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The Process of Waterproofing a Class 2 Building

Class 2 buildings — apartments and mixed-use residential — are the most heavily regulated waterproofing work in NSW. Under the Design and Building Practitioners Act, the design must be declared by a registered design practitioner, the work must be performed by a registered building practitioner, and the documentation must be lodged on the NSW Planning Portal. Here's the seven-stage process we run for builders and developers.

Stage 1 — Schematic Review

Before architectural documentation is finalised, we review the wet-area and external waterproofing strategy at concept stage. The aim is to lock in fall directions, set-down depths, drainage outlets, and the location of any below-grade tanking before they become expensive to change. A 30-minute schematic review prevents most of the redesign work we see on jobs that come to us late.

Stage 2 — Specification and Detail Drawings

We document the waterproofing strategy in a project-specific waterproofing specification, including:

• Membrane class per AS 4858 (Class I, II or III)
• Nominated systems with current product technical data sheets cross-referenced
• Substrate prep, bond breakers, reinforcing requirements
• Upturn heights — internal per AS 3740, external per AS 4654.2 Table A1 against the project wind class
• Detail drawings: floor wastes, hobs, balcony thresholds, planter boxes, parapets, pipe penetrations

Stage 3 — Design Compliance Declaration (DBPA)

The specification and details are lodged with a Design Compliance Declaration on the NSW Planning Portal. This is the gatekeeper — no work can lawfully commence on a Class 2 project until the declaration is in place. We are registered design practitioners (DEP0001529 — Civil and Structural Engineering) and lodge the declaration directly.

Stage 4 — Pre-Construction Meeting With the Applicator

Before mobilisation, we meet the nominated waterproofing applicator on site, walk through the specification, and confirm they're licensed for the nominated systems. Most contractors carry training certificates for specific manufacturers — verifying the match up-front avoids substitution mid-job.

Stage 5 — Staged Hold-Point Inspections

We inspect at four standard hold points: substrate ready (pre-membrane), bond-breaker and detailing complete, membrane applied (wet film or DFT verification), and final pre-tile/pre-screed. Each hold point is photographed, logged, and signed off — or non-conformances issued for rectification.

Stage 6 — Flood Test and Sign-Off

Once detailing is complete we witness a 24-hour flood test where the geometry allows it. A passed flood test is the strongest evidence the design and execution are sound.

Stage 7 — Final Inspection and Compliance Declaration

At completion we issue a final waterproofing inspection report and, if required, a building compliance declaration for the work. This is the documentation pack the certifier needs to issue an Occupation Certificate — and the documentation the strata committee will look for in five years' time when a leak appears and someone asks "what was actually installed?"

What This Process Avoids

The Class 2 building stock in NSW has a documented waterproofing failure rate — the Shergold-Weir review, the Lambert report, and successive Building Commissioner audits have all identified inadequate design, no third-party verification, and undocumented substitution as the recurring causes. The seven-stage process above is the engineered response to each of those failure modes.