Green homes top agenda at Offsite2007

Some of the first houses designed to demonstrate compliance with the new Code for Sustainable Homes are to be unveiled at Offsite2007. While the first two Offsites in 2003 and 2005 were about showcasing prefabricated houses, this year the emphasis has shifted. Now, higher up the agenda than both speed of build and cost, sustainability and environmental impact have taken over as the principal drivers.

But is it possible to construct environmentally friendly buildings cost-effectively and strike a balance between sustainability and affordability? Research conducted by Cyril Sweett suggests that achieving level three of the Code for Sustainable Homes need not be prohibitively expensive. The cost consultancy found that the average additional cost would range from 0.4% to 6.2% more than achieving an EcoHomes 'Very Good' rating. Traditionally built detached and terraced houses were found to carry the highest premium while apartments and houses constructed using modern methods of construction were the cheapest.

Commenting on the results, Adam MacTavish, a director at Cyril Sweet, says: "While the costs of achieving these standards are high there are good reasons to expect actual costs to reduce as both the industry and its supply chain begin to focus on environmental performance."

Zero-carbon dwellings

Of the more ambitious, and costly, projects at Offsite2007, Stewart Milne and Kingspan Off-Site are aiming to demonstrate how they would conform to the top two levels of the code - level five and six respectively. This means that both dwellings will have to be as close to zero-carbon as possible.

Both buildings will feature renewable energy (a prerequisite in achieving code level four and above) to offset the carbon generated by the heating and lighting of the dwellings in use. Along with all the other demonstration homes, they will be evaluated by the BRE against the Code for Sustainable Homes. The BRE will provide a breakdown of the score and the actions taken to achieve it.

Kingspan Off-Site's two-bedroom LightHouse net-zero carbon home will have impressive levels of efficiency in terms of construction methods, energy use, CO2 emissions and carbon footprint. It is being designed in line with Lifetime Homes and Scheme Development Standards (SDS).

The house, built using Kingspan's TEK building system, will feature renewable technologies such as a biomass boiler and integrated photovoltaics in order for it to achieve the higher levels of the code. While the inclusion of these innovations will currently incur a prohibitive price premium, the house has been designed to be a blueprint from which a range of houses will be developed. This will allow the specification to be tuned to meet whatever level is required. "This development will be a launch-pad for us," explains Jonathan Jennings, R&D manager at Kingspan Off-site. "By achieving level six we will set a benchmark and then be able to scale it down to meet any other Code for Sustainable Homes requirements."

Chris Twinn, director of sustainability at Arup, concedes that achieving level six is currently difficult financially, but hopes the LightHouse will help the industry to understand what is required to achieve a zero-carbon home. "To achieve level six, contractors may experience some additional effort sourcing new products and suppliers, and developing new ways of working," he says. "In reality, there is an element of innovation cost you have to get over, but the work Kingspan is doing will be published and it will help others learn from its experience."

Commercial viability

The Stewart Milne Group is aiming to build a code level five house that is commercially viable. Again, the house will include superior insulation and renewable energy technologies, built around a timber frame building system. But Stewart Dalgarno, managing director at Stewart Milne, is also pragmatic when it comes to achieving the upper levels of the code. "We are building a vision of the future. What a house will look like in 2016," he explains. "There is some cost premium and the cost of renewable solutions is currently a significant part of this. However, this should reduce as the use of renewables increases. We are confident that with a community strategy to energy supply we can achieve levels five or six."

David Szymanski, managing director at Hanson Building Products, agrees that a community approach is vital if a financially realistic renewable energy strategy is to be achieved. "I think we should be looking at communities rather than house by house," he says.

"We need to look to the past, perhaps reintroducing district heating systems and focus on zero carbon communities rather than individual homes."

The Hanson House 2 project was initially devised as an entry into the Design for Manufacture competition that was launched by John Prescott at Offsite2005. "But we soon realised we should be looking towards energy efficiency," Szymanski explains. He says that the house was expensive to construct, but this was mainly down to its roof system (an affordable, simplified version will be available). The roof's design was inspired by a traditional brick kiln, utilising the 'stack effect' to ventilate the accommodation through a distinctive roof lantern. The lantern is 'intelligently' operated to open and close as required to meet the prevailing weather patterns, and so regulate internal air temperature. The unusual shape of the roof is further emphasised by vertically run zinc sheeting, with stack-bonded brickwork completing the building's distinctive appearance.

As in Hanson House 1, masonry panels manufactured offsite bring the benefits of speed of construction, while their high thermal mass creates a structure that copes with temperature extremes. As the house includes no renewable energy sources it will only reach level three of the Code for Sustainable Homes. "It doesn't matter how well you design the fabric of the house you will need to be using renewable energy to achieve a high eco home rating," Szymanski continues. "If you look at renewables, I see the sense in big wind turbines serving whole communities rather than relatively ineffective small-scale wind solutions. Ground-source heat pumps are another technology worth considering."

Like Hanson House 2, the Osborne Demonstration House was also conceived before the launch of the Code for Sustainable Homes. "The drivers for us were the new Building Regulations introduced in April 2006," explains Osborne director Paul Ensch. "We looked at the new regulations and wanted to see how much further we could push them." The structure of the house consists of Innovare Systems' structural insulated panel system (SIPS) and timber floor and roof cassettes. It features a number of different types of cladding, external finishes and internal features, so that visitors can get an idea of the range of options available.

Building Regs Part L

Carbon emissions for the house are 40% lower than required by Part L of the Building Regulations, and it is 10 times more airtight than the Regulations require. It needs two-thirds less energy for heating than a house constructed to 2006 Building Regulations, with total energy bills for the home estimated to be just £150 a year. "The question to crack is how to achieve that top-up of energy," Ensch continues. He says that Osborne is looking at a number of solutions to find what is affordable and realistic. "You must first reduce the demand in the fabric of the building. Once you have done that only then should you start looking at renewable energy. Technology such as mechanical heat recovery and solar thermal seem to me to be worthwhile, but I'm not so sure about photovoltaics."

Osbourne estimates that its demonstration house carries a cost premium of about £150/m2, which is relatively affordable considering the efficiencies it makes possible. The house is likely to achieve code level three, which would back up Cyril Sweett's research which suggests that gaining code level three will be up to 6% more expensive than achieving EcoHomes 'Very Good'.

The consensus is that it is going beyond that level that is currently prohibitively expensive, in the main due to the cost of renewable technology. As the Chartered Institute of Housing points out in its response to the consultation paper Building a Greener Future: Towards Zero Carbon Development: "The additional costs to achieve code level three seem to be relatively low.

"Although it is difficult to assess the likely cost of achieving higher levels of the code at this stage, the 'mass uptake' of micro renewable technology will certainly bring down prices in the medium to long term."

For more details visit: www.offsite2007.com

The Hanson House 2 (top left) is constructed using prefabricated masonry panels (bottom), while the Stewart Milne (top middle) and Kingspan Off-site houses (top right) are both constructed using timber frame.

School of thought

It is not just houses that feature at Offsite2007. Willmott Dixon is to create a school building with sustainability at the core of its design.

The company's consultancy, Re-Thinking, has joined forces with White Design, NG Bailey and Max Fordham to construct a 'school of the future' that will include a number of ideas to encourage the use of sustainable materials. While not being as large as a real school, Willmott Dixon says that it will demonstrate principles to be incorporated into a full-size school.

Built offsite using recycled timber supplied by Eurban, the school aims to emit zero carbon. Supplied to site flat-packed, the timber method does not require roof trusses or other projections that may inhibit expansion of the school.

As well as benefiting from a highly insulated envelope, the school will feature high levels of natural lighting. This will be supplied through a combined natural ventilation and a daylight 'chimney', which will demonstrate that it is possible to bring light into all classrooms, even in a three-storey school. Artificial light will be daylight linked.

For additional ventilation, windows and blinds will open automatically, allowing the school to 'breathe'.