Oak Tree House


The Problem

Oak Tree House is a newly built detached property with a large basement designed to house a cinema room, bar, gymnasium and wine cellar and which also houses the plant room for this substantial home. Although the basement was originally waterproofed, complete with a drainage system around the external perimeter, water ingress was flooding the basement regularly after heavy and prolonged periods of rainfall. Two sump pumps, which had been retro-fitted into the floor of the basement, were in daily use and the client was considering adding another six sump pumps as a solution to this chronic groundwater/flooding problem.

On securing this installation, GWD advised the client to cancel the order for extra sump pumps and also to prepare to remove the two existing sump pumps within weeks of the installation being complete. It took just two weeks from the beginning of the installation for the existing sump pumps to dry out and be removed. Our EGRP system effectively cancelled out the hydrostatic pressure around the basement walls and floor, and there was a subsequent 1500mm drop in the level of ground water leading to a completely dried out basement within three months of our installation.

Why use the EGRP the solution?

With minimal disruption whilst the install was taking place, and without the need to dig drainage trenches, other building works at the premises were able to continue as normal during our installation. The EGRP system, which in this instance sits 600mm below ground level, does not require any ongoing maintenance or external energy source and once installed enables the homeowner to finish off whatever landscaping/finishing is required at ground level.

System Design

Following a thorough site investigation and examination of localised borehole records a detailed design was produced which involved drilling some 134 bore holes to depths of up to 12 metres around the perimeter of the property. This vertical drainage system intercepts groundwater as it moves from an area of higher ground towards the property, dropping the level of groundwater as it meets a wall of vertical drainage devices, subsequently lowering the level of groundwater underneath the building.


A 3.0 tonne Comacchio specialist drill-rig, mounted on track mats, was used to drill holes at varying depths from 1.5m to 12m deep. EGRP devices were capped and then vertically inserted into the bore holes respectively, penetrating the heavy clay sub-soil before reaching layers of unsaturated ground below. Also, due to there being a large amount of services located around this new build property GWD dug a number of trial inspection pits in order to locate gas/electric/water/telecoms/sewage and drainage pipes before drilling commenced.

Key features

Retro-fit complete drainage system causing no disruption to other construction works

No outflow to land drainage or soakaway required

Deals with rainfall at source – recharging groundwater aquifers

Energy-passive requiring NO external energy source

“The EGRP system has provided an effective solution for a problem which conventional waterproofing solutions failed to deal with. Ten days into the three week installation the main sump pump was only in use for 20 minutes a day instead of all day and now both pumps have been removed. My basement is dry and work can continue.’’ - Homeowner Mr M. Mann