Case Study / Waterproofing

Listed house, Hampstead Heath

Delivering a bespoke design to a prestigious residence in London

MacLennan have recently finished work at a phenomenal house in Hampstead Heath, built originally nearly 150 years ago. This grand Victorian property sits in an elevated position surrounded by seven acres of landscaped grounds with impressive views across London.

Requisitioned by the government during World War II it served as an RAF training school, later being converted into a geriatric hospital. It remained as an NHS hospital right up until 2003, when it was sold to a firm of investors for redevelopment. For the past 16 years the property sat empty, gradually falling into disrepair. But about three years ago it changed hands once more, bought by a private client who has resolved to restore and improve the property and return it once again to residential use making it into a
family home.

After undergoing an extensive two-year restoration programme, in keeping with the original architectural style, the property boasts spectacular exterior features including Dutch gables, castellations on the tower and Victorian chimney stacks. It was designed by SHH Architecture and Interior Design and is now a modern six-bedroom house along with several outbuildings including a new pavilion, entertaining space, a gatehouse and cottage providing additional guest accommodation. Contractor Knight Harwood invited MacLennan to come up with waterproofing design, supply and installation.

Method

MacLennan designed, supplied, and installed a fully compliant bespoke waterproofing system across the existing basement, the new basement plant room and the pavilion as well as lightwells, lift pits, tree pits and planters. Each area had to have a bespoke design to fit the needs of the area as well as accommodate the differing construction types. All areas were waterproofed to grade 3 needing a combination of type A, B and C waterproofing. MacLennan carried out our crystal coat waterproofing of the new concrete areas which provides a mixture of type A and Type B waterproofing before applying a type C cavity membrane system.

In the existing areas a cementitious tanking system was installed to existing prepared brickwork to give two forms of
waterproofing before applying the Type C cavity membrane system. An external system would have been too
destructive to conservation of the grounds.

The system is fully serviceable and maintainable with a total of 5 state of the art pumping stations to deal with any potential water ingress.

The MacLennan Polyprufe system was installed to the deck areas and the green roof of the pavilion making them fully watertight.
We needed to stem an active water ingress to the existing basement before we could carry out our works. This was carried out by our resin injection team.

There were some very specific details required for the
job. We waterproofed the movement joint linking the existing basement and the new basement. This included a bespoke design using a robust flexible combi flex detail to a projector cut out which protruded from one basement to the other (used as a cinema room).

Result

The work was carried out to BS8102/2022 waterproofing standard, within the budget and in the agreed time frames and is guaranteed for a period of 10 years.

No Split Liability.