A State of Play Review of Methods to Define Net Zero Carbon Buildings

Abstract

As time pressure rises to cut down greenhouse gas (GHG) emissions, countries have defined net-zero carbon targets for their buildings for 2050 or earlier. In practice, a wide range of definitions for net zero and related approaches to achieving these targets co-exist. This study is carried out by IEA EBC Annex 89 Subtask 2, dedicated to carbon accounting methods for buildings. Here, we use a classification matrix to examine national carbon accounting approaches used for buildings in Norway, Germany, the Netherlands, Canada, and the UK. We explore the definitions they express and analyze how aspects like the main fronts for carbon storage and offsets, carbon credits, secondary materials, benchmarks, and limit values are tackled. We also define negative emissions in line with the IPCC. All methods are bottom-up approaches, aligned closely with EN15978/15804. Some of them are mandatory, other voluntary but widely used. Not all methods model negative emissions materials; some that do so, misclassify the 'minuses' in the whole life carbon equation, regarding e.g. biogenic carbon, exported energy, and benefits beyond the reference study period. Of the methods examined, the UK's RICS PS is the only one that admits dynamic modelling (optional for reporting the benefits of carbon storage). Operational and embodied emissions are usually calculated, but not always coupled to provide whole-life carbon figures. The absence of benchmarks and limit values stresses the need to bridge the policy gap and link such methods to their countries emission reduction pathway.