Environmental Product Declarations (EPD) and Embodied Carbon: EN 15804 Methodology Explained

An Environmental Product Declaration (EPD) documents the environmental impact of a construction product across its life cycle—from raw material extraction, manufacturing, and transport to site installation, through repair and maintenance to end of life and waste management. EPDs are produced by or on behalf of construction product manufacturers and serve as the primary data source for Whole Life Carbon Assessments (WLCA) of buildings and infrastructure projects.

EPDs are not certificates of quality or "organic labels." Instead, they provide standardised datasets that must be integrated into building- or infrastructure-level carbon assessments. The data comes from Life Cycle Assessment (LCA) methodology, which evaluates impacts against a range of environmental indicators. One of these indicators is global warming potential—commonly called embodied carbon. Crucially, an EPD does not measure carbon content as a mass; it assesses the impact of the product through the construction lifecycle.

What Does EN 15804 Define?

The European Standard EN 15804 sets out Product Category Rules (PCR) for the development of EPDs for construction products. The standard ensures that all types of construction products are assessed consistently using the same methodology and approaches. First published in 2012 and revised in 2019, EN 15804 has been refined by life cycle assessment experts over the years. The BSI convenes the UK Committee that contributes to and comments on the development of this European standard.

EN 15804 defines system boundaries and life cycle stages in a modular structure. The standard specifies which environmental indicators must be reported, how to model waste and recovery, and how to account for biogenic carbon content in materials such as timber or concrete.

How Is Embodied Carbon Assessed in an EPD?

Embodied carbon encompasses both CO₂ and other greenhouse gases. It includes emissions from all extraction, transport, and manufacturing processes required before products are ready at the factory gate for delivery to the customer—an assessment known as "cradle to gate." The scope can also extend to transport to site ("cradle to site"), installation impacts including construction waste ("cradle through construction"), maintenance such as cleaning, repairs, replacement and refurbishment, and end-of-life impacts such as demolition, recycling, and disposal.

When all life cycle stages are included, the assessment is termed "cradle to grave." This does not imply that products are landfilled; if products are typically recycled at end of life, a cradle-to-grave assessment accounts for this. The methodology follows ISO 14044 to ensure that the benefits of recycling are not double-counted for both the use of recycled content and recycling at end of life.

System Boundaries and Life Cycle Stages

EN 15804 structures the life cycle into defined modules, allowing specifiers and project teams to extract the data they need for specific stages. The modular approach means that a manufacturer can report cradle-to-gate data while still enabling downstream users to add transport, installation, or end-of-life data relevant to their project context.

System boundaries determine which processes are included or excluded. For example, capital goods, employee commuting, and overhead energy use at corporate offices are typically outside the product system boundary. Transport distances and installation methods vary by project and region, so EPDs often report these modules separately to enable project-specific customisation in whole life carbon assessments.

EPD Types and Comparability

EPDs can be product-specific (for a single manufacturer's product) or industry-average (representing a group of manufacturers or a sector). Product-specific EPDs offer greater granularity and can differentiate between competing products, while industry-average EPDs provide a benchmark when specific data is unavailable.

Comparability between EPDs is a technical challenge. Even when both are compliant with EN 15804, differences in system boundaries, allocation methods, data quality, and geographic scope can limit direct comparison. The Construction Products Association has produced technical briefing papers exploring comparability and uncertainty in EPDs, developed with contributions from Dr Jane Anderson, Chair of BSI's B/558 Committee, and Chris Foster, Chair of BSI's SES/1/5 Committee responsible for ISO Life Cycle Assessment standards.

EPDs and Whole Life Carbon Assessments in UK Projects

The UK was one of the first countries to recognise the significance of embodied energy in construction products. BRE published a national methodology for assessing cradle-to-grave environmental impacts with the Environmental Profiles Methodology in 1999. Based on this, the Green Guide to Housing Specification provided embodied assessments of over 200 building elements used in housing, which were incorporated into EcoHomes.

Today, EPD data feeds into whole life carbon assessments that increasingly influence design decisions and procurement. The London Plan requires Whole Life-Cycle Carbon assessments for referable planning applications. Other local authorities, such as Westminster, mandate WLC assessments for major redevelopment schemes involving substantial demolition. Tier 1 contractors now routinely request EPD data from subcontractors and suppliers as part of supply chain requirements.

Why EPDs Matter for Specifiers and Manufacturers

For architects, engineers, and project planners, EPDs enable evidence-based material selection that aligns with sustainability targets and circular economy principles. For manufacturers, EPDs demonstrate transparency and support competitive differentiation in a market where carbon performance is increasingly scrutinised.

EPDs are not static; they must be updated periodically to reflect changes in production processes, energy sources, or raw material composition. Verification by an independent third party is required under EN 15804, ensuring credibility and consistency across the industry.

More information on EPD methodology, system boundaries, and UK implementation is available from the Construction Products Association and ConstructionLCA infographics.