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The earth鈥檚 natural resources are being used 25% faster than the planet can renew them. Today, zero carbon is the centrepiece of the sustainability agenda, with the government signalling a major change in its attitude towards green and sustainable housing. In the UK 44% of CO2 emissions stems from the built environment. More than 20 million tonnes of CO2 could be avoided each year if the country鈥檚 homes were brought up to advanced energy saving standards and built to low carbon emission standards.

The government has announced that all new homes should achieve zero carbon emissions by 2016. Incentives have been proposed, including exemption from Stamp Duty for new homes. The government had previously announced grants of 拢50m for public sector and charity organisation projects in addition to the 拢28.5m (including 拢12.7m for householders) provided via the Low Carbon 好色先生TVs Programme.

Trade and industry secretary Alistair Darling鈥檚 confirmation of plans for two major offshore wind farms in the Thames Estuary that could generate enough energy for 750,000 homes is indicative of a readiness to embrace large-scale projects. But the real battleground is new homes.

Defining 鈥榸ero carbon鈥�

There is no agreement as to what exactly zero carbon means and it will take some time for a single definition to emerge. Conflicting debates concerning carbon neutrality and zero carbon, carbon emissions and energy generation and other issues, all need to be resolved while the accelerating pace of technological advances E E continues to challenge opinion and expand options. We use this working definition: 鈥淎 zero carbon house has zero emissions of carbon dioxide from all energy use in the home鈥� 鈥� this definition is similar to that given in the mayor of London鈥檚 energy strategy in Towards Zero Carbon Developments: Supportive Information for Boroughs: 鈥淗ighly energy-efficient developments, powered and heated by renewables with zero net carbon emissions.鈥�

Recently, Radio 4 defined a zero carbon house as one that 鈥渆xports more energy than it imports鈥� 鈥� a statement that actually defines carbon neutrality. In addition, the fact remains that incorporation of zero carbon technologies actually still results in carbon emissions and the embodied energy involved in the manufacture and transportation of renewables should be incorporated into the calculations. Similarly, biomass fuel can only be termed as carbon neutral as it emits the same amount of carbon as it ingests throughout its life.

Energy vs carbon

Another fundamental question is whether we should use a building鈥檚 carbon emissions or its energy outlay to assess the quantity of renewable technologies we latch onto the structure. Our view, although others may disagree judging by the variety of definitions in circulation, is that carbon emissions rather than energy demand should be used to set the appropriate target for the following reasons:

鈥� The new Part L Minimum Standards of the 好色先生TV Regulations assesses energy performance in relation to carbon emissions in that the Dwellings Emission Rate (DER) must be less than a Target Emissions Rate (TER).

鈥� The measurement of a building鈥檚 carbon emissions fits with the ethos of the energy white paper to reduce CO2 by 60% below 1990 levels by 2050.

鈥� Using carbon emissions rather than energy demand to assess the quantity of renewable technologies to be latched onto a building, recognises the fact that grid electricity is more carbon intensive than mains gas. (A typical three-bedroom house requires about 17,000kWh of energy per year, regardless of fuel. This means that to provide 10% of energy demand through renewable technology would be the same regardless of the fuel. Occupants are not deterred from using a more carbon-intensive fuel to supply the remaining 90% of energy demand).

In terms of carbon, however, gas produces 4,500kg of CO2 to heat the same house. Electricity would produce 7,000kg. This is due to the carbon-intensive generation of electricity through the burning of oil, the lost energy through cabling to the building and other heat losses along the supply chain. The carbon emissions per kWhpa is therefore as follows:

Elec energy = 1kWhpa = 0.42kg of CO₂ pa

Gas energy = 1kWhpa = 0.26kg of CO₂ pa

The outcome is that more renewables are required if a house is heated with electricity than with gas. This acts as a deterrent to the use of electricity for heating, which is cheaper to install than gas heating. Electricity is also more expensive for the end user and is becoming increasingly so, which may lead to further cases of fuel poverty.

The financial implications

An average zero carbon home will cost about 拢25,000 more to construct due to the higher initial capital cost. Although this cost will produce a long-term return (10 years plus, depending on the technologies used), the financial impact will be different for the private and public sectors. A private developer has greater financial flexibility to offset the additional costs and purchasers will be cushioned by the removal of Stamp Duty. The public sector is under immediate financial pressure and often, because of funding parameters, the lowest cost option is seen as the only possible way forward.

We have developed financial models to demonstrate long-term savings to encourage public sector clients to take the longer-term view. We also maintain a database of grants available to subsidise systems providing energy from renewable resources together with a database of suppliers of renewable technologies in order to provide some economies of scale. It should not be forgotten that existing stock is a prime generator of carbon emissions and yet VAT is currently charged on refurbishment projects but not new construction.

Conclusion

Climate change, rising energy prices and new environmental legislation have all played a part in focusing our minds on renewable technology. Before we choose our preferred sustainable energy source, we have to reduce the energy requirements of our buildings through, for example, increased insulation, passive stack ventilation and/or passive solar gains. By reducing the electrical and heating demand of a dwelling, the proportion of the energy requirement to be met by renewable energy will also be reduced and cost less to include.