With some exquisite finishes, the frame of Lifschutz Davidson Sandilands’ JW3 is elegant as well as tough, writes Felix Mara. Photography by Hufton + Crow
JW3, a secular Jewish cultural and community centre designed by Lifschutz Davidson Sandilands (LDS) and opened with a fanfare of high-profile events last September, seems more focused on its future than its historic context. Bus drivers used to call the section of Finchley Road on which it sits ‘Finchley Strasse’ after it was flooded with Austrian refugees at the time of the Anschluss. Over 70 years later, the demography of the NW3 postcode the centre takes its name from has shifted, and memories of ‘the old country’ have faded. This is a community centre in the broadest sense of the word, open to anyone interested in Jewish culture whatever their faith or ethnicity, reaching out to the Home Counties and beyond. The opportunity to design a new building where there was once a car showroom and a block of flats enabled LDS to start from first principles, especially in JW3’s bones: its structural frame.
The two essential principles were that JW3 should be loose fit and permeable, so it could adapt to changing needs and attract visitors. Comprising a four-storey pavilion with a mezzanine-level bridge across a piazza leading to the centre’s main entrance, and an adjacent tower with replacement flats, the development’s logic is crystal clear. Accommodation in the pavilion becomes increasingly private as the Shabbos-compliant lift, which can function without being manually operated by the orthodox, rises up the building. At ground level there is a multi-purpose hall, restaurant, café, bar and screening room; on the top floor a nursery.
But the configuration of these spaces and those on the intermediate floors is adaptable.
If you cut a cross-section through the pavilion, you can see an ancillary zone including service spaces and risers on its west side, where windows would overlook neighbouring residences, whereas the main activity areas are in wider spaces on the glassy east elevation. Below second-floor level, a corridor separates these zones. By providing a glass barrier, a ground floor which is below street level, insulating units and acoustic baffles, LDS has blocked the traffic thunder of Finchley Road, and was even able to naturally ventilate nearly all the spaces using the stack effect to exhaust air through rooftop cowls.
Although the options of steel and timber were floated, LDS expressed a preference for a concrete frame with a high-quality visual finish and, together with structural engineer AKT II (which contributed to the AJ article on visual concrete in AJ 02.09.10), looked at various strategies including waffle and void slabs. They settled on a ribbed slab configuration which facilitates services routing through floor zones, and also allows for adaptability. These ribs, which are 350mm deep and 175mm wide, run east to west on a 1.2m module, spanning 10m between two runs of primary beams at 7.2m centres and supporting a 125mm topping slab. The run of beams between the corridors and the ancillary zone is below the ribs and can be hidden in walls. This configuration enables service connections in the floor which pass between ancillary and open activity zones to be routed over these beams. LDS wanted the ribs at mezzanine level to march on into the multi-purpose hall but here, because the space is larger, they hang from an upstand beam to avoid increasing the depth of the floor zone. This upstand is in turn suspended from a roof-level transfer beam.
‘LDS wanted to use concrete as a defining element of the architecture and push the boundaries,’ says AKT II director Gerry O’Brien. ‘From the point they decided exposed concrete was the correct solution, we worked very closely with them to develop a specification to control the frame procurement.’ The concrete details were crucial, and LDS eschewed the usual language of chamfered corners. Rather than evaluating the alternatives of 25 x 25mm or 20 x 20mm corners and getting involved in three-way chamfers, which can look like a microcosm of hipped roof geometry, LDS opted for sharp arrises that demanded a suitable concrete mix at the face and shutters, and could be tightened up in these locations. As a further refinement, LDS also wanted to plug visible shutter bolt holes with small concrete cylinders.
‘It was all about the quality of the workmanship,’ says O’Brien. ‘The ribs, which had a 20mm precamber, were formed in situ, which meant all falsework and formwork had to be precisely manufactured on site to ensure uniform joints, and exceptionally tight mitres and corners between the timber shuttering.’ In-situ concrete subcontractor Getjar had a highly equipped woodworking shop on site where industrial table saws were used to create perfectly matched and mitred joints.
‘A blended cement was used which had 30 per cent pulverised fuel ash (PFA), resulting in a dark concrete,’ says O’Brien. ‘The mix design selected was self-compacting concrete, and 10mm limestone aggregate was specified along with a low water-to-cement ratio of 0.32, with film-faced plywood for the form face.’ If the ordinary Portland cement substitute, introduced to minimise CO2 emissions, had been ground granulated blast furnace slag (GGBS) rather than PFA, the concrete would have had a much lighter colour.
The client team visited reference buildings to establish what could be achieved when concrete is well designed, specified and constructed. LDS selected buildings named as benchmarks in the specification. ‘This set stringent requirements for workmanship and accuracy, requiring detailed method statements to be agreed early in the process and rigidly applied throughout the works: every pour, every element from beginning to end,’ says O’Brien. The specification also required sample panels, enabling various mix designs to be evaluated and allowing the contractor to assess buildability. The design team’s rigorous documentation and procurement strategy was underpinned by the commitment and aptitude of the main contractor and Getjar.
A full-size mock up incorporated critical details, including a column and stairwell section as well as primary beams and the ribbed slab. This allowed the architect and contractor to assess what could be achieved, and make tweaks to improve constructability and the outcome. The mock up confirmed that LDS’s requirements, including precise, square corners on columns, walls and beams without fillets and rebates for stair stringers, could be achieved using well-compacted concrete. It was also an opportunity to review formwork setting out and articulation, lifting eye details and cover plugs.
In contrast, all external concrete uses Portland cement to achieve a white finish and was precast, with vertical flutes cast into the tower cladding panels which were rotated for a random effect. It’s a credit to the quality of the design, specification and workmanship that the internal in-situ concrete rivals the quality of the external precast, and JW3’s frame is a happy marriage of intelligence and good looks.