Life Cycle Assessment Basics

Overview

Life cycle assessment (LCA) quantifies environmental impacts from raw material extraction through manufacturing, transport, installation, use, maintenance, and end-of-life. In construction, embodied carbon in structure and envelope often dominates upfront emissions; operational energy dominates over decades two through fifty in typical commercial buildings.

Environmental Product Declarations (EPDs) standardize product-level LCA outputs under ISO 14025, but boundary choices, service life assumptions, biogenic carbon methods, and allocation rules can make two "comparable" numbers misleading. A lower GWP per kg might lose per m² of function if the product is thicker or replaces fewer conventional layers.

Building-level LCAs integrate assemblies, replacement cycles, and energy models. Product marketing that cites single-number carbon savings without functional units or system effects should be treated as hypotheses until modeled in context.

Key Principles

• Normalize comparisons with functional units (per m² wall, per MJ saved, per year of service).
• Distinguish cradle-to-gate, cradle-to-grave, and cradle-to-cradle boundaries on every data sheet.
• Document biogenic carbon treatment (storage, delayed emission, end-of-life scenario).
• Include maintenance, replacement, and transport in assembly-level totals—not product labels alone.
• Report uncertainty ranges when data is incomplete; transparent brackets beat false precision.

Embodied vs. Operational Carbon Tradeoffs

Highly insulated envelopes with foam or aerogel may raise embodied carbon while cutting decades of heating and cooling emissions. The breakeven year depends on grid carbon intensity, building lifespan, and whether refrigerant leakage is counted in operational models.

Dynamic materials—PCM plasters, phase-change roofs—need time-series simulation rather than steady-state R-value comparisons. LCA without operational coupling undervalues or overvalues these layers depending on climate file and occupancy schedule.

Common Pitfalls to Avoid

• Summing product GWP values with different declared units or system boundaries.
• Ignoring replacement intervals for finishes with short service life but low per-unit GWP.
• Double-counting biogenic storage in structure and again in corporate carbon inventories.

Put It Into Practice

• Pick one assembly and build a bill of materials with quantities from drawings.
• Gather EPDs or industry averages; convert to common functional unit before summing.
• Run a simple sensitivity analysis on lifespan ±10 years and grid decarbonization rates.
• Archive calculation spreadsheets for auditor review—screenshots of marketing claims are not enough.

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