Melbourne's clay soils and high winter water table make basement waterproofing one of the highest-stakes builds a homeowner or developer will commission. Get it wrong and you're chasing the leak for the life of the building. This guide breaks down the three systems we install across Melbourne, what each costs, and where each one is actually appropriate.
System 1 — external tanking (best for new builds)
Applied to the outside of the retaining wall before backfill, external tanking is the gold standard for new basement construction. Typical Melbourne cost is $180–$280/m² of wall area using a bituthene sheet or bentonite system, or $140–$220/m² using a spray-applied liquid membrane. Add $60–$110/m² for a drainage board and geotextile.
This system only works before backfill goes in. Once the earth is against the wall, it is not economically retrievable — you are into internal systems instead.
System 2 — internal cavity drainage (best for existing basements)
A dimpled HDPE membrane is fixed to the internal face of the wall, water is directed to a perimeter channel and pumped out via a sump. Typical Melbourne cost is $220–$340/m² of wall area including the sump and battery-backup pump. This is the pragmatic system for Fitzroy, Carlton and Richmond warehouse conversions where external access is impossible.
System 3 — polyurethane injection (best for discrete leaks)
For a specific crack, cold joint, or tie-bolt penetration, PU or acrylate injection stops the water where it enters. Typical Melbourne cost is $180–$350 per linear metre of crack. Injection is not a whole-basement solution — it fixes discrete water paths.
If you have been quoted injection for a whole-of-wall problem, get a second opinion. It won't hold.
What a compliant Melbourne basement quote should include
Membrane product code and manufacturer. Site assessment report referencing the water table depth. Method statement referencing AS 4654.2. A drainage and pump-out specification if internal. Public liability certificate. A warranty backed by the membrane manufacturer, not just the installer.