The building sector exerts huge pressure on the built and natural environment and despite significant efforts to minimise the consequences, the International Energy Agency submitted that, by 2050, emissions related to buildings could double. However, in the building sector, significant improvement in energy use and reduction in greenhouse gas emissions can be achieved, given the potential to do this at no cost, using new technology. Since most buildings that exist now will still exist in 2050, the greatest energy savings can be made through refurbishment. In the future, legislation on carbon usage, as well as innovative technologies and knowledge, will trigger aggressive emission reductions in buildings, and this will compel installers of retrofit options to consider embodied emissions in order to achieve the best-value retrofit plan.This book, in response to the growing environmental importance of retrofit options, describes the development of a powerful decision support system, detailing both theoretical and practical insights, for the evaluation of environmentally and economically optimal retrofit options for non-domestic buildings. The chapters within it discuss engineering, energy, environment and economics in the context of climate change and sustainability, while a methodological framework of a decision support system is used to analyse a range of building energy retrofit options. The theoretical developments provided in this book can be transferred to other industries beyond the built environment and will be useful to researchers, energy systems engineers, architects, building energy managers, supply chain and procurement managers, sustainability managers and policy makers.