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Specifier's choice:New East Manchester, Beswick

Sutherland Lyall talks to Bowker Sadler Partnership director Paul Jeffrey and project architect Mark Alston about the use of prefabrication and CHP units at a housing development for Lovell in the rundown Berwick district of east Manchester

Two years ago, architect Bowker Sadler Partnership teamed up with house developer Lovell to pitch for a 1,100-dwelling regeneration project also containing schools, shops and other social infrastructure, in the rundown Beswick district of east Manchester. With the decision down to two candidates - the other being a consortium centred on Gleesons - the client decided to split the project area and use both developers, allocating 550 homes to each. Lovell is currently on site with 176 units. It is about to submit another 234 for approval and the final phase will be for 150 dwellings. This is a project with great possibilities because there is the potential for developing 10 times this number of dwellings in the area and Lovell is on the local developer panel.

The site was originally masterplanned by PRP Architects, and the Lovell section is on a corner site. The layout is based on a segment of a circle whose centre contains public facilities. A major road arcs the middle of the site, with a parallel subsidiary road to the south.

There are three unusual things about this housing. First, it is not in the customary neo-vernacular or neo-this-or-that style.

Second, it is built using timber frame - more accurately, the Kingspan TEK prefabricated panel system, with steel framing bolted on the front to support cantilevering balconies.

The third is that the design is really, rather than possibly, sustainable and represents a first in the use of home-scale CHP (combined heat and power) units.

Block party Bowker Sadler director Paul Jeffrey explains the 12 house types: 'We have designed [the houses] as a series of blocks, in an interesting and quite complex way, rather than plonking standard plans randomly around the site. The aspiration from an early stage was to develop the design with a city-centre style vibrancy.

The centre of Manchester has recently gone through a great change, and we think this shouldn't be restricted. We wanted to be identifiably modern and Lovell thought it was a good idea because the site is 15 minutes walk from the centre of Manchester.

'We took the designs out to the local community as we were looking at 25 to 26 per cent affordable housing, which will be of the same house type as the for-sale units, and is scattered around the site.' Local consultation went on for more than a year. 'Naturally some people liked the whole idea and others said they didn't look enough like traditional houses, ' says Jeffrey.

Project architect Mark Alston says: 'We aimed to get away from the idea of the terrace, to break down the roofscape to a human scale.'

Lovell is also the main contractor so this is a kind of design and build contract. The relationship between Lovell and the architect is based on a letter of appointment.

'We are appointed as its design and build architect, ' says Jeffrey. 'We don't have a formal supervisory role, although we do the usual inspection job, and in some respects we have taken that a little bit further. Some contractors don't like the architect on site but Lovell is paying us to maintain a site presence to keep up the quality.' In fact, Alston runs a weekly all-day Wednesday meeting with current subcontractors to iron out any on-site difficulties.

Jeffrey is very comfortable with his builder client: 'Lovell has been very keen to give us a free rein. It has been a fantastic client and said it wanted to stretch the boundaries of what was possible. It said 'don't be restricted'. So there has been very little change from a cost perspective, and the first two or three blocks on site are exactly the same as in the drawings.' The 30-strong practice uses AutoCAD and has a couple of people in-house who do three-dimensional visualisations based on the industry standard program, plus the usual Photoshop and associated rendering applications.

Because of the number of houses involved, the architect asked for a lot of mock-ups from subcontractors. 'Because of the nature of the project, we had to get it right from day one, ' says Jeffrey.

As an example, Alston explains: 'With the steelwork it was very important to get the cantilevers and the slenderness right. The Steel Workshop set up mock-ups for us.' So did a number of other subcontractors, and Jeffrey takes the view that this was a good example of how partnering can work to everybody's advantage.

When the solution was not mock-ups, it was extensive research and lateral thinking.

For example, the architect decided to use the same source for all the roofing, rainwater goods and some metal cladding to privacy panels on balconies. Lovell had no direct experience of Rheinzink but the architect had.

'We are now working with Longworths [Longworth Building Services, an approved Rheinzink installer], ' says Jeffrey. 'It developed samples for us and there was a lot of involvement - it did all the copings and all the details associated with the roof, including gutters and downpipes. Having everything done by the same outfit means there is continuity and no split liabilities.' Some roof overhangs, mainly over bays, are in Sika Trocal. 'Trocal and Sarnafil are equally good single-ply membrane roofing systems and here it came down to price, ' says Jeffrey.

And the panel says? 'We looked at all kinds of construction systems. We developed a scoring system based on benefits and the Kingspan TEK structural insulated panel (SIP) came out on top.

Lovell had already used it for 20 houses on a small infill site to the north of Manchester - although it had used brick and tile cladding.'

Now Beswick represents the biggest deployment of the system in the UK. It is a Lantac (Local Authority National Type Approval) system-approved product of 140mm-thick storey-height panels comprising rigid urethane foam sandwiched between two 12mm sheets of orientated strand board (OSB). The insulation is very sticky before it is foamed and it is used to bond panels, core and perimeter frame during manufacture - also known as auto-adhesive bonding.

The resulting panels have a U-value of 0.2 for walls and roofs, well inside current Part L regulations. Joints between panels are sealed and achieve 1m 3/hr/m 2 where the Building Regulations ask for only 10m 3 per hour.

The panel system can be used for both walls and roofs - and with some span restrictions, for floors. At Beswick it was decided to use conventional floor construction with joists sitting in hangers hooked over the tops of the external storey-height panels. 'Panels are designed to fit in with the designs architects put forward, ' says Jeffrey. 'The data was taken from the CAD drawing, then the panels were laser-cut in Germany and brought over to the UK. It all started off with our suggestion that panel height should be around 2.4m, but it became apparent that you can vary the height to suit transportation limits. The TGI floor joists span the full width of each house - the plans all have a lot of open space.'

Up against the wall Walling materials, especially at ground-floor level, include terracotta rainscreen from Moeding Alphaton and thin-joint brickwork from Hanson. There is a lot of render.

'We went through a lot of discussions about rendering, ' says Alston. 'We put forward Sto to begin with but then we developed the design with the German render manufacturer Alsecco, partly because we wanted very sharp edges. The installer is another German firm, W Wunder, which is doing a lot of work in London; we wanted to make sure we had a firm that could do mock-ups locally.' Windows are white uPVC, which 'doesn't score brilliantly, but we have used it for a whole lot of reasons, ' says Jeffrey. 'There are maintenance problems with timber and public perception issues. We envisaged using it even in our original development sketches. We were interested in showing the glass rather than the frame, so windows are normally internally beaded. We have used Solaglas for the more difficult windows, where the spans are too big for uPVC, and for the curved structural glass balustrades and the bay windows.'

Interior elements Interiors are the final elements to be completed, so things such as wall tiling, flooring and decor are still being actively discussed. But Jeffrey's team has already developed a kitchen design to meet the budget with Yorkshire kitchen company Bluestone, and has done the same thing for wardrobes with Kelvin Kitchen, Bedroom & Bathroom Systems. Internal partitions are British Gypsum plasterboard fixed to that company's metal stud system.

Sustainable spaces 'We wanted to have big spaces and big windows, ' says Jeffrey. Big windows involved thinking about energy issues. 'We are having a lot of meetings discussing the problems of heat recovery using individual WhisperGen micro-CHP units from Powergen and the New Zealand firm Whisper Tech for each house. Because it produces electricity, it can be fed back into the grid. This is the first time this system has been deployed in a major housing development.'

The flexibility offered by large spaces could be accommodated by spanning floors from party wall to party wall. 'We wanted to have houses that were as open as possible so that people could use these homes as they wanted, 'says Jeffrey. 'We commissioned a fire engineer to take us through building control for agreement to using sprinklers.

For the three-storey houses we have open steel staircases with sprinklers from Homesafe Systems at each floor level.

'We've done an awful lot of development on ventilation and have worked closely with NuAire Home Ventilation, ' Jefferey explains.

'The general principle has been around for a long time: you pre-warm the air from the outside with the heat from outgoing air, and filter it before putting it into the main accommodation areas of a house. What we are trying to do is to get this system and the heating to work as a mini air-conditioning system. We are at the first step in such a process. It is a system a lot of developers are talking about but we are actually developing it.'

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