What's Included in the Price
- Diagnosis of the moisture source (rising damp, lateral hydrostatic pressure, condensation, or plumbing leak)
- Treatment application: chemical injection ($50–$120 per lineal metre), internal tanking ($70–$100/m2), or external membrane ($120–$200/m2) depending on the diagnosis
- For external work: excavation to foundation walls, membrane application, ag-drain installation, and backfill
- For injection: drilling at 100–150mm intervals, chemical injection of damp-proof course, and hole patching
- Drainage improvements where needed (ag-drain, sump pump at $1,200–$2,500, or subfloor venting)
All below-ground waterproofing work should comply with NCC Part H2 Damp and Weatherproofing requirements, and membrane systems should follow AS 4654.1/4654.2 where applicable. The first step is always proper diagnosis. Treating rising damp when the actual problem is condensation from poor ventilation wastes money. A moisture specialist can test with a moisture meter and carbide kit to determine the source before treatment begins.
What Affects the Cost
- Treatment method. Chemical injection is the least expensive option. Internal cementitious tanking costs more but treats the full wall surface. External membrane with excavation is the most effective approach but also the most expensive and disruptive.
- Area size. One damp wall versus an entire below-grade level produces very different costs. A single wall injection is a day's work; full-perimeter treatment is a multi-day project.
- Water severity. Mild dampness can be managed with negative-side cementitious coatings. Active water flow requires positive-side (external) intervention with membrane and drainage.
- Excavation access. Many Sydney terraces have zero-lot-line boundaries, meaning there is no room to excavate on one or both sides. This limits options to internal treatment, which may require a cavity drain system (dimple board membrane directing water to a sump pump) for heavier moisture loads.
- Sandstone substrate. Sydney's sandstone absorbs and transmits water differently from brick or concrete. Waterproofing systems must be compatible with the stone and not trap moisture inside the masonry, which can cause spalling.
- Structural condition. If prolonged moisture has eroded mortar or caused structural movement, a structural engineer assessment is needed before waterproofing.
Chemical injection on a single wall in an accessible terrace sits toward $500. Full external membrane waterproofing of a below-grade area with excavation on two sides, ag-drain installation, sump pump, and internal tanking on the remaining walls pushes toward $12,000.
Sydney-Specific Considerations
Sydney's topography, geology, and housing stock create specific conditions for below-ground waterproofing.
Sandstone and groundwater in the eastern suburbs. Much of inner Sydney sits on Hawkesbury sandstone, a porous formation that conducts groundwater freely. Properties in Paddington, Potts Point, Surry Hills, and Darlinghurst that are built into hillsides often have rooms or garages extending below the natural ground level. Groundwater migrates through the sandstone and appears as weeping walls, damp patches, or efflorescence (white salt deposits). The treatment depends on the volume: mild dampness may respond to negative-side tanking with a crystalline product like Xypex that bonds into the substrate, while significant water flow requires external waterproofing with a drainage layer. Sydney's variable groundwater levels, which rise and fall with seasonal rainfall and can shift unpredictably through sandstone channels, mean waterproofers need to design for worst-case conditions rather than the level observed on the day of inspection.
Inner-city terraces and zero-lot-line constraints. Sydney's terrace houses in Paddington, Surry Hills, Balmain, Glebe, and Newtown often have below-grade areas used as storage, laundry, or living space. Party walls sit directly on the boundary, making external excavation possible on one side at most, if at all. Internal treatments are often the only feasible option. For heavier moisture intrusion, a cavity drain system using HDPE dimple board (such as Delta MS) fixed to the interior wall creates an air gap that channels water down to a sump pit with a submersible pump. This approach manages the water rather than stopping it at the source, but it works reliably in properties where external access is permanently restricted.
Low-lying suburbs and high water tables. Areas near waterways and low-lying ground, including parts of Alexandria, Mascot, Rockdale, and along the Cook's River corridor, can have water tables that rise after sustained rainfall. Properties in these areas may experience recurring subfloor water that membrane-only solutions cannot address. Ag-drain systems and sump pumps designed for ongoing water management are the appropriate treatment. Where prolonged dampness has caused subfloor timber deterioration, a plumber should check whether a failed stormwater connection is contributing to the problem before waterproofing alone is relied upon.
Strata basements and carparks. In apartment buildings, basement and carpark waterproofing is typically the responsibility of the owners corporation, not individual lot owners. If you are seeing moisture issues in a basement or carpark of an apartment building, raise it with your strata manager. Strata waterproofing remediation is a specialist scope that typically involves negative-side injection, crack sealing, and joint treatment rather than full-membrane replacement.
Hiring a Licensed Waterproofer in NSW
Below-ground waterproofing must be performed by a licensed waterproofer. In NSW, verify licences through NSW Fair Trading. A contractor licence is required for work over $5,000 including GST. You can check licence numbers on the NSW Fair Trading licence search.
A good waterproofer will:
- Provide their current NSW waterproofing licence number upfront
- Conduct a written diagnosis of the moisture source (moisture meter readings, salt analysis) before proposing any treatment
- Specify the treatment system by name (products, methodology, expected outcome)
- Explain warranty terms clearly, including what conditions void the warranty
- Carry public liability insurance
Worth checking:
- A written diagnosis is provided before any treatment is proposed, not just a visual inspection
- The proposed treatment matches the diagnosed problem (chemical injection for rising damp, not for active lateral water flow)
- The waterproofer specifies brand and product names, not just generic descriptions
- Warranty terms include a defined period and state what is covered
- The licence number is current on the NSW Fair Trading register
How We Calculate
Estimates are based on surveyed rates from licensed waterproofers and damp-proofing specialists in the Sydney metropolitan area, adjusted for typical construction and soil conditions in NSW. All prices include GST. Figures cover standard residential basement and subfloor waterproofing. Commercial basement tanking and heritage restoration work may fall outside these ranges.