Case Study / Waterproofing

Luxury Home, Beaconsfield

Comprehensive Basement Waterproofing

MacLennan were approached by Belvedere Contractors to provide specialist waterproofing expertise for a high-end residential project in the prestigious area of Beaconsfield.

The project involved the construction of a new basement and an extension to an existing family home, designed to enhance both the functionality and luxury of the property.

The basement was designed to include a wine cellar, gym, and sauna—spaces that require a dry, controlled environment. Half of the basement extends beneath the driveway, while the other half supports a garage and office space above. Given the complexity and high value of the build, the client opted for MacLennan’s full-service package, which includes design, supply, and installation of the waterproofing system.

During the consultation phase, MacLennan recommended a superior alternative to the originally proposed concrete additives, ensuring a more robust and maintainable waterproofing solution.

Method

Waterproofing Strategy

In accordance with BS8102:2022, which mandates considering two forms of waterproofing if the consequence of a leak is unacceptable, for habitable Grade 3 environments, MacLennan designed a dual-system approach to eliminate the risk of water ingress.

Primary Protection – CrystalCoat System: The first line of defence involved the application of MacLennan’s Crystal coat system to all retaining and ground-bearing elements of the basement. This crystalline coating penetrates the concrete to react in the concrete with free lime to form a permanent barrier against moisture ingress.

Secondary Protection – Type C Cavity Drain System: The second and most critical layer of protection was a Type C Cavity drain membrane System. This maintainable system is designed to manage any water that penetrates the structure, channelling it safely to a sump and pump system. Its maintainability makes it the most reliable and guaranteeable component of the waterproofing design. It is the only form of waterproofing which can be tested and accessed for repair as required by the British Standards.

Technical Detailing

Basement floor waterproofing: MacLennan installed 50mm of insulation directly onto the concrete slab, followed by an 8mm cavity drain waterproofing membrane. This method was selected for its efficiency and practicality, as it eliminated the need for a perimeter rebate, simplifying the construction process while maintaining full compliance with BS8102:2022 standards.

This approach provided a robust and maintainable waterproofing layer, ensuring long-term protection and performance for the habitable basement environment.

Head of Wall Detailing: Special attention was given to the detailing at the top of the retaining walls—a commonly overlooked area that can lead to significant warranty claims. MacLennan ensured this critical junction was properly sealed and protected.

Deck and Terrace Waterproofing: The ground floor terrace areas were waterproofed using MacLennan’s PolyM system, a high-performance liquid-applied membrane ideal for exposed deck areas.

Results

MacLennan successfully delivered a fully compliant, dual-layer waterproofing system tailored to the unique requirements of this luxury basement development. The installation was completed on schedule and within budget.

All works were backed by MacLennan’s robust guarantees and covered under our £10 million Professional Indemnity insurance, providing complete peace of mind to the client and project stakeholders.