Residential Service
Residential
Below-Ground Waterproofing (Exterior)
Overview of the service
Below-ground waterproofing protects foundations, retaining walls, and subfloor areas from water ingress and moisture damage. It is suitable for brick, block, breeze block, and concrete walls below ground level.
BlastOff Solutions installs external moisture barriers using a 4mm SBS torch-on membrane, protection board, drainage scoria, and a Novacoil subsoil drainage system connected to stormwater or a sump and pump, followed by scoria backfill.
The system is installed to meet NZBC Clause B2 (Durability) and Clause E2 (External Moisture), preventing leaks, dampness, and long-term structural damage.
How we waterproof
below-ground walls
Our process targets the source of the moisture – outside the wall – with a code-compliant tanking system designed for the life of the building.
Each home is assessed on site before quoting so you know exactly what the work involves and what it will cost.
01
Excavate along the wall to footing level
02
Prepare and prime the wall surface
03
4mm SBS torch-on membrane applied
04
Protection board, drainage scoria, Novacoil drain
05
Scoria backfill and surface reinstatement
Where this
service is used
Below-ground waterproofing is commonly required for:
01
Older homes with concrete block, brick, or breeze block
02
Pre-2000s homes with flint coat or no waterproofing
03
Basements and lower levels with damp or mould
04
Retaining walls and subfloor moisture issues
05
Foundations needing protective upgrades
Frequently asked questions
How do I know if I need below-ground waterproofing?
Damp smells, water staining, mould, bubbling paint, peeling skirting, or visible moisture on lower walls. If your home was built before the early 2000s with concrete block walls, it most likely had only a flint coat — a basic spray with no drainage — which fails over time and needs upgrading to proper tanking.
Why won't sealing the inside walls fix the problem?
Water comes from outside, so the fix has to be done from the outside. Sealing the inside just traps moisture and the wall keeps deteriorating. Internal sealing has no drainage and no protection layer, so it can’t relieve the water pressure pressing against the wall. Over time, trapped moisture breaks down the block, corrodes the reinforcing steel inside, and the wall eventually fails. Anything less than external tanking with subsoil drainage is a band-aid.
What does the work actually involve?
Five stages: excavate along the wall to footing level, prepare the surface, apply 4mm SBS torch-on membrane, install protection board with drainage scoria and a Novacoil subsoil drain to stormwater or a sump pump, then scoria backfill and reinstate above.
How is the excavation done, and what if access is tight?
We hand-dig every job. There are plumbing pipes and services around the outside of a house that a digger can damage, so hand-digging gives us full control and lets us work where machines can’t go — tight side passages, under houses, behind walls, and sometimes from inside the house when outside access isn’t possible. Every site is assessed before quoting so you know exactly what’s involved.
Will my garden, driveway or landscaping be damaged?
Excavation is disruptive — there’s no way around that. We dig a neat trench about 600mm wide by the depth needed to reach the footing. We protect what we can, lift pavers carefully for relaying, and reinstate soil and surfaces above the work zone. We do our best to put everything back the way we found it, but some plants and grass in the dig zone won’t survive.
How long does the job take, and do I need to move out?
Most jobs take 1 to 3 weeks depending on wall length, depth, and access. You don’t need to move out — the work is external and the house stays liveable throughout.
What does it typically cost, and what affects the price?
Most residential jobs sit between $10,000 and $50,000. A single wall at average depth is around $10,000; multiple walls or deeper digs push toward the upper end. Price depends on wall length and depth, site access, what needs lifting and reinstating above, and drainage connections. Every job gets a free site visit and written quote.
What's the warranty, and what happens if it leaks again?
The system is installed to meet NZBC Clause B2 (Durability), which requires 50 years’ minimum durability for below-ground waterproofing, and Clause E2 (External Moisture) for keeping water out. The 4mm SBS torch-on membrane is BRANZ-appraised for 50+ years. On top of that, we provide a 10-year workmanship warranty — if the system fails due to our installation, we come back and fix it.
Ready to protect
your home?
If you’re dealing with moisture or water ingress, get in touch with BlastOff Solutions. We can assess your home and recommend the right waterproofing solution.