Sat 1 Dec 2007
Hitting absolute zero
They are the buzzwords of the 21st-century but what exactly does zero-carbon mean, and how can it be achieved in housing? Roger Hunt reports. 
The government is legislating for it, the housebuilding industry is gearing up for it and the public are being wooed by it, but, when we strip away the hyperbole, the concept of the zero-carbon home is not quite as straightforward as it may appear. Nor is it necessarily as attainable or as 'green' as it first seems.There is general acceptance that we must act on climate change and, behind the principle of all new homes being zero-carbon by 2016, there is the very real need to limit emissions of carbon dioxide to the atmosphere. To put this into perspective, the country's 26 million homes are responsible for 27 per cent of carbon emissions and the UK has little hope of achieving its ambition of cutting greenhouse gas emissions by 60 per cent (from 1990 levels) by 2050 without bold initiatives.
As Nick Jones, head of housing best practice and low-carbon homes at BRE explains, the government aims to achieve the 2016 target through, among other things, a progressive tightening of regulations. "The primary measurement of energy efficiency for the Building Regulations is the Dwelling Carbon Dioxide Emissions Rate (DER) - an estimate of carbon dioxide emissions per square metre of floor area. Proposed revisions to the regulations in 2010 will require a 25 per cent improvement in the DER compared to 2006 levels, with a 44 per cent improvement in 2013 and finally, zero-carbon new homes in 2016."
Jones believes: "The Code for Sustainable Homes Levels 5 and 6 (the ultimate goal) present considerable challenges and raise many questions, including the fundamental ones of which carbon emissions are to be zero, what exactly we mean by 'zero' and whether offsite generation should be allowed."
'Zero' can be interpreted in a number of ways. These include zero-carbon: no carbon-emitting fuels are burnt on site and no electricity is imported from the grid. Net zero carbon: carbon emitting fuels are burnt on site, but locally generated renewable energy is exported to the grid to make up for this. Carbon neutral: off-site generated renewable energy is imported from the grid or via private wires.
The Code for Sustainable Homes Technical Guide, published by Communities and Local Government in October 2007, defines a "True Zero Carbon Dwelling" as being: "Where net carbon dioxide emissions resulting from ALL energy used in the dwelling are zero or better. This includes the energy consumed in the operation of the space heating/cooling and hot water systems, ventilation, all internal lighting, cooking and all electrical appliances. The calculation can take account of contributions from on-site renewable/low carbon installations. Off-site renewable contributions can only be used where these are directly supplied to the dwellings by private wire arrangement."
It is this last sentence which raises the most questions. In effect, it precludes the purchase of 'green' energy from the National Grid. A key issue with on-site generation is space, particularly in high-density urban developments, smaller sites and those in less windy parts of the country. Pooran Desai, sustainability director of eco-property development company, BioRegional Quintain, is far from convinced that generating all heat and power from renewables on-site is of value as a general policy, even though it retains its place in green aspiration and ideology.
"There is a role for on-site renewable energy generation, particularly for heating and hot water; for example, using solar thermal panels and wood-heating systems. However, when it comes to electricity generation there remain major issues with initial cost, long-term maintenance and operation. "Photovoltaic panels generate electricity reliably and with low maintenance, yet remain, and, for the medium term, are likely to remain, expensive for the amount of energy they generate. There are, as yet, no tried and tested small-scale biomass heat and power plants. If we want wind energy, we probably need to erect big turbines in windy locations."
Desai points to the fact that for a person living in a home built to current building regulations, heating our home now accounts for only about three per cent of carbon emissions while, for example, electrical appliances, hot water, waste and personal transport account for three per cent, four per cent, 13 per cent and 18 per cent respectively.
"If we consider other greenhouse gases like nitrous oxides and methane, not just carbon dioxide, up to one third of our impact comes from the production, processing and distribution of our food."
Consequently, the debate over zero carbon extends far beyond the performance of new buildings and indicates a more holistic approach is likely to be required. "We must build places where it is easy to lead an eco-friendly lifestyle - places where it is easy to walk and cycle, places which are far less car-dependent, where it is easy to recycle and where we have ready access to local, seasonal, organic produce," says Desai.
Taking these factors into consideration, BioRegional preceded most, if not all, organisations in coining the term zero-carbon, using it in the context of a "Z-squared - Zero Carbon Zero Waste community" concept. BioRegional defined zero-carbon as buildings run on a combination of on-site and new installed renewable capacity off-site, using fossil fuels only for back-up.
While a key objective is to reduce the carbon footprint of new homes, David Wood, Galliford Try's urban regeneration director, makes it clear that this also has to take account of the way in which energy is used by the people that occupy the homes. "There is very little point in creating a wonderful zero-carbon home and then have the occupants run it in a way that doesn't take full advantage of the technology and the initial design concept."
One of the problems that Wood identifies is that there are mixed messages. "There needs to be clarity from government about what it is trying to achieve. Obviously we would like the public to be in a position where perhaps they were prepared to pay a bit more for something that is of a greater quality and delivers a sustainable product for them as well as lower running costs".
Wood also believes that one thing the government might be able to assist in is collaboration in terms of R&D. "This is a turning point in terms of technology which we have never seen before so there has to be a greater collaboration."
The scale of the task facing housebuilders is illustrated by the comments of Peter Armfield, Linden Homes' technical director.
"Linden's homes are currently 40 per cent more energy efficient than Building Regulations require, but they will need to be 145 per cent more energy efficient in order to meet the new challenge. It is essential that the government assists with research into zero-carbon technology, if we are to achieve this transformation of new homes by 2016."
Simon Wright, chief executive of Simon Wright Homes and a member of the HBF's 'principle ten' steering group for London and the southern counties, continues this theme. "Developers have been advised to start looking into building elements that may provide quick and cost-effective high point wins.
"Research by Cyril Sweet for English Partnerships revealed the cost of building homes to Code for Sustainable Homes Level 5 could be as much £35,000 more than those designed to comply with 2006 Building Regulations."
At the BRE Innovation Park at Watford a number of 'real life' demonstration houses have been constructed with the aim of showing how modern construction and advanced technologies can come together to deliver low-carbon and sustainable homes.
Among them is a house, comprising two dwellings, built by Stewart Milne, which achieved Code for Sustainable Homes Level 5. The staircase is open-plan, helping to cool the building by using the stack effect to draw hot air up and out of a solar lantern on the roof. High levels of insulation and air tightness are features of the building, while solar hot water panels, photovoltaics and micro-wind turbines will reduce energy requirement to that needed for appliances only.
Jonathan Kingerlee, chairman of Kingerlee Homes, sees the current approach to combating carbon emissions in the UK's housing stock as "gimmicky" with not enough emphasis placed on the building's structure. "The government's plan to build zero-carbon homes is a commendable response to the need to improve the eco performance of our homes. However, by focusing on the creation of renewable energy, they are taking the attention away from the main issue - truly sustainable buildings, which require minimal energy to run."
At its Lincoln Grove scheme in Bladon, Oxfordshire, Kingerlee claims to have built to a specification that results in the properties produce less than half of the carbon emissions of traditionally built homes. In conjunction with Oxford Brookes University, it plans to monitor not only the gas, electricity and water consumption at Lincoln Grove, but also the temperatures and humidity within the rooms.
Kingerlee anticipates that "These results will demonstrate the need to build truly sustainable housing and highlight the flaws within the government's zero-carbon challenge."
First published in Show House Magazine December 2007.
The greatest care has been taken to ensure accuracy but some information contained within this article may have changed since it was first published.
Posted by Roger Hunt
in Sustainability on Sat 1 Dec 2007
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