Below ground, beyond the Code

Somewhere right now, on a project that has already gone to tender, there is a drawing note that says "waterproofing to manufacturer's details and NCC." That note has launched a hundred leaks.

Here is the uncomfortable arithmetic of NCC Volume One. For external above-ground waterproofing, the Deemed-to-Satisfy pathway points you at AS 4654 and you can, with care, tick your way to compliance. For below-ground waterproofing, there is no current DtS pathway and the recent NCC framework has not provided one. Where below-ground waterproofing is required to demonstrate NCC compliance, it has to be justified as a Performance Solution.

In practice, plenty of projects never noticed. The 'performance solution' was a membrane brochure stapled to optimism, signed off in the race to construction certificate. The water noticed. Water always notices. It then spends the next decade demonstrating its findings, hanging stalactites from the carpark soffit and dripping lime-laden water onto the shiny new cars parked below, where it can leave its mark, etched into the duco.

NCC 2025 closes the loophole of not paying attention. Published in May 2026, it rebuilds Section F's water provisions from the slab up. The old Parts F1 and F3 are merged. "Water" is now a defined term that captures sub-surface water and ground moisture, not just rain doing the obvious thing. That change matters because the ABCB's own research found most water-related defects come from below finished surfaces, through tiles, pavers, screeds and tired membranes, rather than from rain hitting the roof.

For concrete balconies, podiums and roofs over habitable space, there are new Deemed-to-Satisfy provisions covering falls, drainage and where the membrane sits in the build-up. Falls must now be designed into the structural slab, with an allowance for ten years of concrete deflection, so the drainage still works once the slab has finished its long, slow sag. The old exemptions for warehouses and factories are gone too.

Adoption is a patchwork. Victoria, the ACT and WA are transitioning now. NSW and Queensland have deferred to May 2027, with NSW flagging flexibility for apartment remedial work to use either edition's waterproofing provisions. So for the next year or so, the answer to "which code applies to my building?" is "it depends," which is nobody's favourite answer but very much mine to help with.

What does not change between editions is this: a Performance Solution is an engineering argument, not an administrative formality. It has to demonstrate, with evidence, how water will be collected, drained and excluded for the life of the building. Written properly, it is often a better outcome than DTS, because it is designed for your building rather than a generic one. Written badly, it is a leak with a cover sheet.

The same logic applies to peer review. An independent set of eyes across the waterproofing design before the concrete is poured costs a rounding error against remedial work after settlement. The cheapest waterproofing defect to fix remains the one fixed in CAD.

Watershed Projects writes Performance Solutions and provides independent waterproofing design peer reviews for NCC Volume One buildings. If your next project includes a basement, podium or balcony, which is to say all of them, it is worth a conversation well before the formwork goes up.