Building within planetary boundaries: setting and assessing absolute sustainability targets at the building level

The planetary boundaries (PBs) are a widely used framework defining a “safe operating space” for environmental sustainability at the global level. However, they do not straightforwardly translate into indicators applicable in a building project. This paper proposes a procedure to set and assess absolute sustainability targets related to the PBs in a building project, exemplified in the case of Denmark. The first step is to ensure that the targets and the assessment method use comparable indicators. Common building life cycle assessment (LCA) tools use impact categories that do not directly match the PBs. Two options are considered to address this issue. Dedicated characterization factors can be used to convey LCA results in indicators consistent with the PBs. Alternatively, PB targets can be converted into LCA impact categories. Then, several distributive justice principles are reviewed to allocate a share of planetary sustainability targets to an individual country, to the housing sector within that country, and to an individual project. We argue that principles that conserve existing unsustainable paradigms are not appropriate to set planetary sustainability targets, and propose a novel approach for sectorial allocation based on sufficientarianism and “decent living” scenarios. Finally, challenges related to the assessment of these targets are highlighted. In particular, the paper draws attention to differences in system boundaries between the LCA and the targets.