Basement waterproofing for a three storey detached apartment duplex


20mm floor membrane, 2 x No. 650mm cubed sump chambers


A Victorian spa town nestled within a designated Area of Outstanding Natural Beauty and often affectionately known as “the heart of Yorkshire”, North East Surveyor Martin Wilkinson was called upon to carry out a survey on a three storey detached apartment duplex in one of the most sought-after areas in Harrogate. Martin was instructed to inspect the lower ground floor basement, as the client wanted this to be converted into habitable accommodation as well as an extension, this would include a lounge with adjoining snooker room, a wine cellar, exercise studio, hallway and cloakroom.

The client knew they could trust our Timberwise Basement Waterproofing Contractors to design, install and guarantee a solution that would not only meet all of their specific needs but also met NHBC guidelines, as the new extension that would be built must have two forms of waterproofing in the form on an external barrier and an interior barrier.

The Waterproofing Methodology

Due to the age of the property, and before work could commence, it was necessary to bring to the client’s attention that during the excavation it was quite likely that historical asbestos use may be uncovered, fortunately this was not the case, work could carry on and the site was in line with safe asbestos working regulations. With the new build extension a Type A system, external waterproofing to the outside face of the structure, was the best solution combined with a Type C system was to be applied to the entire internal surface of all of the rooms.

Type C

A Type C system involves the use of cavity drain membranes to walls and floors, also to include for internal drainage channels and pumping stations as a means of exiting water from the basement.

Cavity drain membrane was applied vertically to the walls together with a membrane that was fixed horizontally on the floor alongside a perimeter drainage channel, two separate sump chambers both incorporating two pumps. The pumps were installed with a full battery backup, giving the customer complete peace of the mind that the system will still work in the event of a power failure.

The installation of a new floor slab by the builder it was important that this was treated with a lime pre-treatment to ensure that there were no deposits that would track through and potentially block the free flow of water on the floor between the membrane and the slab prior to it entering the channels/sump chamber. With such a large amount of internal works to be undertaken post completion of the membrane works it was very important that the client understood exactly how the various fixtures and fittings were to be affixed to the wall to ensure they did not puncture the membrane which would then cause the waterproofing system to be redundant.

Such site conditions can be challenging and certainly require a very close liaison and project management working together will the builder to ensure that we were on site exactly when were required but also the builder understood exactly what was required of them to ensure that our works could carry on unimpeded and in line with expectation. Ultimately following completion of the works the entire subfloor section of this building including the new extension was completely dry clean and water free and with the installation of a central spiral staircase made for a real feature within the property.

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