Rogers Stirk Harbour + Partners (RSHP) may have had its fingers burnt with its previous foray into preassembled housing, but it is again championing such techniques at its new scheme in south London, writes Felix Mara
Following post-occupancy problems at the practice’s 2007 Oxley Woods housing development in Milton Keynes (AJ 15.05.14), some identified the root cause as its preassembly methods – or modern methods of construction (MMC). But the design logic for the architect’s Y:Cube Mitcham affordable flats argues that MMC is actually the solution to poor building performance.
The south London venture, which welcomes its first tenants this month, involves client YMCA London South West, RSHP and SIG Building Systems, which was responsible for off-site design and manufacture. The scheme tackles poor building performance on many levels, including capital and running costs. ‘In the end it was about economy,’ says RSHP director Ivan Harbour, ‘driving cost materials down, but for the right reasons.’
Tenants do not get exquisite architectural details on this budget
Y:Cube Mitcham is a C-shaped configuration of 36 short-term starter homes stacked around a central courtyard. It has been built for a remarkable £1.6 million, about a quarter of price of a one-bedroom flat in RSHP’s One Hyde Park in Knightsbridge. Tenants do not get exquisite architectural details on this budget, but for young people struggling to afford London rents or mortgage commitments, a studio in this charming little palace is something to aspire to, especially if the alternative is a bedsit or YMCA hostel. Its beach-hut-colour highlights and choppy skyline stand out against the sea of pebbledash terraces that surrounds it. ‘In a sense they’re a carrot,’ says YMCA London South West chief executive Richard James. ‘We can say to tenants in YMCA accommodation: if we feel you’re ready to move on and live independently, we’ll put you on the list for one of these schemes.’
The cost of development for this and other projected Y:Cube projects for YMCA London South West is critical because the target rent for the studios is 65 per cent of the equivalent on the local commercial market; low enough to qualify for housing allowances. In conjunction with low energy bills, this gives tenants the option to save money while training, working or studying, to enable them to live independently. Lower building costs also make it possible for Y:Cube developments to be constructed without capital funding and for outlay to be recovered from rent payments. Although the process is managed by YMCA London South West, half the tenants are local authority nominated. Unlike Oxley Woods, the Mitcham flats do not have owner-occupiers.
Y Cube by RSHP
RSHP suggested the Y:Cube idea as an approach to redeveloping YMCA London South West’s site in Wimbledon. The concept involves self-contained ‘plug-and-play’ factory-assembled accommodation modules which can be arrayed and stacked. Being lightweight and compact, they’re particularly suitable for awkward brownfield sites, which could be used to provide low-cost housing without building on green-belt land.
The Y:Cube combines RSHP’s longstanding interest in urbanism, housing and offsite fabrication. The practice previously designed a substantial but unbuilt unitised residential development for a Korean shipping company - the 1990-92 Industrialised Housing project. More recently, it was involved in the Homeshell project, which uses the Insulshell system developed by SIG and Coxbench, suitable for high-quality but fast-track and low-cost housing developments and other types of project. Homeshell premiered in the three-and-a-half-storey structure installed in 24 hours in the Royal Academy of Arts’ Annenberg Courtyard in London as part of its Richard Rogers exhibition in 2013.
It’s difficult to know what’s going on under the bonnet of the Y:Cube units, especially without seeing detailed drawings. ‘The manufacturer is quite secretive about how they go together,’ says Harbour. Presumably that’s because SIG wants to protect its intellectual property.
They’re actually no more cubes than the YMCA is exclusively for young male Christians. They are fully independent, using renewable engineered timber frames with all structural members in the external envelope zone. The outer cladding is cementitious board with visible mechanical fixings, apparently used as a rainscreen rather than as part of a sandwich, with sealants between the panels. Rather than gypsum board, the internal wall lining is magnesium oxide panels with pronounced joints, avoiding damage to internal finishes when transporting Cube modules to site or relocating them. Special jigs are used to lift the units, which have reinforcement around their lifting eyes. All these were assembled and tested in SIG’s factory in Alfreton, Derbyshire, and arrived on site fully finished.
RSHP’s vision was crucial to the project at all stages
RSHP was the concept designer, as at Oxley Woods, and SIG was responsible for the modules’ performance. ‘In a sense we are mere space planners,’ Harbour jests. Nevertheless, RSHP’s vision was crucial to the project at all stages, and it was involved in essential decisions such as over the proportions of the units, which were made longer after prototypes were scrutinised. Their width and height was constrained by transport restrictions. RSHP originally wanted all units to be identical, albeit with inclined ceilings on the top floor, but deferred to the planning authority’s view that ground-level units should have street entrances. There are also additional windows in end units, which are useful for surveillance and improve the quality of these flats.
On the street side, rainwater pipes as well as soil and vent stacks are enclosed by cementitious board columns in half relief, and these stop short of the matching barge boards. The colours of the balustrades to the wide access walkways match the doors and glow with inter-reflected light.
The thermal insulation and air infiltration of the units out-performs Approved Document L. Factory-assembly with tolerance of ±2mm helped to make this possible. Fan-assisted vents, which run continuously and are finished with smart silver grilles on the walkways, boost the airtightness and remove condensation. All this delivers all-electric heating with hot water bills of only £1 a week.
The modules, which have a design life of 60 years, cost £30,000-35,000 each – overall, Y:Cube Mitcham was about 25 per cent cheaper than traditional construction. As Harbour observes, refinement in the manufacturing process and SIG’s buying power helped to minimise costs and maximise quality. As short-stay flats, the units do not have to comply with GLA space standards or Lifetime Home standards, so the expense of a lift has been avoided. There are no disabled-accessible loos, although these could be installed. Below-ground construction was inexpensive because the modules are so light and structural framing is only required for the access deck and the staircase. ‘It’s probably a bit too industrial,’ says Harbour. ‘You can tell we’ve not been involved in it.’
He concludes that: ‘Trying to make something very quickly in a world that’s not used to it is very difficult.’ But Y:Cube has generated enormous interest from incipient partners. The rise of MMC seems inexorable despite a risk-averse construction industry – or perhaps because of it.