Description This BRE Trust report considers the relative impact on UK CO₂ savings targets of constructing new zero-carbon buildings compared to improving the energy efficiency of the existing stock. Carbon dioxide emissions from buildings accounted for around 40% of total UK CO₂ emissions in 2006. To achieve the government's challenging target of reducing greenhouse gas emissions by 80% by 2050, improving the energy efficiency of buildings - both new and existing - will clearly be vital. This report uses existing data to explore the extent to which improving the energy efficiency of the existing building stock would be a more cost-effective route for achieving CO₂ savings than constructing new buildings to the higher levels of energy performance required to meet low- and zero-carbon targets. Contents Executive summary 1 Background Zero-carbon non-domestic buildings 2 Introduction 3 Assessing cost effectiveness Net annual cost Net present value 4 Domestic buildings Age profile of the domestic building stock Existing domestic buildings New domestic buildings Conclusions and recommendations: domestic buildings 5 Non-domestic buildings Non-domestic building energy and emissions model Age profile of the non-domestic building stock Existing non-domestic buildings New non-domestic buildings Conclusions and recommendations: non-domestic buildings 6 References A4, 32 pages.