Meet the new kid on the modular housing block

Rational House – a concept that delivers homes in kit form to site – is bringing an integrated design, construction and manufacturing team to the market. Elaine Knutt reports.

Is this modular urban housing system likely to be a game-changer for Modern Methods of Construction? The integrated team behind Rational House is cautiously ambitious for their factory-to-site offering, which is about to be given its first full outing in an infill development of 10 houses planned for Hammersmith’s Spring Vale estate. With three other sites nearby under negotiation, also for the London Borough of Hammersmith & Fulham, there’s a confirmed pipeline of around 50 homes.

The design, construction and manufacturing team is cautious, because we all know that offsite housing’s new dawn has been sighted more times than an Indian summer – only for all the optimism to dissolve away to nothing. When brick-skinning a steel or timber frame is a cost-effective way of producing volume housing, why invest in a supply chain and production line doing something different? But it’s also ambitious, because Rational House has the backing of the Aecom brand — and it might just have launched at the right time.

Its target market is local authorities looking to develop their sites for either open market or discounted market sale, a tenure type suited to the so-called “squeezed middle”, where the council retains a variable slice of the equity. But the decisive factor is that local authorities can now draw on funds in their Housing Revenue Accounts, an opportunity likely to appeal to London and other authorities in the south east aware of the need to increase housing supply.

 

Rational House challenges the conventions on housing design and delivery methods

 

Rational House’s modular flexibility, speed of erection, and low impact on surrounding residents means it can exploit small infill sites overlooked by mainstream developers, offering cost certainty and a sliding scale of additional cost benefits related to the volume ordered.

Ben de Waal, head of residential at Aecom, explains: “We’re trying to deliver better living space for people, and offering a more diverse housing delivery option for the industry that embraces both new design principles and methods of delivery.

“Hammersmith & Fulham is to all intents and purposes the lead developer, they’re taking the risk, and at the moment we provide the supply chain, but come back in six months and we have a different [funding] model that reduces the funding and construction risk for the client,” he hints.

Ultimately, the ambition is to deliver more than 1,000 units a year by 2020, a level similar to Kier’s private housebuilding division Kier Homes. Probably this will involve tapping into Aecom’s expertise on masterplanning and delivering major sites, and possibly – as de Waal has hinted – it could also encompass taking on development risk.

Rational House is an urban housing “product” named in tribute to the underlying research that informed it: a study into successful urban housing in nine world cities by co-founder Bob Dalziel of 3D Reid. Factors identified include high daylight levels with large windows, open plan living spaces and high ceilings – a Rational House home has a 2.85m floor to ceiling height compared to the recommended 2.4m in the London Design guide.

 

A mock-up showing Fusion’s steel frame and Sterling’s panels

 

But, equally important, the homes have a solidity and permanence that the London streetscape needs, and can sometimes be missing in lightweight steel or timber-framed construction. “It suits the ambience of Hammersmith & Fulham, the product we’ve got sits comfortably in that environment,” says Rational House chairman and co-founder Tim Battle, formerly of services consultant Rybka Battle.

The product also answers a call for the “new London vernacular”: homes that draw on the proportion and street presence of much-loved Georgian and Victorian terraces but apply 21st century design and technology.

Multiple unit sizes

The system can be configured for flats in blocks up to 10 storeys, maisonettes, three-storey town houses, terraced or detached houses, and can accommodate multiple unit sizes to suit the site’s constraints. At Spring Vale (left), there will be eight flats and two three-bedroomed houses. Primarily seen as an urban product, the team also envisages it could be suitable for edge of city sites. With Aecom already acting as masterplanner for the vast North West Cambridge development, de Waal says Rational House is likely to submit a proposal.

However, in construction terms, Rational House isn’t particularly ground-breaking. It’s an MMC modular system, based around a library of pre-selected, mutually-compatible components that are available in a range of dimensions.
But rather than establishing a new manufacturing capability, Rational House has pulled existing companies into its supply chain: Fusion Building Systems is responsible for building and installing the structural frame, and Sterling Services manufactures and erects the concrete cladding panels.

Windows and doors are supplied by Nordan, and AST supplies the metal window shutters that gives Rational House a decidedly Continental feel. “In summer, you can close the shutters but keep the airflow, and they help with security – Secured by Design loves them,” notes Battle. There are also plans to extend the predetermined supply chain to encompass fit-out trades in future iterations – de Waal says they didn’t want to “nail” M&E and fit-out too soon.

Fusion’s lightweight steel gauge frame arrives pre-boarded with insulating infill to create the floors, load-bearing internal walls and roof, creating a watertight external envelope and removing the cladding installation from the critical path. Finally, the pitched roof is constructed from a lightweight steel frame, and covered with a zinc coating, although it’s not yet clear whether this would be applied in the factory or onsite.

Don’t mention the “c” word

The cladding system relies on 80-90 different panels for a typical house, hooked onto the frame. Joseph Cefai, founder director of precast specialist engineering firm Sterling Services, shies away from the “c” word. “We don’t want to talk about concrete, people think ‘grey’ and ‘prison’, so we call it architectural precast,” he says. The panels are made from a clay stent, taking on different colour tones according to the type of aggregate used: Spring Vale, for instance, uses three different cream and yellow tones. Cefai notes that there are no proprietary secrets in the panels – in future, any other supplier could replace or join Sterling in the supply chain. “But the ethos has been ‘we’ll invest in you if you invest in us’.”

At Spring Vale, the supply chain is responsible for the structural shell, but Willmott Dixon, as main contractor, is preparing the site and foundations, fitting out the shells and completing any external works.

For Spring Vale, Willmott Dixon has calculated a build time of 33 weeks compared to 45-46 weeks for a conventional build. 

The Rational House project is also allying BIM technology to MMC. Fusion, Sterling and other subcontractors contribute Revit-designed components to an integrated design model, which Aecom then links to the BIM Measure package to rapidly calculate detailed cost plans.

On cost comparisons versus traditional construction, Battle and de Waal first ask the question: “What is traditional construction?” “We get asked this all the time, and the answer is ‘it depends’. If you’re talking an industry-standard 2.5m from floor to floor family house with a conventional slate roof, or for brick and block flats with supporting steelwork, we’re probably more expensive,” acknowledges Battle.

But de Waal is quick to put that in context. “Much more so than with traditional build, with houses that embrace MMC the price is more connected to volume. With 10 homes, you’re not really generating the right level of pricing for MMC. But if we get an order for 1,000 units, we can go out to Sterling, Fusion and the supply chain with that certainty and they can price it in for perhaps 50% savings in construction cost.” The production timescale would of course also drop.

The team also points out that with the market recovering and talk of labour and material resources being stretched, their guaranteed supply chain and lower onsite labour costs could start to skew the cost analysis is their favour. “There’s a constant drive for fixed price contracting – contractors that can’t fix their costs increase their risks and that makes the product more expensive. But we can give clients certainty during the tendering process,” says de Waal. 

Hammersmith was certainly convinced by the Rational House proposition, aware of the need to create more middle-market housing in its increasingly polarised post codes. The borough was also keen to embrace new forms of technology and work with integrated supply chains. “Hammersmith & Fulham have been on the journey with us, but as people see Spring Vale go up, it’s possible that other London boroughs will be interested. But the last thing we want to do is go out and grow too quickly then fail because of supply chain delivery problems – that’s been a typical problem with MMC in the past,” notes de Waal.

Rational thinking leads to an integrated team

The Rational House story is quite complex. The intellectual property in the design originated with Tim Battle and architect Bob Dalziel, who established Rational House Ltd. Aware that the pages of the Architect’s Journal are full of architect-led modular housing systems that remain forever at prototype stage, the duo brought in Aecom and Willmott Dixon to advise on commercialisation, buildability and supply chain issues.

Rational House then licensed the design to a new company, City House Projects, which is now in contract with Hammersmith & Fulham council to provide design, planning and construction services. Dalziel and Battle retain a role in concept masterplanning the actual projects, but detailed design will be delivered by Aecom’s architects.

Battle, de Waal and Joseph Cefai are all keen to stress that Rational House is a team drawing on a wide spectrum of skills, experience and support, rather than ego-driven designers or messianic MMC flag-wavers. “Having been in the industry all my life, I’m determined this should be a collective endeavour,” says Battle.

“We’re working as a dedicated team, it’s not four separate companies asking ‘who’s responsible for this?’ or playing the blame game. With Revit as the integrator, the feeling is we’re one team,” concludes de Waal.