Life Cycle Assessment (LCA)

What is a lifecycle assessment and how does it differ from related terms?

A lifecycle assessment (LCA) is a standardized method for accounting for the environmental impacts of a building, product, or material across its entire life, from raw material extraction through end-of-life disposal or recycling. It is crucial to understand what LCA is not. LCA is the methodology itself, not a document. An Environmental Product Declaration (EPD) is a verified document that reports one product's LCA results. Global Warming Potential (GWP), typically expressed as kg CO2e, is one impact category within an LCA report. Whole-life carbon is a building-level figure that sums GWP across all lifecycle stages of a complete building. Confusing these four terms is common and leads to specification errors. You cannot ask a manufacturer for "an LCA"; instead, you ask for an EPD. You cannot optimize a building for LCA; rather, you optimize for one or more impact categories that LCA quantifies.

How is a building's lifecycle divided for assessment purposes?

LCA divides a building's or product's life into defined modules, each with specific boundaries. Modules A1-A3 cover the production stage: raw material extraction (A1), manufacturing (A2), and transport to the building site (A3). Module B encompasses the construction phase, the use phase (maintenance, repair, replacement parts over typically 50 years), and operational energy. Modules C1-C4 cover end-of-life: deconstruction, transport to processing, processing itself, and disposal or landfill. Module D is a separate account for benefits beyond the product boundary, capturing environmental credit or burden from recycling, energy recovery, or reuse of materials. Critically, many EPDs stop at A3 (cradle-to-gate assessment), meaning they declare only the emissions from extraction through manufacture and delivery to the factory gate, omitting all downstream stages. This is why you cannot compare a cradle-to-gate EPD to a cradle-to-grave one without adjusting scope.

Which standards define lifecycle assessment methodology?

LCA is governed by three layers of standards. ISO 14040 and ISO 14044 define the general methodology for any LCA: goal and scope, lifecycle inventory, impact assessment, and interpretation. EN 15804 applies ISO 14040-44 to product declarations. It defines how manufacturers must structure environmental product declarations for construction materials and components, ensuring EPDs are comparable within a common framework. EN 15978 applies the same principles at building level, establishing how to assess the environmental performance of whole buildings, including all lifecycle modules and defining the calculation rules for buildings in occupied scenarios. When you read an EPD or whole-building LCA report, it should declare which standard it follows and which product category rules (PCR) or calculation method were used.

Why has embodied carbon's share risen as buildings get more efficient?

In a typical 1980s house, operational energy for heating, cooling, and hot water accounts for 75-85% of total lifecycle emissions over 50 years. The remaining 15-25% is embodied carbon in materials and construction. As building envelopes improve with better insulation, triple glazing, heat recovery ventilation, and higher air tightness, operational emissions fall dramatically. A passive house with a heat demand below 15 kWh/m2a reduces operational impact by 80-90% compared to an average home, sometimes approaching zero in climates with decarbonized electricity. This shifts the carbon balance: embodied carbon may now represent 40-60% of the lifecycle impact. This reversal is why embodied carbon suddenly matters for designers of high-performance buildings. An LCA on a passive house reveals truths that an LCA on a conventional house does not: material selection, waste reduction, and durability now provide climate benefits equal to operational savings alone.

How do you interpret and compare LCA results?

An LCA report shows multiple impact categories: global warming potential in kg CO2e, acidification potential, eutrophication potential, water use in m3, and others. Most architects focus first on GWP because it dominates climate policy; however, optimizing for GWP alone can shift burden to other impacts. For example, sourcing a very low-carbon concrete through an unfamiliar supplier might reduce CO2e but increase water consumption or acidification. Holistic design considers the full profile. When comparing two LCAs of two materials, or two buildings, or two design options, ensure they share the same lifecycle scope, functional unit (per m2, per kg, per unit), assumed service life, end-of-life model, and reference year. A 2024 EPD and a 2018 EPD cannot be directly compared without verifying the background database and GWP factors used. Always ask for the LCA calculation details before drawing conclusions from the headline number.

What are the main limitations of lifecycle assessment data?

LCA is powerful but not perfect. Results are highly sensitive to assumptions: the chosen service life (is a window 30 or 50 years?), the end-of-life model (is that concrete recycled or landfilled?), the background database (ecoinvent vs. GaBi vs. industry-specific data), and the functional unit all shift outcomes by 20-50%. An EPD for insulation may assume 50 years of service, while an EPD for a window might assume 30, making direct comparison misleading. Generic data from public databases is often pessimistic because it averages many producers, including inefficient ones. A manufacturer's own EPD might show significantly lower impact, but this could reflect either genuine efficiency or cherry-picked production data. For materials without published EPDs, assumptions fill the gap, and different LCA practitioners make different assumptions. Two LCAs of the same building conducted independently can differ by 30-50% without either being wrong. For this reason, LCA is best used not to determine an absolute answer, but to compare options under consistent boundary assumptions and to identify which materials and lifecycle phases drive the largest impacts. In Slovakia, LCA is not a permit requirement for a family house, but it reaches projects indirectly through EPD specifications in large-scale green building certifications, through material selection drives by institutional developers, and through EU-level whole-life carbon reporting that will apply from 2028 onward for buildings over 1000 m2 and from 2030 for all new buildings. Understanding LCA limits and proper comparison method is essential as these requirements tighten.