London, United Kingdom
HAL Architects created this one-of-a-kind “Sky Pool,” a cast and bonded acrylic swimming pool slung 10 storeys up between two towers in Embassy Gardens, a residential development by EcoWorld Ballymore opposite the new US Embassy in Nine Elms, London.
The Sky Pool has recently been awarded a 2022 International Architecture Award by The Chicago Athenaeum: Museum of Architecture and Design and The European Centre for Architecture Art Design and Urban Studies.
Since opening this summer, the pool has become the unintended focus for wider discussions on social equality; but there is no taking anything from the fact that the pool itself, 10 storeys above ground, is an engineering feat, a close collaboration between architect, engineer and fabricator to meet the client’s desire for a radical statement at its riverside development.
Sky Pool had been four years in the making.
Initially conceived as a swimmable aqueduct, the design process evolved to make the most of unparalleled views across London.
The requirement to fit a 25m pool at 10-storey height, and conflicting rooftop plant demands, spawned the idea of using the pool as a viaduct between the two buildings; it was also directly accessible from both towers.
Made of crystal-clear acrylic, it spans 15 metres, ten storeys up, between two apartment buildings. There is nothing else like it.
Engineering concerns included the weight and hydrostatic pressure of 150t of water on the pool floor and walls, horizontal wind loading and differential vertical settlement of the two concrete towers, as well as the pool’s skewed relationship to them.
Add to this the intrinsic thermal expansion of the acrylic itself, and differential stresses between outside and pool surfaces and the engineer had plenty to consider.
Its response was a cast and bonded acrylic ‘U’ form made of six 356mm thick floor pieces and four 3m high 178mm thick wall sections, the latter acting as two enormous beams.
This monolithic acrylic element is sandwiched bet¬ween two 5m long steel ‘tubs’ sat on the two towers, containing steps, lighting and filtration equipment.
Holding the three pieces together are two pre-tensioned steel tendons running between the steel tubs.
These connect to a spring stack either side which accommodates thermal expansion and contraction of the acrylic of up to 80mm while holding the structure in constant tension to avoid leaking.
The whole structure sits on 10 bridge bearings on the concrete towers, which allows them and the pool structure to move relative to each other.
It was one of the most challenging designs the firm had worked on.
Project: The Sky Pool
Architects: HAL Architects
Structural Engineers: Eckersley O’Callaghan Engineers
Fabricators: Reynolds Polymers
Client: EcoWorld Ballymore
Photographers: Simon Kennedy
