carry out repairs, and can award damages under section 106(5) for losses caused by a failure to repair. There is no monetary ceiling on those awards — see our article on damages claims when the owners corporation fails to repair.
What this means for your scheme
The biggest mistake we see is owners fixing common property themselves — usually a waterproofing membrane — and then finding they can't recover the cost because the work wasn't approved first.
If you're not sure: ask. We'd much rather have a 10-minute phone call, and a look at your strata plan, before something is started than work out responsibility after a contractor has been on site for three days.
Sources
Strata Schemes Development Act 2015 (NSW), s4 (common property is any part of the parcel not comprised in a lot) and s6 (lot boundaries).
Strata Schemes Management Act 2015 (NSW), s106, s143.
The Owners – Strata Plan No 35042 v Seiwa Australia Pty Ltd [2007] NSWCA 272. Sorbara v The Owners – Strata Plan 75666 [2021] NSWCATAP 369. Full texts via NSW Caselaw: caselaw.nsw.gov.au