What AS 4654.2 requires for balcony waterproofing — falls, upturns, thresholds and drainage — and what it means when an existing NSW strata balcony doesn't comply.
Every balcony defect report in NSW eventually names the same document: AS 4654.2. It gets quoted at owners corporations as if it settles the argument — the balcony doesn’t comply, so it has to be rebuilt.
Sometimes that’s right. Often it’s more complicated, because AS 4654.2 is a design and installation standard written for new work. Your building is not new work. Understanding the difference is what separates a $40k balcony program from a $400k one.
This guide sets out what the standard actually requires, what it means when an existing balcony doesn’t meet it, and the decisions a strata committee has to make in between. It covers the same ground we walk through on balcony repairs and remediation projects across Sydney.
AS 4654.2-2012 is the Australian Standard for waterproofing membranes used externally above ground — roofs, decks, balconies and planter boxes. It is referenced in the National Construction Code as a Deemed-to-Satisfy pathway (F1D4 and F1D5 in Volume One, H2D8 in Volume Two). If a balcony was built to the Code, it was meant to be built to this standard.
It applies to your building in two ways. For original construction, it sets the benchmark an engineer will measure the existing balcony against. For remedial work, it sets what the new system has to achieve once you open the balcony up — and that is where the cost sits.
A trafficable balcony needs a minimum fall of 1:100 to the drainage outlet — 10mm of drop over a metre. Newer Code provisions push the substrate fall to 1:80 to allow for build-up tolerance, so confirm the current requirement with your certifier before design. Ponding water on a finished balcony is the clearest sign fall was never achieved.
This single number causes more remedial cost than any other clause. A balcony built flat cannot be brought to 1:100 by recoating it. You either lift the tiles and lay a new screed to fall, or you lift the tiles, grind the slab and lay a new screed to fall — and if the slab has already lost cover, you’re into rebuilding a failed waterproofing system over repaired concrete rather than a tidy re-tile.
The membrane must turn up vertically against adjoining walls and terminate above the finished surface — commonly 100mm to 150mm, though required termination heights range from roughly 40mm to 180mm depending on the building’s wind classification and how the door threshold is detailed.
This is the detail most often missed on older balconies, because the upturn is hidden behind render or cladding. It is also the reason a leaking balcony is rarely just the balcony — water that gets behind a short upturn tracks into the wall cavity and shows up in the apartment below, two rooms away from the actual failure.
The balcony surface must be set down below the internal floor so water cannot run inside — commonly at least 50mm, with the membrane dressed into and under the door frame. Where a level threshold is required for accessibility, the standard expects a compensating drainage design, such as a grate directly at the door.
Thresholds are the hardest thing to fix retrospectively. You cannot lower a balcony slab, so achieving set-down on an existing building usually means removing the tile and screed build-up entirely, or accepting a designed drainage solution at the door instead. Expect this to be the item your engineer and your builder argue about.
The standard requires outlets sized and located so the balcony drains completely, plus overflow provision so a blocked outlet cannot pond water above the membrane upturn. One outlet in one corner, with no overflow, is a design failure regardless of how good the membrane is.
On strata buildings we routinely find outlets set above the finished screed level — the drain is physically higher than the water it is meant to collect. No membrane fixes that.
Not retrospectively, as a general rule — a balcony built to the code of its day is not automatically unlawful now. But once you carry out remedial work, the new work is expected to meet the current standard, and your certifier, engineer and insurer will all assess it on that basis.
This is the point most committees miss. The question is not “does our balcony comply?” It is “what will we be required to build when we touch it?” That answer drives the budget, and it is why partial patch repairs so often turn into full replacement scopes mid-project.
| What the balcony fails on | Typical remedial response | Cost driver |
| Membrane worn or punctured, falls OK | Strip tiles, new membrane, re-tile | Lowest — finishes only |
| Insufficient fall / ponding | Strip to slab, new screed to fall, new membrane | Screed volume + build-up height |
| Short or missing wall upturn | Open adjoining wall finish, dress upturn, reinstate render or cladding | Facade make-good, access |
| Threshold set-down not achieved | Remove build-up or design drainage at door | Often needs engineer sign-off |
| Concrete spalling under the membrane | Concrete repair first, then full system | Structural repair + extended program |
We deliberately avoid a per-square-metre figure here, because the range is set by which of these five you’re actually dealing with, not by membrane price. For indicative bands, see what balcony waterproofing costs in Sydney.
On a Class 2 building, responsibility sits with the owners corporation for common property, discharged through a designer or engineer who specifies the system and a registered practitioner who builds it. Under the Design and Building Practitioners Act, waterproofing is a regulated design — the design must be declared, and the builder must build to it.
That has a practical consequence: your contractor cannot lawfully “work it out on site”. If the scope you’ve been given doesn’t resolve fall, upturn and threshold before work starts, you don’t have a scope — you have a variation waiting to happen. The Atomic Projects remedial building team treats those three items as the first conversation on every balcony job, not the last.
On a recent Class 2 program in St Leonards, the engineer’s report called for membrane replacement on 40 balconies. Invasive investigation on the first four found the screed had been laid dead flat and the outlets sat proud of the finished level. Re-membraning would have produced 40 compliant membranes over 40 non-compliant balconies, and the same leaks two years later.
The scope changed to full strip-out and re-screed on the affected stacks. More expensive on day one, and the only version that would have survived a defects claim. That sequencing logic is the same one we apply to re-waterproofing a balcony in a Class 2 apartment block generally: diagnose the substrate before pricing the membrane.
Atomic Projects is a Class 2 DBP Registered Building Practitioner and has delivered $20M+ of remedial work across 100+ Sydney strata buildings, from $50k balcony repairs to $5M+ facade programs.
If you’ve been handed a balcony report and can’t tell whether you’re looking at a membrane job or a rebuild, we’ll assess it and tell you which — get a free assessment.
Send photos, the engineer's report, or just the symptoms — whatever you've got. A registered builder reads it and calls you back. No call centre, no obligation.