Materials
Life-Cycle Assessment
LCA
A standardized method for tallying a product's environmental impacts across defined stages of its life. Results depend entirely on the system boundary and assumptions declared, which is why two studies can disagree.
In more detail
Life-cycle assessment is a standardized method for tallying the environmental impacts of a product or building across defined stages of its life — raw material extraction, manufacturing, transport, installation, use, maintenance and end of life. ISO 14040 and 14044 set the framework: define a goal and scope, build an inventory of inputs and outputs, assess impacts, interpret.
Results depend on declarations made before any calculation. The functional unit fixes what is being compared — a square metre of flooring over sixty years is a different question from a kilogram of material. The system boundary fixes which stages count: cradle-to-gate covers production only, cradle-to-grave includes use and disposal. Allocation rules decide how impacts are divided when one process yields several products.
That is why two credible assessments of the same product can disagree. The variation usually lives in the boundary, the assumed service life, the electricity mix assumed for manufacturing, and the end-of-life scenario. Comparing results without comparing those assumptions is the most common error in using the method.
Why it matters
LCA is the machinery behind every embodied carbon figure and every environmental product declaration, which makes it the reason those numbers are comparable in some situations and not in others. For a homeowner it explains how a material can be presented as the low-impact choice by one source and not another without either being dishonest — and it identifies the question that resolves it: what boundary and service life were assumed?
The common misunderstanding
That LCA produces a single environmental score. It produces results across multiple impact categories — global warming potential, acidification, eutrophication, resource depletion — which frequently point in different directions. Collapsing them into one number requires weighting choices that are value judgments rather than measurements.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.