Sixties superstar enjoys career revival as Costco

I’m visiting Stevenage on one of the hottest days of the year, making my way on foot from the train station. The sunlight is blinding, reflecting off every 1960s concrete surface around. The new town’s famous road network is melting. Its pedestrian and cycle system is fully exposed to the sun; I have to pause in the foot tunnels for respite. I’m weaving up and down in channels between and beneath a grid of dual carriageways, unsure where to turn or whether I will be able to follow my Google Maps route without having to run across a motorway.

At my destination, a blanket of unnatural looking, pristine newly laid turf is being watered round the clock. I’ve emerged on the edge of Gunnels Wood Road into a zone of fast-moving cars and single-occupier office buildings surrounded by parking lots. Fujitsu’s £60m campus is just behind me. In the hottest week of the year I’m here to see one of my most hotly anticipated buildings of 2019. A frenzy of activity heralds this evening’s opening. Caterers are fluttering between marquees, architects have descended to coordinate finishing touches, tradesmen are making last minute fixes and company directors are flying in from the US and Spain. You won’t believe what has brought about this excitement: Stevenage’s new Costco. 

 

It’s fair to say that new Costco outlets are not usually on RIBA Journal’s radar. There are 29 in the UK and the company, which is originally American, has been building nearly one a year for the past decade. But this one is different. Rather than commission its long-term architect Broadway Malyan to build yet another boxy store from scratch using a steel portal frame, two years ago Costco asked the practice to investigate the possibilities of taking on one of Stevenage’s most architecturally important and radical concrete buildings: the grade II listed, 15 x 8 bay hyperbolic para­boloid warehouse designed by Mexican architect Félix Candela Outeriño for John Lewis in 1963. The reasons for this decision remain a bit mysterious but are likely to do with the building’s prominent and car-accessible location. 

Seen from the roadside, Americanised in that Venturi-esque way with a huge angled billboard above the entrance and newly painted white, the building is bristling. Ten thousand Costco warehouse club members have joined before even getting a glimpse inside. And whereas refurbishments of listed buildings are often slow, this one was surprisingly uncomplicated and quick – though at 12 months rather than the usual 22 weeks, it’s still been shockingly long for Costco. A building that was previously private, designed for the turning circles of lorries and supply chain logistics, is now open to the public for a £28 annual membership fee. Ahead, all the bricked in ends and dock levellers have been stripped away to reveal a purist freestanding geometrical vision of the roofscape. The first third of this is now a vast car park canopy that’s ready for the burning heat of today and extreme rainfall and weather conditions of tomorrow. The rear, which incorporates some of the 1963 warehouse as well as a taller but otherwise identical 1970s addition, houses the store.

Félix Candela was born in Madrid in 1910 but after completing his studies emigrated to Mexico at the age of 26, a casualty of Franco’s regime. Santiago Calatrava is among those he taught, and in the Americas, where he spent much of his career, he is known particularly for the sense of geometry he applied to the design of thin-walled hyperbolic concrete shells. His subtle touches advanced the style and technical achievements of hyper architecture significantly. Although many of Candela’s curved structures seem to have no flat surfaces at all, his understanding of  shapes allowed him to cast them using straight pieces of wood, eliminating the need for expensive formwork. 

The Stevenage building is Candela’s only UK work and was completed with Yorke, Rosenberg and Mardall. Its 6.3m and 9.7m tall square concrete piers support slightly off-centre vaulted inverted pyramids, themselves connecting laterally but inclined to the north side, creating gaps for clerestorey windows that create a serrated roof profile. The daylight, stark on days like this, casts changing shadow shows on the shuttered concrete surfaces that make the shell concrete roof appear curved. 

 

Broadway Malyan’s brief was to come up with a pre-purchase plan for adaptive reuse of the warehouse, which remained in John Lewis’s ownership but was operating at 20% capacity after the partnership relocated its warehousing to more up to date facilities in Milton Keynes. The objective was to repurpose the 155m x 142m building to accommodate Costco’s standard and much smaller 13,000m² template and layout. This was achieved by splitting the site into 45 bays of covered parking and 75 bays of shop floor, each bay about 175m². The project received planning in December 2017 and Costco bought the site roughly three months later.

‘Betterment in terms of performance was also the aim,’ explains Broadway Malyan project architect Chris James. 

The building was mostly in reasonable  condition – the benefit of having had a single owner over its 54-year history. On site, the architect’s first move was to reduce the built area to the original listed concrete vaulted frame. It demolished two ancillary offices, a storage facility and an incinerator as well as metal mezzanines, non-original suspended ceilings and ad hoc elements inside. The next step was to remove all the side curtain walls, except the rear western full-brick elevation, exposing the primary freestanding structure. The rear store, enclosed by new off-white corrugated Kingspan KS1000 cladding, is similar to Costco structures elsewhere.

Much of the focus was on the roof itself. Fortunately, the original lower section had been redone by John Lewis relatively recently and required only patch repairs, whereas the higher area was dilapidated, leaking and poorly performing with only 6mm thick cork insulation. The roof covering was consequently stripped back to concrete and prepared with 30mm thick high performance Protherm Quartum insulation board suitable for sloping surfaces and Sarnafil Lead Grey felt-backed membrane, which was applied using an adhesive hot weld system. The finished membrane has a dirt repellent lacquered top coat, is treated with fire retardants and has a life expectancy of 40 years. Drainage, which is carried through the centre of the columns, also had to be resolved across the roof as a lot of blockages had to be cleared.

On the underside of the roof, the structure and columns were also found to be in fair condition, mostly just requiring making good. The exception was an area of three bays that accommodated taller lorries at the southern east corner of the original 1963 structure, which had to be supported by a new white-painted steel frame because of its more precarious condition. Otherwise the main works involved painting the concrete all-over white, which had been started by John Lewis without proper listed building consent and was incomplete. 

Other major works involved the concrete floor, which was worn by heavy traffic. Broadway Malyan decided to pour a new topping slab – 200mm on the low-bay area and 120mm on the high-bay area, except where it had to be removed for refrigeration units. This new slab has helped resolve an 80mm level difference between floors as well as allowing flush thresholds throughout, an important aspect for the retail function.

 

The architect had intended to replace all glazing on the site, but cost and time savings became necessary after the discovery of significant amounts of asbestos added four weeks to the build programme, so only the single glazing in the retail area has been replaced with double glazing. Some panels have, however, also become services outlets, including 16 ventilation units and spandrel panels for pipework. Much of the plant machinery is hidden in the sunken parts of the hyper roof.

In the car park, the original single glazing has been retained but protected with an additional membrane. Artificial lighting is surface fixed in runs beneath the north lights – LED strips in the parking area, pendants above the shopping aisles inside. Likewise, a sprinkler system, needed because there is no compartmentalisation, is attached  to the underside of the concrete shell roof, serviced by two beautifully gleaming 9m tall water tanks outside.

Conversion of this warehouse has made it Costco’s most historically and architecturally important building in Britain and the company has, unexpectedly, done a service to Stevenage and to architecture. The project also shows a good retrofit can be done quickly and cost-effectively (£1,345/m²) with the right architect, client and mutual ambition. 

There are a few gripes. The new store cladding could have been made of sturdier stuff, but it does at least have a conceptual logic showing what is new and what is not. But overall the project is well resolved, sparkling as it is in the sunshine. It is impressive that Costco saw the opportunity in taking on such a project. We need more companies to do the same for similar historically significant buildings facing uncertain futures, particularly retail giants that have fallen back on building steel portal frame boxes over the past 20 years. It would change the urban edge experience immeasurably. 

The dual simplicity and complexity of the architecture, enhanced by Broadway Malyan’s interventions, make the building just the kind of place where I’d want to do my shopping, joining the many others voting with their feet. It’s tranquil, special and has, as James intended, a ‘wow factor’ as well as abundant practicality – but next time I’ll probably arrive by car.  

---

In numbers
£19.54m
total contract cost
14,429m²
GIFA
£1,354
cost per m² 
611
parking spaces