Common Property vs Lot Property: Who's Responsible for What?

Almost every maintenance argument in a strata scheme comes down to one question: is this the owners corporation's problem, or the lot owner's? A cracked ceiling, a leaking shower, a rotten window frame, a balcony tile lifting in the sun — someone has to pay, and the answer is never "whoever complains loudest". It's decided by a boundary line drawn on a plan that was registered when the building was subdivided, sometimes decades ago, and adjusted by a regulation and any by-laws your scheme has made since. Get the boundary right and the repair conversation is short. Get it wrong and you either spend the scheme's money fixing something an owner should have paid for, or you leave an owner stranded with a bill that was never theirs. This guide sets out where the line usually falls, how to find it on your own plan, and how to settle the grey areas before they become a fight.

The one idea that decides everything: the boundary

A strata scheme is legally two kinds of property sitting inside the same building. There's lot property — the individual units that owners buy, sell, and mortgage — and there's common property — everything else, owned collectively by all the owners through the owners corporation (called the body corporate or strata company in some states). The boundary between them is what matters, because the general rule across Australia is simple:

The owners corporation maintains and repairs the common property. Each owner maintains and repairs their own lot.

So the entire question of "who pays" collapses into "which side of the boundary is the thing that broke?" Everything else — insurance, repair bills, whose contractor turns up — follows from that one line.

Why it matters

• It decides who pays. A repair on the common property side comes out of the scheme's funds (levies); a repair on the lot side is the owner's own cost. The boundary is the difference between a levy expense and a personal one.
• It decides who can act. An owner can't unilaterally alter common property, and the owners corporation can't enter and renovate someone's lot. Knowing the boundary tells you who's even allowed to do the work.
• It's where disputes start. Water leaks, balcony repairs, and window failures are the most common strata disputes precisely because they sit near the boundary. Settling the line early is the cheapest dispute-prevention there is.

Where the boundary usually falls

In most schemes — particularly the stacked, apartment-style buildings where lots sit above and beside each other — the registered plan defines each lot by its internal surfaces. The boundary runs along:

• the upper surface of the floor,
• the under surface of the ceiling, and
• the inner surface of the boundary walls.

Picture the lot as the cubic airspace inside those surfaces, plus the non-structural things within it. On that model, the structure itself — the external walls, the roof, the slab and foundations, the load-bearing internal walls, the main structural beams — is common property, even though part of it (the inner face of your living-room wall) is what you paint and live against. The paint, the plaster skin, the floor coverings, the internal fit-out: lot. The structure holding it all up: common.

That's the default, and it's why so many owners are surprised to learn the wall they think of as "theirs" is structurally the scheme's responsibility. But it is only the default. The registered plan governs, and plans can and do draw the boundary differently — some define lots by a structural centre-line, some by external faces, and freestanding "standard-format" schemes (villas and townhouses on their own patch of land) often put the whole building on the lot side. Never assume; check the plan.

Reading it off your own plan

You don't guess the boundary — you look it up. Three documents, in order:

1. The registered strata / survey / community plan. This is the authoritative source. It shows the lot boundaries and usually carries a notation about whether boundaries are the internal face of walls, a structural line, or something else. If you can't find your copy, it's obtainable from your state's land titles registry.
2. The state regulation. Every jurisdiction has a schedule or set of provisions that fills in the detail the plan doesn't — most importantly, how services (pipes, cables, ducts) are split, which is almost always by who they serve (more on that below).
3. Your scheme's by-laws. By-laws can shift maintenance responsibility for specific items — a common example is a by-law making owners responsible for the windows or the exclusive-use courtyard attached to their lot. A by-law can change who maintains something even where the structure remains common property.

Work through those three and the boundary for almost any component becomes answerable.

The grey areas, and how to think about them

The boundary line is clean in theory and messy at exactly the points people argue about. Here's how each classic flashpoint usually resolves — always subject to your plan, regulation, and by-laws.

Windows and glass

The frame and the surrounding structure sit in the external (boundary) wall, so the structural window assembly is typically common property. But the split between "the owners corporation fixes the frame and the seal" and "the owner cleans the glass, oils the hinges, and replaces a pane they cracked" is one of the most commonly modified items — many schemes have a by-law handing routine window and glass maintenance to owners. Check for one before you assume.

Doors

The front/entry door in a boundary wall is usually common property (it's part of the fire-separating structure and the building's appearance); its lock and internal handle are often the owner's. Internal doors wholly inside the lot are the owner's. A screen door or security door an owner has added is theirs — and may have needed approval as an alteration.

Floors, tiles, and floor coverings

The structural floor slab is common property. What sits on top of it — carpet, floorboards, tiles, the finished surface — is generally lot property. The exception that causes grief is waterproofing membrane in bathrooms and on balconies: it's often below the finished surface and physically part of the structure, and responsibility for it varies. Treat any wet-area waterproofing question as one to resolve against the plan and regulation specifically, because it's both expensive and ambiguous.

Balconies and courtyards

A balcony is a genuine hybrid. The structural slab, balustrade, and any waterproofing are typically common property; the tiles or decking surface an owner can be responsible for; and where the balcony or courtyard is exclusive-use common property, a by-law frequently shifts some or all of the upkeep onto the owner who enjoys it. Establish which parts are structure, which are finish, and whether an exclusive-use by-law applies.

Pipes, wiring, and services

This is the one area with a reliable rule of thumb: services are split by who they serve. A pipe, drain, cable, or duct that serves more than one lot (or the common property) is common property; one that serves only a single lot is generally that lot owner's responsibility — even where it runs through a common wall or floor to get there. So the shared stormwater stack is the scheme's; the branch line from it into unit 4 only is unit 4's. This is why a leak's cause matters as much as its location — see below.

Ceilings and the space between floors

The inter-floor space — the void between the ceiling of the lower lot and the floor of the upper lot, where pipes and wiring run — is normally common property, even though it's sandwiched between two lots. That surprises owners on both sides of the slab, and it's exactly where cross-lot leaks live.

Water leaks: the boundary's hardest case

Water leaks deserve their own note because they're the most litigated repair in strata and they don't respect the boundary neatly. A leak appears in one lot but originates somewhere else — the flat above, a common stack, a failed common-property membrane. The rule to hold onto: responsibility follows the source, not the symptom. If the water comes from common property (a corroded common pipe, failed balcony waterproofing on common structure), it's the owners corporation's to fix and, often, to make good the damage. If it comes from a single lot's own pipe or the owner's own renovation, it's theirs. Because pinning down the source is the whole game, the sequence is: stop the water, then investigate the cause (a plumber or building consultant, paid for by whoever is provisionally responsible or split until the source is known), then allocate the repair. Fixing the visible damage before you've found the source just guarantees you'll be doing it again.

Per-state specifics

The boundary principle is national, but the default line and the fine print are set by each state's strata legislation and regulation. Check the callout for your scheme.

When the boundary genuinely isn't clear

Sometimes the plan is old, the notation is ambiguous, or the component straddles the line. Before it turns into a standoff:

1. Get the plan and the regulation in front of you — the answer is right more often than committees expect once they actually read the boundary notation.
2. Check for a by-law that reassigns the item; scheme by-laws override the default for the things they cover.
3. If it's still unclear, get a written opinion — a strata lawyer or an experienced strata manager can advise on a genuinely borderline component for a modest fee, which is far cheaper than a tribunal case or a wrong repair.
4. Record the decision. Once you've settled who's responsible for a recurring grey area (the windows, the balconies), minute it or make a by-law so the next committee doesn't re-fight it.

Never let a "we'll sort it out later" leak or crack sit because the boundary is unclear — the ambiguity is about who pays, not whether it gets fixed. Fix it, then allocate the cost.

Common mistakes

1. Assuming "inside my unit" means "my responsibility"

Plenty of things physically inside a lot — the structural wall, a common pipe passing through, the inter-floor void — are common property. Location isn't the test; the boundary on the plan is.

2. Treating a leak's location as its cause

Water shows up where gravity takes it, not where it started. Allocating the repair to the lot where the stain appears, without tracing the source, is how schemes pay for the wrong thing and end up doing it twice.

3. Ignoring the by-laws

A scheme can have a by-law that hands window, balcony, or exclusive-use maintenance to owners. Committees that reason only from the "default" boundary and never check their own by-laws get it wrong for exactly those items.

4. Letting the owners corporation quietly fund lot repairs

Fixing an owner's own pipe or fit-out from levies feels neighbourly but spends everyone's money on one lot, and sets a precedent. If it's on the lot side, it's the owner's — bill it there.

Frequently asked questions

How do I actually find out where my lot ends?

Start with the registered strata/survey plan — it defines the boundaries and usually notes whether they run along internal wall surfaces or a structural line. Then check the state regulation (for how services are split) and your scheme's by-laws (which can reassign specific items). Those three together answer almost any component.

Who pays to fix a leaking shower or balcony?

It depends on which part failed. The structural slab and waterproofing membrane are commonly the owners corporation's; the finished tiles or surface are often the lot owner's. Because wet-area waterproofing sits right on the boundary, resolve it against the plan and regulation specifically rather than assuming — and trace where the water is actually coming from first.

The pipe that burst runs through a common wall — is it common property?

Not necessarily. Services are usually split by who they serve: a pipe serving only one lot is generally that owner's, even where it runs through common structure to reach the lot; a pipe serving multiple lots or the common property is the scheme's. Where it physically sits matters less than what it feeds.

Can we change who's responsible for something like windows?

Yes — that's what by-laws are for. A scheme can make a by-law allocating maintenance of a specific item (windows, an exclusive-use courtyard, a private balcony) to the benefiting owner, even where the structure remains common property. It has to be made properly at a general meeting and registered where your state requires.

An owner won't fix something on their side of the boundary — what can we do?

If it's genuinely lot property, the owners corporation can't do the work itself, but where the owner's neglect affects common property or other lots (a leak into the flat below, say), most states let the scheme issue a notice to comply and, if ignored, escalate to the tribunal. Document the request and the impact.

Quick checklist

• [ ] You have a copy of the registered strata/survey plan and have read its boundary notation
• [ ] You know whether your lots are bounded by internal surfaces, a structural line, or (for freestanding schemes) include the building
• [ ] You've checked the state regulation for how pipes, cables, and services are split (usually by who they serve)
• [ ] You've checked the scheme's by-laws for any item whose maintenance has been reassigned to owners
• [ ] For any leak, you trace the source before allocating the repair
• [ ] Recurring grey areas (windows, balconies, exclusive-use areas) are settled in writing so they're not re-argued
• [ ] Common-property repairs are funded from the scheme; lot repairs are billed to the owner

Related resources

• Strata Insurance Explained: What Your Scheme Must Cover, and What It Doesn't
• Admin Fund vs Capital Works Fund: What Can You Legally Spend From Each?
• What "Self-Managed Strata" Actually Means (and When It's the Right Call)

This guide is general information for self-managed strata schemes in Australia. It is not legal advice. Lot and common property boundaries are set by your scheme's registered plan and vary between states and between individual schemes — always check the plan, the strata legislation and regulation that apply to your scheme, and your by-laws, and seek professional advice on genuinely borderline components.