Case Study / Waterproofing

New Basement, Exeter

Waterproofing Design and Installation for a Luxury Basement

MacLennan were commissioned by the architectural team to provide expert consultation and installation of a comprehensive waterproofing solution for a high-end residential extension featuring a single-storey basement. The basement was designed to house a luxury wellness suite including a swimming pool, gym, spa, massage room, yoga studio, and shower facilities.

Given the complexity and intended use of the space, the architect required MacLennan’s specialist input to ensure the waterproofing design complied fully with BS8102:2022 – Code of Practice for Protection of Below Ground Structures Against Water Ingress. The scope also included waterproofing design for the external terrace areas situated above the basement structure, which would be subject to landscaping and external finishes.

MacLennan’s involvement was not limited to installation; we were engaged from the early design stages to provide a CSSW-qualified waterproofing strategy that would meet the performance expectations of third-party warranty providers such as NHBC, GPI, Premier Guarantee, and BLP, while ensuring long-term durability and serviceability.

Method

Design Compliance and Strategy
Initial documentation and architectural drawings indicated the requirement for a Grade 3 environment as defined by BS8102:2022. A Grade 3 basement is suitable for habitable use, where no water ingress or dampness is acceptable. This classification necessitates a robust and multi-layered waterproofing approach.

In line with BS8102:2022 recommendations, MacLennan implemented a combined protection strategy, integrating multiple waterproofing systems to mitigate risk and enhance reliability. This approach is particularly critical for structures with high water tables or complex usage profiles, such as wellness facilities.

Buried Roof Waterproofing
As the basement extended beyond the footprint of the main building, the roof structure was to be buried beneath external landscaping. This required a highly durable and seamless waterproofing solution.

MacLennan specified and installed the Polyurea system, a high-performance, liquid-applied membrane designed for exposed decks, podiums, and buried roofs. Key features of the system include:

Fast-curing, elastomeric formulation for seamless application.
Long-term durability under soil and hard landscaping.
Full compliance with BS8102 and third-party warranty requirements.

All detailing around posts, penetrations, and fittings was carried out by MacLennan’s waterproofing specialists to ensure continuity and eliminate potential weak points. This level of detailing is essential to avoid split liability and ensure the integrity of the waterproofing envelope.

Results

MacLennan successfully delivered a fully integrated, dual-layer waterproofing system tailored to the unique requirements of this luxury basement development. The project was completed on time and within budget, with all works carried out in accordance with British Standards and warranty provider specifications.

Key outcomes included:

Zero water ingress, meeting Grade 3 performance criteria
Full compliance with BS8102:2022 and warranty provider standards
Robust guarantees backed by MacLennan’s £10 million Professional Indemnity insurance
Peace of mind for architects, engineers, and clients through expert design, installation, and long-term support