Waterproofing Membranes Are Common Property — Even When They're Inside Your Lot

If water is coming through your balcony, courtyard or planter box, here's the principle to remember: the waterproofing membrane underneath is almost always common property — and that means it's the owners corporation's job to fix, not yours. Even if everything sitting on top of it is technically your lot.

What's a membrane and why does it matter?

A waterproofing membrane is the layer that stops water getting through a slab into whatever's underneath. You don't usually see it because it sits under your tiles, pavers, soil or screed.

You'll find membranes:

• Under balcony tiles or paving
• Under planter boxes and raised gardens
• Under courtyard paving and outdoor entertaining areas
• Inside retaining walls
• Beneath flat roof finishes
• Under bathroom and laundry floor finishes

When membranes fail — and they all do eventually — water finds its way through, and that's when ceilings stain, walls bubble, mould appears, and timber starts to rot.

The legal position — they're common property

The leading commentary on this comes from Bannermans Lawyers, who put it plainly in their 2023 article on water ingress disputes:

And on planter boxes specifically (Bannermans, November 2022):

The reasoning is that membranes are part of the building's structural fabric. They protect the slab — which is common property — and they're integral to keeping the whole building waterproof. They aren't your fixtures and fittings; they're part of the structure.

So who pays?

If the membrane has failed, the owners corporation has a strict duty under Section 106 of the Strata Schemes Management Act 2015 to repair and maintain it. "Strict" means there's no "we'll get around to it" defence — if it's common property and it's broken, the OC must fix it.

The challenge is that fixing a membrane usually means lifting whatever's on top of it (your tiles, your paving, your soil). Those finishes are lot property. So the OC fixes the membrane; the lot owner is responsible for replacing the finishes — unless those finishes were damaged by the membrane failure itself, in which case the OC may have to cover the cost as part of putting things right.

What about replacing external waterproofing?

One important practical point: replacing an external waterproofing membrane above ground level is not exempt development in NSW. Bannermans Lawyers (October 2024) explains the reasons in detail, but the short version is:

• The SEPP (Exempt and Complying Development Codes) 2008 only applies if the building has a current fire safety statement (cl 1.16(2), Part 2 Div 1).
• Many older schemes don't have current fire safety statements — pre-1988 buildings under Part 59 of Ordinance 70 weren't required to lodge them.
• Even if eligible, the works must comply with AS 4654.1 and AS 4654.2 — and many existing buildings won't comply (inadequate drainage, wrong step-down height, no fall in the substrate, etc.).

That means an external membrane re-do usually needs proper planning approval, not just a contractor turning up and starting work. Getting it wrong can mean stop-work orders, contractor termination, and insurance exclusions.

What to do if you've got a leak

1. Document it. Photos with dates, water stains, any expert reports.
2. Report it in writing to the strata manager. Email is fine — you want a record.
3. Don't start fixing it yourself. If the issue is the membrane, work on top of it (lifting tiles, pulling out plants) might be necessary but it should be coordinated with the OC's repair.
4. Expect an expert to be called. Most membrane disputes need a building consultant or waterproofing specialist to identify the actual source.
5. If the OC drags its feet, mediation through NSW Fair Trading or an application to NCAT is available — and damages for losses you've suffered can be recovered. See our article on Section 106(5) damages claims.