Before renewable sources of energy are considered for any construction, consideration should first be given to ensuring maximum energy efficiency. In new construction, it is in theory possible to eliminate the need for external sources of heat, as for instance in the ‘passivhaus’ standard used in Germany and parts of Scandinavia. In practice, the most cost-effective solution to reducing energy use will often involve a combination of high insulation values in choice of material and design, together with appropriate forms of locally-generated renewable energy. The government has determined that by 2016, all new houses should be ‘carbon neutral’ or zero carbon. The definition of this (as set out in a consultation by the Department for Communities and Local Government (DCLG) in England in December 2008) is that such houses should: be built with high levels of energy efficiency; achieve at least a minimum level of carbon reductions through a combination of energy efficiency, onsite energy supply and/or (where relevant) directly connected low carbon or renewable heat; and choose from a range of (mainly offsite) solutions for tackling the remaining emissions. A recent report commissioned by the Department for Business, Enterprise and Regulatory Reform (BERR) for the Renewables Advisory Board concludes that, due to the electricity load created by appliances, renewables are essential to meet zero carbon standards – which in theory will be required for all new houses by 2016 – even where homes are constructed to the highest levels of energy efficiency. The report predicted very little demand for renewable energy in new homes before 2016, with the market for onsite renewables growing rapidly after that, and the highest level of uptake for biomass CHP and solar photovoltaics. It is worth bearing in mind though that as the rate of housing replacement is only about 4% of housing stock per year, the introduction of carbon free housing will have a limited effect in the short term towards achieving targets.

RENEWABLE ENERGY

For existing buildings, where it may not be possible or cost-effective to design in sufficient energy saving features, there will almost always be scope to reduce heat loss by measures such as double glazing and draught proofing. Wall, as well as ceiling insulation, will usually be a cost-effective option to be considered before installing renewable energy to support existing buildings. About one third of heat loss from a typical dwelling would be through the walls, and 15% through the roof.Wall cavities in homes built before 1990 will typically be un-insulated, and injecting insulation into the cavity will be a relatively low cost and highly cost effective option, costing perhaps £300 for a 3-bed semi-detached house. In very old houses with no wall cavity, wall insulation may have to be installed internally – where room size allows (if necessary, some insulation value can be derived from specially designed wallpapers without significant loss of space) or externally where this is compatible with the appearance of the building. Choice of construction materials may also have a major impact on the levels of embedded energy.