Life Cycle Assessment in Sustainable Construction Projects

Life cycle assessment (LCA) in sustainable construction projects is governed by two complementary regulatory frameworks: standards ISO 14040:2006 (Environmental management — Life cycle assessment — Principles and framework) and ISO 14044:2006 (Requirements and guidelines) define the general LCA methodology in 4 phases (goal and scope definition, inventory analysis, impact assessment, and interpretation); standard EN 15978:2011 adapts this methodology to the building sector, defining modules A1-A5, B1-B7, C1-C4, and D as the accounting system for environmental impact throughout the building's life.

The functional unit in a building LCA is typically defined as 1 m2 of usable floor area over a reference period of 50-60 years (standard service life per EN 15978). The life cycle inventory (LCI) quantifies all input flows (energy, raw materials, water) and output flows (emissions to air, water, solid waste) associated with each module. The most widely used LCI databases are: Ecoinvent v3.9 (>18,000 datasets, global academic reference, Switzerland), GaBi (Sphera, >15,000 datasets, strong in European industry), and ELCD (European Life Cycle Database, representative data of European industry, European Commission). The access cost for Ecoinvent is 3,200-4,800 CHF/year for commercial use.

Standard EN 15804:2012+A2:2019 (EPDs for construction products) defines the mandatory impact categories for Environmental Product Declarations (EPDs): GWP (Global Warming Potential, kgCO2eq) quantifying the contribution to global warming; ODP (Ozone Depletion Potential, kgCFC-11eq) measuring ozone layer destruction; AP (Acidification Potential, kgSO2eq); EP (Eutrophication Potential, kgPO4 3-eq); POCP (Photochemical Ozone Creation Potential, kgC2H4eq); and ADP (Abiotic Depletion Potential) for mineral resources and fossil fuels.

The GWP indicator is the most widely used in practice: a conventional office building with a reinforced concrete structure has a GWP of 400-600 kgCO2eq/m2 in modules A1-A3 (embodied carbon) and 1,500-2,500 kgCO2eq/m2 in module B6 (operational energy over 50 years). EPDs are third-party verified documents declaring the environmental impact of a construction product per EN 15804. As of 2024, more than 90,000 EPDs have been published through programmes such as EPD International (Sweden), IBU (Germany), GlobalEPD (Spain, managed by AENOR), and INIES (France). The One Click LCA database integrates more than 150,000 EPDs from 70+ countries.

Building-specific LCA tools simplify the complex process of inventory calculation and impact assessment. One Click LCA (Finland) is the market-leading platform: intuitive web interface, direct BIM integration with Revit (automatic quantity import from the model), automated calculation of LEED v4.1 credits (MR: Building Life-Cycle Impact Reduction) and BREEAM credits (Mat 01), and a cost of 2,000-8,000 EUR/year depending on project volume. Tally (Building Transparency, USA) is a Revit plugin that calculates LCA directly from the BIM model using the GaBi database, optimised for the North American market.

For academic use and budget-constrained projects, OpenLCA (GreenDelta, Germany) is a free, open-source platform compatible with Ecoinvent and ELCD. SimaPro (PRe Sustainability, Netherlands) is the benchmark in academic research with over 25 years of development, a cost of 10,000-15,000 EUR/perpetual licence, and Monte Carlo uncertainty analysis capability. In Spain, the free tool eLCA from Germany's BBSR and the Unified Tool LIDER-CALENER (HULC) from the CTE calculate energy demand but do not perform full LCA. The BEDEC database from ITeC (Catalonia) provides environmental data for Spanish construction products usable in LCA.

The LEED v4.1 BD+C certification awards up to 3 points under the credit MR: Building Life-Cycle Impact Reduction for demonstrating, through LCA, a reduction in environmental impact compared to a reference building: option 1 (Whole Building LCA) requires modelling the complete structure and envelope with an LCA conforming to ISO 14044, comparing against a reference building with the same function and demonstrating minimum reductions of 10% in GWP and 10% in at least 2 additional categories (ODP, AP, EP, POCP, ADP). The reference period is 60 years.

BREEAM NC v6.1 is more demanding in LCA requirements: the credit Mat 01 (Environmental impacts from construction products) awards up to 6 points (of 12 available in the Materials category) for performing a whole-building LCA conforming to EN 15978 and demonstrating that the 15 products with the greatest GWP contribution have a verified EPD conforming to EN 15804. Scoring levels are based on performance percentile against a benchmark: 10% improvement in GWP over the benchmark (3 points), 20% improvement (5 points), 30% improvement (6 points). The EU Taxonomy (Regulation EU 2020/852) requires calculation of life cycle GWP for new buildings over 5,000 m2 as a criterion for substantial contribution to the climate change mitigation objective.

Comparative LCA studies demonstrate the impact of design decisions. A meta-analysis by Rock et al. (2020) of 238 buildings with published LCAs found that: buildings with engineered timber structures (CLT/Glulam) have a GWP in modules A1-A3 that is 25-50% lower than equivalent buildings with reinforced concrete structures; the variability of GWP among buildings of the same typology spans a factor of 3-5x, indicating a wide margin for improvement through design decisions; and operational carbon (B6) continues to dominate the life cycle in 70% of the cases studied, but its relative weight decreases with each improvement in energy efficiency.

In Spain, the LifeCycle Building project (funded by the EU LIFE programme, 2019-2023) performed full LCAs of 12 residential and office buildings, documenting a mean GWP of 450 kgCO2eq/m2 in modules A1-A3 for conventional reinforced concrete structures and 280 kgCO2eq/m2 for mixed concrete-timber structures. The use of concrete with 30% cement replacement by blast furnace slag reduces the GWP of A1-A3 by 20-25%. The combination of timber structure + Passivhaus envelope + photovoltaics reduces the total life cycle GWP (A-C, 50 years) to 600-900 kgCO2eq/m2, compared to 2,500-3,500 kgCO2eq/m2 for an equivalent conventional building: a reduction of 65-75%.