Protecting Auckland's basements, retaining walls, lift pits and underground structures from groundwater and hydrostatic pressure. NZ Building Code compliant. Licensed Building Practitioner #BP181755.
Tanking is the application of a waterproof membrane system to below-ground structures — basements, retaining walls, lift pits, underground car parks and any building element that sits below the natural ground level. Its purpose is to create a continuous waterproof barrier that prevents groundwater, soil moisture and hydrostatic pressure from penetrating the structure.
In Auckland, tanking is particularly critical due to the region's high annual rainfall (1,200mm+), clay-heavy soils that retain moisture, and rising water tables in many suburbs. Without effective tanking, below-ground spaces are susceptible to dampness, mould, structural deterioration and in severe cases, flooding during heavy rainfall events.
The New Zealand Building Code (Clause E2 — External Moisture) mandates that all building elements in contact with the ground must be protected from moisture ingress. For habitable basements and living spaces below ground level, a tanking membrane system is not optional — it is a legal requirement. As a Licensed Building Practitioner, we ensure every tanking installation meets or exceeds these code requirements.
Tanking is essential for any structure with below-ground elements exposed to soil moisture or groundwater
Any habitable space below ground level requires tanking to prevent moisture penetration through walls and floors. This includes home offices, media rooms, bedrooms, and storage areas in basement conversions.
Earth-retaining walls that have living spaces, garages or storage behind them must be tanked on the earth-facing side to prevent water from migrating through the concrete or masonry into the building.
Concrete floor slabs that sit at or below the water table level need tanking to prevent hydrostatic pressure from forcing groundwater up through the concrete and into the building.
Commercial and residential underground parking structures require comprehensive tanking systems to manage groundwater ingress, protect the structural reinforcement from corrosion, and maintain safe, dry conditions.
Lift pits and below-ground service ducts are particularly vulnerable to water ingress and require specialist tanking to protect critical electrical and mechanical equipment from moisture damage.
Built-in planter boxes and garden beds on structures need tanking to prevent irrigated water and soil moisture from migrating into the building elements below or adjacent to them.
We select the tanking membrane system based on each project's specific requirements — the depth below ground, groundwater levels, soil type, access conditions and whether the application is external (positive-side) or internal (negative-side). All systems we use are BRANZ-appraised and compliant with the NZ Building Code.
Our most commonly used external tanking system. Modified bitumen sheets are torch-applied to the external face of retaining walls and basement walls, providing a robust, self-healing waterproof layer that resists root penetration and chemical attack from soil.
Ideal for complex geometries, pipe penetrations and irregular surfaces where sheet membranes are difficult to detail. The liquid membrane conforms to any shape and cures to form a seamless, fully bonded waterproof coating.
Self-adhesive or mechanically fixed sheet membranes for large, flat retaining wall applications. These systems provide consistent thickness and reliable performance across extensive areas.
A critical component of any tanking system. Protection boards shield the membrane from backfill damage, while drainage boards channel groundwater away from the structure to reduce hydrostatic pressure on the membrane.
Below-ground waterproofing is one of the most critical elements in any building project. The NZ Building Code sets strict requirements for tanking that must be met to obtain a Code Compliance Certificate.
Building elements in contact with the ground must prevent moisture from entering the building
Tanking systems must achieve minimum 50-year durability for primary structure protection
Effective drainage must be integrated to manage groundwater and surface water around below-ground structures
LBP #BP181755 with Roofing R4 & R5 endorsements. Tanking membrane installation is restricted building work under the Building Act 2004 and must be carried out by a licensed practitioner.
We exclusively use BRANZ-appraised tanking membrane systems that have been independently tested and verified for performance in New Zealand conditions.
Tanking membrane costs vary significantly depending on the scope of work, access conditions, system selected and the level of groundwater pressure the membrane needs to resist. Typical pricing ranges include:
Retaining Wall Tanking
$80 – $120/m²
Basement External Tanking
$100 – $150/m²
Below-Slab Membrane
$90 – $130/m²
Remedial Internal Tanking
$120 – $180/m²
These are indicative ranges only. Every tanking project is unique and we provide detailed quotes based on an on-site assessment of the specific conditions and requirements.
Trusted by homeowners and builders across Auckland — here is what they say about our work
"Your Subbie did an excellent job with our TPO roof installation. Professional, on time, and the quality is outstanding. We had tried two other companies before and neither could solve our recurring leaks — Matt fixed it first go."
Sarah Thompson
Devonport, Auckland
January 2026
"Matt and his team transformed our leaking deck with their Dec-K-Ing system. No more water damage, and it looks fantastic. Great communication throughout the whole project."
Mike Johnson
Grey Lynn, Auckland
February 2026
"We regularly use Your Subbie for waterproofing on our projects. Their expertise with Butynol and torch-on systems is top-notch — reliable, clean work every time."
David Lee
Remuera, Auckland
March 2026
Tanking is the process of applying a waterproof membrane to below-ground structures to prevent water ingress from surrounding soil and groundwater. It is required for any habitable basement, underground car park, retaining wall with living spaces behind it, lift pits, and below-slab areas where hydrostatic pressure from groundwater could force water through the concrete.
We use BRANZ-appraised tanking membrane systems that comply with the New Zealand Building Code. Our primary systems include bituminous-based torch-on membranes for external tanking, liquid-applied membranes for complex geometries, and sheet membrane systems for large retaining wall applications. The specific system is selected based on the project requirements, soil conditions and hydrostatic pressure levels.
Yes. The New Zealand Building Code Clause E2 (External Moisture) requires that all building elements in contact with the ground must be protected from moisture penetration. For habitable basements and below-ground spaces, a properly designed and installed tanking membrane system is essential for compliance. As a Licensed Building Practitioner, we ensure every tanking installation meets code requirements.
Yes, we regularly remediate leaking basements in Auckland. Depending on the access available and the cause of the water ingress, we can apply internal tanking systems, inject waterproof resins into the concrete, or excavate externally to apply a new tanking membrane. We assess each situation individually and recommend the most effective and cost-efficient solution.
Tanking membrane costs in Auckland typically range from $80–$150 per square metre depending on the system used, access difficulty, ground conditions and the complexity of detailing. Retaining wall tanking is generally at the lower end, while full basement tanking with drainage and protection boards is at the higher end. We provide detailed, itemised quotes after an on-site assessment.
A professionally installed tanking membrane system is designed to last the lifetime of the building — typically 50+ years. The membrane is protected from UV exposure and mechanical damage by the surrounding soil and concrete, which means degradation is minimal. We use only BRANZ-appraised systems that meet the NZ Building Code's minimum 50-year durability requirement for primary building elements.
Contact Matt for a free tanking assessment. We serve all of Auckland.