Waterproofing — Who's Responsible?

Updated 14-10-2026 — this page replaces earlier guidance that said townhouse bathroom membranes were usually the owner's; that was wrong.

Waterproofing is one of the most expensive and most argued-about items in strata. The good news is that the starting rule is simple, and it's the same for townhouses and apartments: the waterproofing in the floor is common property, and the owners corporation has to repair it — unless your strata plan or by-laws say otherwise.

What we're talking about

Waterproofing isn't just one thing. In a townhouse, it includes:

• Membranes — the hidden layer that stops water passing through a slab or floor
• Flashings — strips of metal or rubber where surfaces meet (windows, doors, roof edges)
• Sealants and silicone — around the bath, basin, shower screen and kitchen sink
• Drainage — drains, gullies, falls in the floor
• Wet area waterproofing — under bathroom and laundry tiles

Most waterproofing problems are found after water has already shown up somewhere it shouldn't. Ceilings stain, walls bubble, mould appears, timber rots. By then it's a bigger job than catching it early.

Where your lot ends

Unless your registered strata plan says otherwise, your lot is the space inside your home. It ends at:

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

Everything outside those surfaces is common property. That includes the floor slab, the timber joists and floor sheeting between your two levels, the screed, the waterproof membrane, and the tiles that were laid when the scheme was registered.

This is the same in a townhouse and an apartment, and the same for a ground-floor bathroom and an upstairs one. It doesn't matter whether there's another lot underneath.

Typical position

Grey areas and common disputes

Silicone versus membrane

A lot of bathroom leaks turn out to be failed silicone or sealant, not a failed membrane. Sealant around the bath, basin, shower screen and kitchen sink is the owner's responsibility. Re-siliconing every few years is cheap. Check it first — and if water is still getting through after that, report it.

Who pays to lift and replace the tiles?

To repair a membrane, the tiles on top usually have to come off. Where the OC has to remove finishes to repair common property, the usual approach is that the OC reinstates them to their original standard. If you want an upgrade — better tiles, a different layout — you pay the difference. Get this agreed in writing before work starts.

Renovated bathrooms

Renovating doesn't move the lot boundary. The floor structure under a renovated bathroom is still common property unless the plan says otherwise. What changes is the approval: work on common property needs approval, and an approval must say who maintains the new work. If you, or a previous owner, got approval on the basis that the owner maintains the new waterproofing, that's who maintains it. If the work was never approved and it damaged common property, the OC repairs the damage and can recover the cost from the owner responsible.

Why the strata plan still matters

Don't lift the tiles yourself

It's tempting to get your own tiler in and send the OC the bill. Don't. The Supreme Court has refused to reimburse an owner who repaired common property without approval from the OC or an order from NCAT (Colman [2025] NSWSC 63). Ask first, in writing.

Allow access, and agree the scope

Once the OC is acting, let its contractors in and work with them on a reasonable scope of repair. An owner who refuses reasonable access or a reasonable scope can have any later compensation reduced (Selkirk [2024] NSWSC 760).

If the OC doesn't act

If the OC fails to repair common property, you can claim damages for the loss it causes you — for example, lost rent or repairs inside your lot (s106(5)). You have six years to bring that claim (s106(6)). Talk to us before it gets to that point — most of these are sorted with a clear report and a prompt decision.

Newer buildings

If the building is less than six years old, waterproofing defects may be covered by the builder's statutory warranty under the Home Building Act. Check the completion date before the OC spends its own money.