Building Regulations Part L: Approved Document L1B Conservation of fuel and power in existing dwellings (2013 edition, effective 6 April 2014) requires a 25% improvement 2006 standards for every new home. An aggregate approach for improvement of new non-domestic buildings delivers an improvement of 25% overall, rather than for each individual building. This is because there is greater variety among non-domestic buildings and some will be much easier than others to make efficient. The changes to Part L increase the minimum levels of energy efficiency for building fabric and services, so that CO2 targets cannot be achieved through renewables alone. This reflects the principle of reducing overall demand for energy. The measures also come into play when people elect to carry out work to existing buildings including extensions and conversions, fabric renovations, replacement windows and boilers.