Shellharbour French Drain Case Study: Stopping Neighbour Runoff & Subsurface Water

The Damp Problem

A Shellharbour homeowner was dealing with a serious and worsening water ingress issue. Water from two neighbouring properties — both sitting higher than the client’s block — was flowing into the yard and tracking under the slab. The result: damaged new flooring, rising damp, and mould taking hold inside the home. Recent renovations were at risk.

The Diagnosis

The source was both surface runoff and subsurface water migrating downhill from the rear and side neighbours yards. With no adequate drainage intercepting it, the water had nowhere to go but under the house.

The Solution

CS Plumbing designed and installed a gravity-fed French drain system to intercept and redirect the water before it could reach the slab.

The scope of work included:

• A French drain system to capture surface and subsurface water from the neighbouring boundaries, diverting it via gravity to a concrete pit
• 100mm PVC pipe running from the pit to the kerb, with neat holes drilled into the kerb for discharge
• Three new, larger-diameter Colorbond metal downpipes replacing the two smaller originals, connected into new 100mm PVC pipework running to the kerb
• A retaining wall system along the boundary using concrete sleepers and galvanised steel posts, with auger holes drilled using an excavator — an engineered solution to physically hold back the neighbouring yard
• Soil removal on-site using a dumper

The Outcome

Surface and subsurface water is now intercepted at the boundary and diverted away from the property entirely. The client has a permanent, low-maintenance solution that protects their slab, their floors, and their investment in the renovation.