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Growth in the green house

Structures Sustainable buildings

Britain's first ever large-scale carbonneutral housing scheme is taking shape in south London. Mark Hansford finds out how new housing needs can be met without degrading the environment.

Environmentally friendly housing is nothing new.

Around the UK there are many examples of small, one-off projects using sound sustainable principles. However, a scheme in Beddington, south London, is about to launch energy efficient and environmentally sound housing into the big league.

Beddington Zero Energy Development - BedZed - will be Britain's first large scale high density housing scheme to truly integrate the latest thinking on sustainable development through the whole life cycle.

Eighty two homes and 1,600m 2of commercial space will be squeezed onto a 1.4ha former sewage works. Power will be produced onsite by a combined heat and power unit capable of providing 350,000kWh per year, fuelled entirely by waste trees.

All waste water will be fed through a 'living machine' which will treat the water to river water standards before recycling back into toilets and irrigation systems. All structural timber and 90% of structural steelwork used is re-used. Roads and pavements use the latest in 'porous paving'. There is even space for eco-friendly photovoltaic cells.

But the key to the scheme is in applying building physics concepts such as thermal analysis, passive cooling and ventilation and energy grading, ideas all in common use in the commercial office industry, explains services engineer Arup project director Chris Twinn.

'The basic principles are the same, ' he says. 'We store solar heat gain as energy to offset the heat losses of the house. It puzzles me why some people cover their buildings with photovoltaic panels in the name of energy efficiency and still only achieve a saving of 10% on total energy demand.

'Not every kilowatt is equal, ' Twinn continues. 'It is 100 times cheaper to get a kilowatt through a window than through a photovoltaic cell. The trick is to match building energy needs with energy availability, yet this principle is largely ignored by the housing industry whose answer to energy efficiency is to flog heat pumps at the home buyer's expense.'

Everything at BedZed is designed with the building physics concept firmly in mind.

The six three-storey terraces have south facing living spaces, with full-length windows to maximise the solar gain. This, combined with triple glazing, 300mm thick rock wool insulation, concrete floors for thermal mass damping, and a heat exchanger on a wind-driven ventilation system that recovers between 50% and 70% of heat from outgoing air, has - in theory - completely eliminated the need for further heat inputs.

'The key point is that the internal temperature does not drop below 19infinityC at any time, even if it is below zero outside, ' says Twinn. 'We have a heating cylinder for hot water, passive ventilation and a heat recovery system. But it is critical that we do not allow cold air to get into the building.'

And it is cost effective too, explains Twinn. 'It is a step change in design. If you can eliminate a heat cost then you can justify 300mm insulation and triple glazing. But it does mean you have to put a lot of effort in at the start of the project, which is when clients don't want to pay you.'

With solar power providing all the building's heating needs, power requirements are significantly reduced and, vitally, vary little throughout the year. This makes the constant output of an on-site biofuel combined heat and power plant not just environmentally sustainable but cost effective too.

At BedZed, the biofuel is chipped urban tree waste, a material that local authorities have in abundance and are desperate to dispose of in a way that avoids costly landfill taxes.

Supplied free of charge, the tree waste provides hot water and electricity to the low energy lighting and appliances used in the development. By avoiding fossil fuels in the process, BedZed can claim to have zero net carbon emissions, making it truly 'carbon-neutral'.

After two years of planning, work began on site in May 2000.

Construction is now nearing completion, on target for the December deadline, and the homes are selling fast. Of the 82 one, two, three and four bedroom flats and houses, 30% are for local authority-nominated affordable rent and 30% for shared ownership. The rest are for outright private sale at market value. With a 60% reduction in conventional energy demand and a 90% reduction in heat demand, this makes an attractive prospect for buyers.

While design and construction time has been significantly longer than would be expected for a normal 82 home development, this will improve as the team moves along the learning curve, claims Twinn.

What is really critical is the fact that in terms of overall structural cost BedZed is little different to a conventional structure, explains Jonathan Deans, construction manager and Gardiner & Theobald partner. 'The build cost for BedZed works out at £950/m 2. For similar high density residential schemes the construction cost will vary from £650/m 2to £1200/m 2depending on location and the type of units for sale.'

'We have shown that sustainable construction does not cost more and is a market driven solution, ' says Deans. 'It also shows that sustainable construction based on the units designed for BedZed offers a better quality of lifestyle, significantly lower running costs, and a real contribution to reducing global warming.'

Who s who Client: Peabody Trust Environmental consultant: BioRegional Architect: Bill Dunster Architects Structural engineer: Ellis & Moore Services engineer: Arup Construction manager: Gardiner & Theobold

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