Basement waterproofing as part of a £30 Million commercial redevelopment in Seal

Products Used: cavity drain membrane, sump pump, waterproofing slurry.


Set in acres of Kent countryside and less than 2 miles from Sevenoaks, the estate is made up of 23 one and two-bedroom apartments in the historic main house. Positioned alongside is a charming collection of two-bedroom mews houses that have been built on the site of the old stable block.

The Grade II listed Georgian main house is now beautifully restored to high-end retirement residences. As part of the extensive renovation works, the basement needed to be watertight to create living quarters for the onsite cleaners and a buggy store. The basement walls are made of traditional stone and brick, and the floor is concrete. Although there was evidence of previous attempts of waterproofing, there were other sources of moisture entering the basement.

Timberwise designed the waterproofing system specifying the use of a cavity drain membrane (Type C) system internally. This is designed to achieve a dry habitable living space, defined as a grade 3 environment under BS8102:2009.

Did you know?

Dorton House, formerly known as Wildernesse House, was used as the headquarters for the Royal London Society for the Blind (RLSB) and as housing for the blind and partially sighted children who attended its school until 2013.

BS8102:2009 considers that a Type C drained protection type of waterproofing is the most effective and trouble-free form of waterproofing. The method relies on managing the ingress of water rather than preventing it and means that water pressure is equalised, in that water is allowed to flow freely and is routed to a drainage facility with a sump to be pumped out of the property.


Buggy Store

Within the store, Timberwise Technicians brush hammered the brickwork and made sure to re-point and seal large holes in the brickwork ready for the application of 2 coats of NB1 waterproof slurry.

The brickwork was then treated with Koster Polysil TG 500. An “anti-lime” coating that reduces the amount of free lime leaching into the cavity drainage system as when new concrete forms the structure to walls or particularly floors, there is a risk of excess free lime and mineral salts leaching out during the curing process as this lime build-up can lead to blockage of the drainage cavity and perimeter channel. 8mm membrane was then applied to the walls and vaulted ceiling and fixed using waterproofing batons.

The perimeter drainage channel was then laid down and a liquid waterproof resin to the floor to seal the concrete. The perimeter channel is engineered to collect water at the bottom of cavity drainage membrane and to intercept water coming in under pressure at the wall-floor junction. Ultimately water is then drained or pumped to a drainage point. Ply boards were applied to the roof following the contours of the vault and the vertical walls.

Cleaners Quarters

Timberwise technicians removed the existing plasterboard and waterproofing membrane and brushed hammered the soil retaining walls ready for two coats of NB1 waterproof slurry.

The wall and floor system has been specifically designed for below ground installation and is a high density extruded membrane moulded in a stud formation. The studs serve to hold the membrane away from the wall, allowing water to move freely behind the system and to drain away. In this way, water pressure does not build up behind the substrate or the membrane. The membrane also acts as a water vapour barrier.

Timberwise Technicians then excavated the new sump chamber and installed a double sump and pump. The pump itself comes with a high-level alarm, and a battery backup should the power fail. It was essential to preserve the building’s aesthetic and as the acid in bird faeces could have potentially damaged the buildings stone façades, Timberwise installed a sympathetic and humane bird proofing solution to the porticos of the main house.

Timberwise embraced the challenge to shape the development further and provide Wildernesse House with further facilities creating a modern home while keeping the features of a historic country estate – Timberwise South East 

Waterproofing Design Specialist


The overall end project reveals light and spacious open-plan living areas all while preserving the rich heritage and original features to restore the house, and its grounds, to their former glory.

Speak to a Waterproofing Design Specialist in Seal

All our basement solutions also benefit from our design and installation services along with our long-term insurance backed guarantees ensuring you have complete peace of mind that your basement will remain dry for the year to come.

You can trust Timberwise to provide you with the right basement waterproofing systems to suit your project. Don’t hesitate to contact Timberwise via our form above, by calling on 0800 288 8660 or you can request a survey online.