Client: Residential, private
Our client, a private landlord in Richmond, London, hired Timberwise to survey their property to provide a design for a basement waterproofing system while the property was being converted and remodelled to accommodate future tenants. This property was a house of solid brick construction, and was both unoccupied and unfurnished at the time of inspection or installation of the waterproofing system. Weather conditions at the time of our survey and subsequent works and remediation were sunny and dry over the days we were there.
Challenges
The property was unfurnished and unoccupied throughout the process, owing to it being a property renovation and conversion, so there were no challenges when it came to having to be mindful of residents, personal belongings, or fittings. However, there were some considerations due to the property being an active building site at the time. Whilst we had to be mindful of other work that was taking place in the property, the building was also undergoing significant structural renovation including excavation to bare earth which could have posed safety risks.
Due to the age and construction of the property, our surveyors had to consider the potential presence of asbestos-containing material in the bitumen paint on the basement walls. The client was advised to have it tested by a licensed asbestos removal contractor prior to the installation. Ultimately, no asbestos was found and the project was able to continue unhindered.
One of the biggest considerations was our requirement to meet the stringent BS 8102:2022 guidelines in order to successfully achieve a Grade 3 waterproofing performance level for habitable basement. We also had to manage potential hydrostatic pressure from changing water tables or localised flooding when drafting designs.
Observations
The basement required a full waterproofing design to protect it against future water ingress and to make it a dry, hospitable place for tenants to be able to live in. Our surveyors noted that the internal walls of the property showed signs of a previous treatment, which turned out to be bitumen paint. We flagged the paint with the client for potential presence of asbestos, but this turned out to be fine upon further inspection.
Site photos attached show that the floor slab had been removed and the area was prepared for a new drainage installation. Conditions of the property meant that it required a system that could handle water pressure equalisation rather than just prevention. This was to ensure it remained compliant with BS 8102:2022 standards, to prevent structural load, and offer flexibility and movement. At Timberwise, we maintain that the best way to manage potential water ingress is to manage it rather than outright prevention, through the use of a cavity membrane system and sump and pump station.
Solutions
There were a significant number of preparatory works that had to be carried out before anything could be physically done to the property. As mentioned earlier, we had found the potential presence of asbestos bitumen paint that had to be tested and removed by a licensed specialist. In this case, the bitumen paint was revealed not to contain asbestos.
All redundant pipework in the area had to be removed from the walls and floors in order for Timberwise to fit the membrane system effectively. Anti-lime coating also had to be applied to all concrete wall and floor surfaces to prevent free lime from blocking the drainage channels.
The biggest task was designing and installing an effective Type C basement waterproofing solution. We opted for a cavity wall membrane system that would “catch” moisture and trap it, leading it to a drainage system to be taken away from the property. With this in mind, we installed an 8mm high-density extruded wall membrane that was fixed in place with dual-purpose plugs. For the floor, we installed a 20mm high-density extruded floor membrane which was then further sealed at the joints and perimeters of the basement. We used special patented fixings with gasket seals to maintain the integrity of the barrier.
Alongside the wall membrane, we also needed to design and implement an effective drainage system to channel this collected water from the membrane and have it diverted safely away from the property. We installed sub-terrain drainage pipes into the ground prior to the laying of the property’s new floor slab. We connected this drainage system to an interceptor chamber. We then installed a one-way valve before connecting it to the main drainage system. A sump and pump system was then added to collect and pump this water to an external drainage source in instances where the gravity feed was not viable.
Remaining works included a flood test to confirm that the water flowed into the correct channels with ponding and were effectively removed by the sump and pump system we installed. We also cleaned the system upon completion of the installation. We then provided the client with a Radon test kit to ensure the basement remained at a safe environmental level following further works to the basement.
Results
Timberwise successfully identified defects within the structure and were able to provide the client with a specialist basement waterproofing design for their basement, making it habitable for tenants. The system we installed was fully compliant with BS 8102:2022. We successfully delivered a Grade 3 waterproofing system that would make the area dry, ready for internal wall and floor finishes. Our solution offered the client with a 10-year guarantee for the cavity drain membrane, ensuring long term peace of mind.
Do You Want Help with a Waterproofing Solution?
Our dedicated and experienced team in South London are ready to talk to you about your options for property preservation. Don’t hesitate to call us on 0800 288 8660, or you can request a survey online.
