Basement Waterproofing at The Lewis Building, Liverpool

Background to Case Study

Our North West basement waterproofing specialists were called out to the historic Lewis building in Liverpool city centre, to carry out a waterproofing survey and create a robust waterproofing solution to protect the structure from water ingress at ground level and below. The property is a large grade II listed city centre building formerly used for retail and office space however; the property has remained derelict for over 10 years and was in need of restoration. As part of the restoration works the property is undergoing development for habitable use and as such areas below ground are in need of waterproofing as shown below.

Prior to Timberwises involvement

During the surveyors inspection it was evident that the footprint to the ground floor and the lower ground floors were very similar, however, the basement of the property had a reduced footprint which had to be taken into account when designing the waterproofing system.

The property had already undergone part renovation to the internal walls as well as having staircases and lifts, door frames and doors installed – all of which were at varying levels – which implies that the floors are planned to be “built up” – with the exception to this been the basement area where the lift and door levels were at the existing floor level. In parts, render has been applied to the walls to protect it however this had become cracked and delaminated over time as a result there was also mould developing as a result of water ingress shown below.

Within the basement there appears to be a series of below basement drainages and manholes. We recommended installing a land drainage with a one-way valve to prevent issues with backing up.

Graham Malpass, North West Surveyor

There was some standing water within the basement and a leaking pipe was evident in one area, as shown below. Overall, the floors and wall floor junctions were damp and showing evidence of moisture, this would suggest that water was entering the basement during times of heavy rainfall, therefore increasing water levels within the basement.

Additionally, it was also suspected that other sources of moisture ingress such as lateral penetration of capillary held moisture and moisture penetration through the wall/floor joint.

Considerations

Whilst designing a suitable waterproofing system to protect the structure from future water ingress, there were a number of considerations relating to the building that needed to be taken into account. For instance, it’s proposed uses and the likelihood of water ingress or pressure of water building up on the structure during the lifetime of the building. The property is Grade 2 listed and as such this can limit the waterproofing designs away from a more permanent waterproofing protection to a removable one. A waterproof render system was considered to cope with the water pressure from the walls only however, the concern that the likely pressure of water to the walls and floors, particularly to the basement cause issues with the structure in the future. The preparation required to the walls for a render system, particularly where oil and loose wall mortar is present, is likely to hinder a render system. The walls throughout are made of mixed standards and finishes, with many protrusions and preparation of these prior to waterproofing should also be considered.

The River Mersey is within half a mile of the property and whilst somewhat below the levels of the property, we still had to consider this in our design constraints. The property lies to the base of a significant incline from Mount Pleasant and levels of water could be significant, bearing on the property. Overall, the retaining walls of the property and the basement floors were damp and penetration was evident.

Solutions and results

Our Timberwise waterproofing experts designed a system in accordance with the current British Standard – BS8102:2009 “The Code of Practice for Protection of below Ground Structures against Water from the Ground”. Taking into consideration the construction of the property, the usage and the restrictions, our team considered a range of options to meet the requirements for the property. The majority of the areas needed to be waterproofed for habitable use. The basement did have plant rooms and as such a grade 2 environment would be created. With the constraints of the listed building, a system which can be removed will be needed. As the strength of the floor was unknown, our experts proposed the installation of a water management system in the form of a cavity drainage system.

The installation of a cavity drainage system, starting on the walls suffering from ingress to the ground floor, leading through to the lower ground floor and channelling any dampness, water ingress or vapour through the floor to a further system to the basement level. Within the lower ground floor where the floor substrate is presumed to be earth, proposed cavity drainage to the floor. There would also be a soffit detail to collect water from above and to the basement a further soffit detail and cavity drainage membrane to the floor, supported by drainage channels.

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