Auckland Subsoil Drainage

Subsoil problems are easy to misdiagnose. A lawn that stays wet can be a surface water issue, a groundwater issue, or both, and the fixes are completely different. We work out which one you've got before quoting a solution.

Depth is the thing most people get wrong. A subsoil line has to sit below the level where the water is causing trouble, and a shallow trench through clay does almost nothing except waste a weekend.

We install these lines around retaining walls, under lawns, along boundaries and beside foundations, so we've seen how they behave across most of the situations Auckland properties throw up.

Filter fabric is non-negotiable on our jobs. In clay soils, an unwrapped subsoil line silts up faster than anywhere else, and once the aggregate is full of fines the system is finished. Wrapping it costs very little compared to digging it up again.

We use clean, properly graded drainage metal rather than site fill. The whole system depends on the void space in that aggregate, so filling the trench with anything that has fines in it defeats the purpose before you've backfilled.

And we plan the outfall first. Groundwater has to discharge somewhere it can keep moving, and a subsoil line that ends in a soakage pit already sitting in a wet clay pocket just moves the water two metres and stops.