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AS 4654.2 (membrane design): falls, upstands, laps, terminations

AS 4654.2 sets the design and install rules for external above-ground membranes: 1:100 minimum fall, 150 mm minimum upstand, seam laps, terminations and drainage.

By Dan Waring. Last updated 16 May 2026. Verified 16 May 2026.

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In plain English

AS 4654.2:2012, Waterproofing membranes for external above-ground use, Part 2: Design and installation, is the design-and-install half of the AS 4654 series. It pairs with AS 4654.1 (which sets the product spec). For a builder, AS 4654.2 is the standard the licensed waterproofer is working to on every flat roof, balcony, podium deck, planter, and external above-ground membrane application. NCC 2022 Volume Two Housing Provisions Part H2D8 calls both parts as the DTS pathway for external waterproofing (verified 2026-05-16).

The four numbers a builder should hold in their head when reviewing membrane drawings:

  1. Minimum fall to drains: 1:100 prescriptive (1 mm fall per 100 mm of run).
  2. Minimum upstand height at perimeter walls and doors: 150 mm above finished surface.
  3. Minimum seam lap on sheet membranes: 50 mm (commonly higher per manufacturer’s spec).
  4. Minimum termination chase or termination bar depth: 20 mm (where membrane terminates against a wall and is mechanically capped).

These are AS 4654.2 minimums. Many projects need more (e.g. 1:80 fall on shallow-pond areas, 200 mm upstand at doors in high-exposure climates). The minimums are the floor below which the DTS path does not apply.

What it requires

For the waterproofing designer and installer:

  1. Set falls correctly in the substrate. A flat or back-falling slab cannot be fixed by the membrane alone; the substrate or screed must achieve the design fall before the membrane goes on.
  2. Maintain minimum upstand heights at every termination: against walls, around doors and windows, around drains, around penetrations.
  3. Lap seams to the manufacturer’s spec or the AS 4654.2 minimum, whichever is greater. Seams must shed water; the upper sheet always laps over the lower in the drainage direction.
  4. Drain to designed outlets, sized per the rainfall intensity and the catchment area. Overflow scuppers required where ponding could exceed designed capacity.
  5. Terminate membrane mechanically at perimeter (termination bar with sealant, or chase-cut and re-sealed). Bonded-only terminations fail at 5 to 10 years.
  6. Issue the waterproofing certificate at completion. The certificate names the product, the system, the exposure class, the DFT achieved per AS 4654.1, and the install date.

What it doesn’t cover

  • Product specification. That’s AS 4654.1.
  • Internal wet-area waterproofing. That’s AS 3740:2021.
  • Below-grade tanking. That’s AS 4858.
  • Roof structure design. That’s AS 1170 (loads), AS 1684 (timber) or AS 4100 (steel) for the substrate carrying the membrane.
  • Floor coverings or top finishes over the membrane. Tile, screed, pebble or paver overlays sit under separate standards (AS 3958 for tiling, etc.). AS 4654.2 stops at the membrane surface.

Practical implications

  • 1:100 fall is the most-litigated detail in residential membrane defects. A balcony or flat roof set “flat enough” by the slab crew, then puddled by the screed, has no AS 4654.2 fall. The membrane is then defective by design regardless of how well the waterproofer applies it. Set falls in the substrate first.
  • 150 mm upstand at doors traps builders. External-door thresholds set flush with the finished floor inside the building cannot achieve 150 mm membrane upstand without raising the door sill or adding a step. The fix is at the architectural-design stage, not at the waterproofer’s install. Catch this at CC application.
  • Penetration sealing is the failure point at 5-10 years. Around drains, plumbing penetrations, and balustrade fixings, the membrane termination needs to be detailed exactly as the manufacturer specifies or worse than the AS 4654.2 minimum. Cutting around a balustrade bolt with a knife and squirting silicone is a defect.
  • Termination bars must be UV-stable. Painted-aluminium bars in a high-sun position degrade. Stainless steel or anodised aluminium is the durable choice.
  • Membrane sample tests at completion are a useful insurance. On critical-exposure projects (Cat III), pull a 50 mm sample after cure for a third-party tensile and adhesion test. The cost is small; the evidence supports a defect claim later.

References

See also

Last updated: 2026-05-16. Verified: 2026-05-16. Quarterly review for currency.

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