Development of a Life Cycle Assessment Allocation Approach for Circular Economy in the Built Environment

TLDR

Transitioning the built environment to a circular economy requires metrics, and life cycle assessment can evaluate environmental performance, but conventional LCA focuses on individual products and single life cycles, whereas circular assessment demands a systems perspective that accounts for multiple uses and life cycles of buildings, components, and materials. The study aims to determine how to allocate benefits and burdens between life cycles and to develop a circular economy linearly degressive approach that better aligns with CE principles and incentivizes industry adoption. The authors compare four LCA allocation approaches—EN 15804/15978 cut‑off, Circular Footprint Formula, 50:50, and linearly degressive—and calculate environmental impacts for four circular building components (concrete column, timber column, recyclable roof felt, and window with reusable frame). The study found notable differences in impact distributions among the allocation approaches, with the linearly degressive approach showing promise for both open and closed‑loop systems, and the newly developed CE LD approach further aligning with circular economy principles.

Abstract

Transitioning the built environment to a circular economy (CE) is vital to achieve sustainability goals but requires metrics. Life cycle assessment (LCA) can analyse the environmental performance of CE. However, conventional LCA methods assess individual products and single life cycles whereas circular assessment requires a systems perspective as buildings, components and materials potentially have multiple use and life cycles. How should benefits and burdens be allocated between life cycles? This study compares four different LCA allocation approaches: (a) the EN 15804/15978 cut-off approach, (b) the Circular Footprint Formula (CFF), (c) the 50:50 approach, and (d) the linearly degressive (LD) approach. The environmental impacts of four ‘circular building components’ is calculated: (1) a concrete column and (2) a timber column both designed for direct reuse, (3) a recyclable roof felt and (4) a window with a reusable frame. Notable differences in impact distributions between the allocation approaches were found, thus incentivising different CE principles. The LD approach was found to be promising for open and closed-loop systems within a closed loop supply chain (such as the ones assessed here). A CE LD approach was developed to enhance the LD approach’s applicability, to closer align it with the CE concept, and to create an incentive for CE in the industry.