Thats The Way

As soon as you arrive at The Way in Beswick, east Manchester, you are left in no doubt that this is quite a special housing scheme. Beyond a curved block at the street corner runs a sequence of monopitch zinc roofs with exaggerated overhangs all round. Windows are all large, some running from floor to ceiling, and instead of dreary brick walls, it is clad in a mix of natural larch boarding, terracotta tiles, zinc sheeting and white render.

Behind the vibrant, diverse and richly modelled architecture of Lovell’s new housing in east Manchester stands Kingspan’s standardised system of structurally insulated panels

Hardly visible at all, but no less special, is the off-site construction adopted by housebuilder Lovell. In fact, with a total of 550 dwellings for sale and rent, it is claimed to be the largest off-site housing project in the UK. Like most of the £60,000 houses selected by English Partnerships earlier this year, the houses at The Way are built using structural insulated panels for walls and roof. In addition, each house has its own individual combined heat and power generator and a mechanical ventilation system with inbuilt heat recovery. And each street block comes with a communal communications mast. With these and other features, the scheme has scored a “good” rating on the BRE’s EcoHomes sustainability assessment.

The Way’s inspiring Urban Design, eye-catching architecture, modern methods of construction and inherent sustainability have all been encouraged by New East Manchester, one of the UK’s first urban regeneration companies. Lovell won the bid for the site owned by New East Manchester largely on the strength of these attributes, and The Way is one of the first new-build housing schemes instigated by an urban regeneration company to reach completion.

Various off-site systems of manufacture were investigated by Lovell at the start of the project, including timber frame, steel frame and structural insulated panels. “We were looking for a method that would deliver multiple benefits for both the construction team and the end user,” says Graham Bellis, Lovell’s regeneration managing surveyor. “We therefore focused our test on the following criteria: architectural design, thermal performance, speed of build, weather dependence, interface with other trades, supply risk and health and safety.”

Kingspan’s TEK system of structural insulated panels (SIP) was selected because it scored well in all categories, according to Bellis. The TEK structural insulated panels take the form of two sheets of oriented strand board (OSB), between which is sandwiched a rigid core of urethane insulation. The sandwich panels are large and strong enough to be used as complete structural walls and roofs for houses without the need for additional reinforcement. They boast high thermal efficiency with a U-value of 0.2 W/m²K and low air leakage of 0.08 air changes per hour at normal air pressures. In addition, external walls, including cladding and internal linings, need be no thicker than 223 mm, some 170 mm less than a timber frame wall, resulting in larger internal floor areas.

Off-site manufacturing was stretched a bit too far by the curved walls, which were made up on site of vertical studwork, and by the extended roof overhangs, which were supported on exposed steel T-beams

To Lovell, it was TEK’s high thermal performance that was particularly impressive. Ian Finney, Lovell’s regional operations manager, relates how he was accosted by a resident just before Christmas, who told him that he had just switched on his central heating for the first time.

“SIP scored over timber frame in terms of simplicity,” continues Finney. “The panellised system allows you to get a watertight system up quickly so you can start working inside in the dry. We managed to get the shell for a block of five flats up in just 10 days, not including foundations.”

While Lovell was investigating structural systems, architect Bowker Sadler Partnership was drawing up its house type designs. But, according to director Paul Jeffrey, the adoption of the SIP system did not compromise the spacious living rooms with open staircases, large windows and oversailing roofs that were already part of the design. “Any amount of holes can be made in the panels, and these are reinforced with four-by-two [inch] timber posts,” he says, pointing to the abundance of large windows, some so wide they would have required a hefty lintel in a brick wall.

But if compromises were not needed on the architectural design, they were as far as the SIP panels themselves were concerned. The eaves, which overhang by as much as 1200 mm, needed to be supported on steel T-sections exposed on the underside.

Other adaptations to the TEK system are less conspicuous. The system demands tolerances of just +/-2 mm over entire wall or roof panels, and these are particularly hard to achieve at the corners of conventional strip foundations. So Lovell devised a system of precast concrete ground beams for each wall that would be rag-bolted to piled foundations and adjusted to the precise level specified. A damp-proof course was then laid on top of the precast ground beam and the SIP panels erected on top of that.

Lovell accepts that the off-site SIP system is more expensive than conventional construction. The stylish architectural design and New East Manchester’s insistence that all dwellings should be accessible to disabled people, which added an extra 10-15% to floor areas, also added to costs.

In the site mock-up, a TEK structurally insulated panel stands on a precast concrete ground beam that provides precise tolerances and is clad in both render and terracotta tiles

So according to Tim Rackham, Lovell’s managing surveyor, Beswick houses were built for £750-915/m2 above DPC level, compared with £430-475/m2 for the company’s standard house types. “But this is offset by reduced construction time, less damage to elements exposed to the weather and a higher architectural quality, resulting in higher revenue from sales,” he says. “All the units in the first phase have been sold, and we have achieved the same level of margin as in our other housing developments.”

The micro-CHP units and the mechanical ventilation with heat recovery system can both be more accurately classed as environmentally sustainable features than off-site construction. The micro-CHP units were manufactured by WhisperGen of New Zealand and supplied by energy supplier Powergen, which claims it is the first such system in the UK. It provides heating and hot water just like a gas-powered boiler, but it also recycles the excess heat to generate electricity. Powergen reckons it can save each household up to £150 in cash and 1.5 tonnes in carbon dioxide emissions every year.

The mechanical ventilation with heat recovery system was supplied by Nu-aire and sits in a box measuring 500 × 350 × 200 mm in the roof space above the upstairs bathroom. A continuously operating fan extracts air from bathroom and kitchen and draws in fresh air through a vent in the external wall. A heat exchanger transfers heat from the exhaust air to the incoming air. The MVHR system means that no opening windows are needed in the house – a distinctive advantage for houses fronting a busy main road, as they are in Beswick, albeit one that is disconcerting to many new residents.