● Building code
Basement waterproofing standard. There is not one.
·1 min read·FORSPEC Technical Team
The short version
- AS 4654.1 and AS 4654.2 cover external waterproofing above ground. They do not cover basements.
- No Australian Standard covers below-ground membranes or tanking.
- A new international guide, ISO/TS 18734:2026, helps choose a barrier. It is guidance only.
Specifications for basements often say the membrane is to comply with AS 4654.2. It cannot. That standard's scope ends at the ground.
What exists
- AS 4654.1 and AS 4654.2
- External, above ground. Not basements, not pools.
- AS 3735
- The engineer's standard for concrete that holds liquid: tanks and reservoirs
- ISO/TS 18734:2026
- International guidance for barriers on underground concrete. Not adopted in Australia, not called up by the NCC.
What the new guide asks you to decide
- How it is built. Is the membrane laid before the concrete (pre-applied) or after (post-applied)?
- What is in the ground. Water table, water pressure and anything aggressive in the soil.
- How dry the space must be. A car park and an archive room are not the same job.
What to specify to
- The membrane's own test evidence. A below-ground sheet can still be tested and classed to AS 4654.1 as a material.
- The manufacturer's system: sheet or coating, waterstops in every joint, and the pile head and penetration details.
- A drawn detail for every junction, agreed before the pour.
Where this comes from
- AS 4654.2-2012: 1.1
- ISO/TS 18734:2026: 4 to 8
- AS 3735-2001: Scope
Standards are summarised in FORSPEC's own words as a guide. Read the standard itself and your project documents before you build.
Systems, products and drawings
SystemBelow-Ground Waterproofing & Basement TankingThe full build-up, layer by layer→SystemNegative-Side WaterproofingThe full build-up, layer by layer→ProductPREFLEX 3000Pre-applied HDPE membrane laid before the pour, so water cannot migrate laterally between membrane and concrete.→ProductACTFLEX 5000Self-adhesive sheet membrane with cross-laminated HDPE reinforcement for basements, retaining walls and planter boxes.→ProductACTFLEX 988 CWPTwo-part cementitious acrylic membrane for basements, tanks and pools that applies to damp cured concrete, normally without primer.→DrawingBGL001 · Retaining Wall System1CAD detail: PDF and DXF→DrawingBGL011 · Lift Pit Base to Strip Footing CJCAD detail: PDF and DXF→DrawingCJS002 · Cast In Internal ConstructionCAD detail: PDF and DXF→RangeAll FORSPEC productsBy system, with data sheets and calculators→
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