Get the water out of the ground.
Some water problems aren’t on the surface. The lawn stays soft for days after rain, the subfloor smells damp, an internal wall shows rising damp, and the stormwater system is working perfectly — because this water is in the soil, not in your pipes.
Available 24/7 across the North Shore · No callout fee on eligible jobs
Sub-soil drainage intercepts groundwater below the surface and takes it away before it reaches your foundations, subfloor or retaining structures.
The distinguishing feature is that clearing the stormwater doesn’t fix it. If your gutters, pits and lines are all clear and the ground is still wet, the water isn’t coming from your drainage system.
Two local factors:
Add older homes with suspended timber floors and minimal subfloor ventilation, and you get the classic North Shore damp subfloor.
Describe what’s happening and we’ll tell you straight — including when the simple fix is the whole job.
A perforated pipe is laid below ground in a gravel-filled trench, wrapped in geotextile filter fabric to keep silt out. Groundwater moving through the soil enters the pipe and is carried away to a legal discharge point — a stormwater connection, a pit, or a suitable outlet lower on the property.
The details that determine whether it works for a decade or clogs in two years:
Where the issue turns out to be surface water rather than groundwater, you’ll be told that — the fix is a trench drain and it’s usually cheaper.
— perforated pipe below ground, intercepting groundwater across an area. What this page covers
— a gravel-filled trench, with or without pipe, typically used along a specific line such as a retaining wall or the uphill side of a house. Same underlying problem, specific application
— a grated channel at the surface, catching water running across paving or a driveway. Different problem entirely
If your gutters, pits and stormwater lines are clear and the ground is still waterlogged, it’s groundwater. If water is backing up out of a grate or the gutters overflow, it’s stormwater.
It can be either. A leaking pipe under the house produces damp that doesn’t vary with the weather; a groundwater problem gets worse after rain and improves in dry spells. Leak detection rules the first one out.
A legal discharge point — usually a stormwater connection or a suitable outlet lower on the site. This is the part that’s most often done badly, and a system without a proper outlet doesn’t work.
Properly installed with filter fabric and correct fall, many years. Systems fail early when fines get into the aggregate and silt up the line — which is what the fabric is there to prevent.
Often it addresses the cause, by removing the groundwater feeding it. Whether the damp itself needs additional remediation depends on how long it’s been going and what it’s affected.
Sometimes, particularly where the discharge point involves a council connection. Voyager will flag it before quoting.
Free quote, a fixed price agreed before the work starts, and someone on the end of the phone at any hour.
Voyager Plumbing · NSW Contractor Licence 476657C
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Page reviewed and updated 19 August 2026
