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Built to last: construction methods are changing so that our homes won’t cost the earth

Reporting on a domestic eco-revolution

By Gareth Chadwick
Saturday, 31 May 2008

Flower power: an artist's impression of The Orchid, an eco-house in the Cotswolds, recently sold for £7.2m [PA]

Head into any relatively Large town in the UK and you’ll see a skyline peppered with cranes, as developers work to meet the housing needs of our expanding population.

From the outside, many of these buildings look like their counterparts from 10 or 20 years ago, but thanks to a combination of regulatory demands and social expectations, virtually every home built today is kitted out with the kind of energy saving technology that, until recently, was the preserve of the eco eccentric.

Whether it is The Orchid, a revolutionary eco-house on a private estate in the Cotswolds which has sold off-plan for £7.2m, and which will have an underground heat pump, geothermal heating and cooling, rainwater collection and solar and wind power; or the low-cost affordable housing that is a key element of the giant Ebbsfleet Valley development in the Thames Gateway area of North Kent, innovative construction techniques are being implemented to create energy-efficient homes.

It is a much-needed effort. The energy footprint of the average home is relatively large. It is not only about the energy it uses once it’s complete, but also the energy used to create a building – its lifecycle assessment, which includes manufacturing components, extracting materials to make those components and transporting them from A to B, as well as the energy used in the physical building process, such as powering those cranes.

When it comes to creation, Kerry Mashford, head of sustainable manufacturing and construction at engineering consultancy Arup, believes passive design is key: “Passive design is about maximising the use of natural flows of heat, energy and light in order to minimise a building’s energy requirements. So, for example, it means planning the correct orientation of the building, taking account of the sun’s path. Designing roof overhangs to allow low winter sun in, while shading from high summer sun, means a home can be designed to need little – or even no – energy to keep it at a comfortable temperature all year round.”

The Government is promoting eco-construction with its compulsory Code For Sustainable Homes, implemented earlier this year to regulate the way new homes are built to be more sustainable. Regulating the house-builders is only part of the solution, however. Ian Arbon, senior partner at Engineered Solutions, believes the main challenges the industry faces are social, not technological, ones.

“People expect me as an engineer to come up with new technology that allows them to carry on living the way they do now. I’ve got bad news for them – they need to change their lifestyles. Solar and wind power are supply solutions, but we need a demand solution – and that means changing behaviour,” he says.

That those changes in behaviour are happening first in the construction industry is partly through the meticulous planning and innovation of mechanical engineers.

“Increasingly, we’ll reuse components and materials,” Mashford says. “Ideally, we should recycle into the same quality and performance as the original, rather than ‘down-cycling’ into lower grade materials. Our buildings must therefore be designed and built for future deconstruction.”

As well as considering how to re-use old construction materials, new cutting edge materials, such as phase-change materials (PCMs), are becoming increasingly common in today’s sustainable homes. PCMs are solid at room temperature, but when the temperature rises, they liquify and store heat, thus cooling the house. Conversely, when the temperature drops, the material will solidify and give off heat, warming the house. By incorporating PCMs in the building envelope, they absorb the higher exterior temperature during the day, and dissipate the heat to the interior at night when it’s cooler.

“It works like water freezing and thawing,” says Mashford. “Water at 0 degrees C contains a lot more energy than ice at the same temperature. We can use this process to store heat in the building fabric, enabling the building to absorb heat energy during the daytime without getting hotter, and then release energy when the air cools, maintaining the room’s temperature.”

These developments, Ian Arbon says, are all about flexibility: “I do my job well by resisting being pigeonholed as a mechanical engineer. It’s that fluidity which means architects and engineers are able to work together creatively to develop sustainable solutions for our homes.”

With all the technological advances stemming from mechanical engineering, the future could be one of zero-carbon housing. But in the meantime, there’s an enormous backlog of housing that is anything but energy-efficient, and improving the energy performance of existing houses is a key challenge.

One of the innovative technologies which could tackle the problem is micro combined heating and power (mCHP) – an appliance aimed at domestic use that provides heat and electricity simultaneously.

Paul Needley, joint managing director at energy consultancy Enertek International, explains: “Essentially, it’s a central heating boiler that produces electricity, which is either used in the property or sold back to the National Grid via a two-way meter.”

Not only are mCHP units set to offer significant carbon reductions, they will also offer an average annual saving per household of around £70, according to an independent report by the Carbon Trust. This saving could increase if the buyback rate paid by the electricity supplier is set at a competitive tariff.

You can’t rush out and buy one, though – the few hundred available are currently being used in field trials. Several units are scheduled to enter the UK market during the next couple of years, however, including one which Enertek is currently working on with its development partner, Disenco Energy.

The HomePowerPlant uses a so-called Stirling engine to drive a generator producing 3kW of electrical energy and 15kW of thermal energy. Amazingly, the Stirling engine was first developed almost 200 years ago, but it is only in recent years that its commercial use has been revived, thanks to the growing interest in mCHP appliances. The Stirling engine is ideal for domestic use due to its high efficiency, quietness and the ease with which its waste heat can be recovered.

“The technology is available and proven. The engineering challenge is to make it cost-effective, so adoption becomes widespread. The next generation will be grid in dependent units suitable for remote areas – it’s an exciting time to be working in this area of engineering,” says Needley.