We were asked to investigate a suspected failure of the waterproofing of a newly built basement apartment in Lincoln.
The owner thought something was amiss because the carpet was often wet. When Les Sellers, our senior surveyor, visited the apartment there was around 100mm of water on the floor and the outside light well was flooded. It was hardly surprising that the carpet was wet from time to time. The water had caused considerable damage to the internal decoration, floor coverings, fixtures, and furnishings within the apartment. And all of these items had to be stripped out.
Upon further investigation, Britannia Preservation found the water table to be nearly 800mm above basement floor level. A lack of adequate waterproofing protection was allowing this ground water to flood the light well and seep into the apartment.
The remedial work was complicated because the apartment floor had been constructed as a reinforced concrete raft. This meant that drainage channels that are used to remove incoming water could not be inserted in the floor. Instead, we used an ingenious design and raise the central part of the floor by overlaying it with a cement screed creating a trough at the perimeter into which the drainage channels could be placed.
Water collected by the drainage channels needed to be removed, and this was achieved by installing two sump basins. Because this part of the work involved cutting through the concrete raft, the design was assisted by a structural engineer who detailed the reinforcement to ensure that the concrete raft was not adversely affected. The perimeter drainage channels were connected to the two sump basins using a network of pipes set into the screed. We installed two submersible pumps into each of the sump basins–four pumps in total–and this ensured rapid water removal and protection in the event of a single pump failure.
The floor and walls area were overlaid with cavity drainage membrane. We used a 20mm deep studded membrane on the floors and a standard 5mm deep studded membrane on the wall. The internal linings, fixtures, and fittings were reinstated on top of these membranes. Even though this apartment is permanently below the water table, the cavity drainage system installed has successfully prevented further flooding.
The staining on the walls in the lightwell clearly illustrates the height of the water table. |
The concrete floor slab at the left-hand rear of the apartment permanently covered with water until the drainage system was installed. |
The design of the two concrete sump basins was assisted by a structural engineer. The raft was cut out and new reinforced concrete installed to create two chambers to the sump basins. |
The surface of the cement screed corresponds with the top of the sump basins. At the perimeter of the floor the screed creates a trough into which the Aquachannels have already been placed. |
The floor in the left-hand rear of the apartment after the membrane work is completed, ready to receive the internal linings and finishes. |
Tape is placed over the edge of the membrane where it meets the sump basins to ensure a watertight seal. The white pipe protruding from the floor is for the electric supply cables for the pumps. |
A removal panel is formed in the floor decking to allow easy access to the sump basin and pumps for servicing. |
With the floors overlaid with decking and walls plasterboard dry lined, the apartment can be decorated. |
Finally, the internal fixtures and fittings are reinstated to complete the apartment. The homeowners are assured that they are protected from future flooding. |
The conditions at this property were challenging, with a solution that required careful design and implementation, but the owner now has a comfortable and damp free apartment. Britannia Preservation completed this project in 2010, and despite wetter weather in recent years the apartment has remained perfectly dry. If you have a flooding problem or a basement or cellar that you wish to transform into dry, usable living accommodation, contact us today to find out more about our services.
© Britannia Preservation 2011