ew buildings garner such publicity and admiration as the recently completed US Embassy, constructed at an estimated cost of $1bn in the London Borough of Wandsworth.
Described as a crystalline “sugar cube” and a “Modernist museum”, the New London Embassy (NLE) has the accolade of being the most expensive embassy building ever built.
Alongside its stunning architecture and environmentally-responsible building services installation, the NLE also boasts an impressive security specification. The extensive pond adjacent to the building both enhances the public realm around the embassy and provides a defensive border in the form of a moat.
The pond was designed by the project’s American Architect, Kieran Timberlake, and the practice also specified the use of Firestone’s GeoGard 1.5mm EPDM lining membrane, which was installed on site by the construction and civil engineering contractor responsible for the pond, PJ Carey.
Style and shape
Located to the south side of the NLE building, the 6000m² pond is largely semicircular in shape, abutting the embassy along its straight edge, with a dog’s leg bend at 90˚ creating a waterfall at a right angle to the main wall, followed by a further 90˚ bend before it continues along a parallel route. In these areas, the retaining wall is 5m high and borders a walkway around the building perimeter, creating an impactful 5m drop for the waterfall, which is fed by pipework that takes water from the curved wall to the rear of the building.
From each end of the straight 5m walls, the pond curves out into the landscaped gardens. It has been constructed with three terraced dwarf walls along the curved edge, creating a stepped area for planting below the waterline and enabling pedestrians to walk around the pond edge at ground level.
Thanks to the rainwater harvesting infrastructure built into the building, much of the water used to fill the pond will be recycled rainwater, adding to the sustainability of the project. The landscaping around the pond has also been designed to enable water to drain through permeable paths into pipework that leads into the pond. A series of 44 ornamental scuppers act as an overflow to manage the water level in the pond, and any excess water will simply drain into the sewer system.
Lining selection and training
The Firestone GeoGard EPDM membrane was selected for its durability, long service life and flexibility. While the membrane is just 1.5mm thick, its chemical resistance and permanently elastic synthetic rubber structure provide excellent resistance to UV, heat, ozone, microorganisms and extreme weather conditions. With formidable puncture resistance and elongation of up to 300%, the membrane is at low risk of tearing or puncturing, either during installation or due to heave post-completion.
The level of complexity required for the NLE pond lining required an expert approach. Consequently, every member of the PJ Carey installation team was trained by Firestone’s technical team and technical representatives visited the site several times during the course of the project to troubleshoot specific detailing challenges. The Firestone technical team also aided optimisation of the GeoGard EPDM material, calculating the most efficient layout for the project.
For all the vertical substrates, Firestone Bonding Adhesive was roller-applied to the prepared concrete surfaces, and the GeoGard EPDM membrane was applied directly onto the substrate. At the top of each vertical section, the GeoGard EPDM was terminated using a stainless steel termination bar. The GeoGard EPDM was then folded back down over the termination bar, and Firestone’s Lap Sealant was applied onto the exposed edge.
For the terraced walls on the curved edge of the ponds, the installation used 3m sections of GeoGard EPDM to lap the membrane up and over the dwarf walls.
The base of the pond was levelled out by the contractor, and a 50mm layer of bedding sand was installed onto the level surface, followed by a geotextile layer and finally the GeoGard EPDM membrane. Concrete coving was installed around the perimeter of the pond basin and the PJ Carey team lapped the GeoGard EPDM membrane over the coving, bringing it down from the vertical surface and adhering it to the coving. The GeoGard EPDM was also lapped up the coving and a third layer of GeoGard EPDM was applied over the 500mm lap to create a very robust seal.
The east and west sides of the pond each contain two outlets where the water is supplied into the pond from the building’s mains and rainwater harvesting systems. To form these penetrations, the PJ Carey team used Firestone’s QuickSeam FormFlash, an uncured EPDM membrane factory-laminated to QuickSeam tape designed specifically for challenging details. The team also used QuickSeam FormFlash to create 15 drainage outlets of various sizes around the pond’s internal perimeter, to seal the apertures for the scuppers and form all the complex corner and step details.
In addition to these details, the pond installation team also had to prepare 6000 penetrations for the cladding system used to conceal the concrete substrate and connect the pond aesthetically to the building. The PJ Carey team worked closely with the cladding specialist, and the penetration locations were marked out on a grid, prior to installation of the first fix. With the first fix bracket in place, the PJ Carey team sealed each penetration using QuickSeam FormFlash and the penetrations were checked by Firestone’s technical team, using compressed air to verify the seal. The second element of the bracket could then be installed in preparation for installation of the cladding panels.
Attention to detail
Due to the size and complexity of the pond, the project took more than 18 months to complete, and additional planting was still ongoing when PJ Carey handed over the site. As images of the official opening were broadcast around the world, the effort and attention to detail involved were clear to see.