Evaluating, benchmarking, and reducing embodied carbon of deep retrofit homes with significant extension: Irish case studies

Existing buildings contribute nearly 40 % of Europe's overall energy usage and represent about 36 % of the related greenhouse gas emissions from energy. Thus, the governments set retrofit targets for residential and non-residential buildings. The European Union has recently projected to transition from net-zero energy buildings to zero-carbon buildings by 2030, expanding the current building environmental performance standards to include embodied and operational carbon emissions. The study highlights the embodied carbon (EC) emissions linked to materials used in the deep retrofit measures for homes in Ireland. The research developed a novel methodology for evaluating the EC in deep retrofitted homes with defined benchmarks based on the results of the case studies. The findings show that the upfront and the whole-life EC averages of the deep retrofitted homes in Ireland are 347 and 662 kgCO2e/m2, respectively. These averages represent a benchmark for the current market practice and a starting point for developing EC reduction targets for upcoming projects. The study developed a methodology for reducing the EC of the retrofitted homes during the design stage through a group of material substitution scenarios for the most impactful materials in the case studies. Eleven materials were replaced with low-carbon alternatives available in the Irish market, resulting in an average of 23 % and 20 % reductions in the upfront and the whole-life EC emissions, respectively. Ultimately, the study is a guide for the retrofitting specialists to evaluate and compare the EC of their designs with the developed benchmarks, with solutions to achieve the reduction targets.