Reading an Environmental Product Declaration for Building Materials

An environmental product declaration (EPD) is an independently verified document that reports the environmental impacts of a building product over its life cycle, such as its embodied carbon, measured with a common method so that products can be assessed in a building life-cycle assessment. EPDs are most useful for comparing products of the same type and for whole-building carbon calculations; their main drawback is that numbers are only comparable when they follow the same rules and declared unit. This guide is for architects and students: it explains what an EPD contains, how to read its tables, a worked comparison, where EPDs help and where they mislead, and the checks to make before you rely on one.

Quick answer: what an EPD is, best uses and main drawbacks

• What it is: a “Type III” environmental declaration under ISO 14025:2006, based on a life-cycle assessment (LCA) carried out to product category rules (PCR). For construction products in Europe the core PCR is EN 15804:2012+A2:2019; internationally, ISO 21930:2017 plays a similar role. An independent verifier checks the LCA and the EPD is published by a programme operator.
• Best uses: choosing between similar products (for example two concrete mixes or two insulation boards) on carbon and other impacts; supplying data for a whole-building LCA; meeting procurement or certification requirements.
• Main drawbacks: EPDs report per declared unit, not per building element; results depend on the modules declared; and products are only comparable within the same PCR, standard version and building context.

The anatomy of an EPD

Most construction EPDs follow the same structure: general information, product description, LCA rules, results tables and verification. The parts to read first are the declared unit, the system boundary (which life-cycle modules are included), the results table and the validity and verification details.

Declared unit and functional unit

The declared unit is the quantity the results refer to: 1 m³ of concrete, 1 tonne of steel, 1 m² of insulation at a stated thermal resistance. A functional unit goes further and describes a function over a time, such as “1 m² of wall with a U-value of 0.18 W/m²K for 60 years”. Comparing products only makes sense once you convert their declared units to the same function in your building: 1 m³ of a lightweight block and 1 m³ of a dense block do not do the same job.

Life-cycle modules

EN 15804 divides a product’s life into modules. The table summarises them. Under the 2019 revision (A2), EPDs for most products must declare A1-A3, C1-C4 and D; earlier EPDs often declared only A1-A3 (“cradle to gate”).

Indicators: more than one carbon number

EN 15804+A2 splits global warming potential (GWP, in kg CO₂-equivalent) into GWP-fossil, GWP-biogenic (carbon taken up and released by biomass, such as timber) and GWP-luluc (land use and land-use change), which together make GWP-total. Results under A2 and the older A1 version should not be mixed in one calculation. For timber products, A1-A3 often shows a negative GWP-biogenic value because the wood stores carbon; that carbon is released again in end-of-life modules C3-C4 if the wood is burned or decays, so always read A and C together (One Click LCA help: EN 15804+A2 indicators).

Other indicators include acidification, eutrophication, ozone depletion, resource use, water use and waste. They matter for a full assessment, though carbon is usually the focus in early design.

A worked comparison

Suppose you are choosing a concrete mix for a 25 m² ground-floor slab, 200 mm thick (5 m³). Two ready-mix suppliers offer EPDs for C30/37 concrete. The figures below are illustrative, not from real EPDs:

Mix B saves 400 kg CO₂e for this slab, about 29%. Before choosing it, check that both EPDs use the same PCR and EN 15804 version, the same declared unit and strength class, and similar data years; that Mix B meets the structural and durability specification (cement replacements can slow early strength gain); and whether the EPDs are product-specific or industry averages. An EPD does not tell you whether you need 5 m³ in the first place: a thinner slab or a different structural solution may save more.

Where EPDs help and where they mislead

Where they help

• Comparing like with like: two insulation boards of the same thermal resistance, two steel sections from different mills, two concrete mixes of the same class.
• Whole-building LCA to EN 15978 (Europe) or comparable methods, where EPD data replace generic database values.
• Procurement: the Buy Clean California Act, for example, requires EPDs for structural steel, concrete reinforcing steel, flat glass and mineral wool board insulation on state-funded projects, and sets maximum GWP limits that products must meet (California Department of General Services).
• Certification: schemes such as LEED and BREEAM award credits for using products with EPDs.

Where they mislead

• Different declared units (per m³ versus per tonne versus per m²).
• Different system boundaries: a cradle-to-gate EPD compared with a cradle-to-grave one.
• Different PCRs or standard versions (EN 15804+A1 versus +A2, or EN 15804 versus ISO 21930).
• Industry-average versus product-specific EPDs: an average hides the spread between manufacturers.
• Module D benefits (such as future recycling) reported as if they were certain savings today; most methods report D separately.
• Expired EPDs: EPDs are normally valid for five years, after which the data may no longer reflect production.

Checklist before you rely on an EPD

1. Is it third-party verified and published by a recognised programme operator?
2. Which standard and version (EN 15804+A2, ISO 21930) and which PCR?
3. Is it product-specific, manufacturer-average or industry-average?
4. What is the declared unit, and how will you convert it to your building element?
5. Which modules are declared? Are A1-A3 and C1-C4 both present?
6. Is it still valid? Check the issue and expiry dates.
7. For bio-based products, are GWP-fossil and GWP-biogenic reported separately?
8. Does the product still meet the technical specification (strength, fire, durability) for your use?

Maintenance, lifespan and cost factors

An EPD describes the product at the time of the study. Use-stage modules (B1-B7) depend on assumptions about service life and maintenance, which may not match your project. In a building LCA, set the service life of each product for your project (for example a 60-year reference study period for the building) and count replacements explicitly. EPDs are usually free to download from programme operators’ libraries; producing one costs a manufacturer the LCA study, verification and registration, which is one reason smaller manufacturers may only have industry-average EPDs. Costs vary by country and programme, so they are not quoted here.

Decision summary

Use an environmental product declaration to compare products of the same type on the same basis and to feed a whole-building carbon assessment, not as a label on its own. Convert declared units to your building element, check the standard version, modules and validity, and remember that design decisions such as using less material often save more carbon than switching products. For wider context, see our introduction to what is sustainable architecture, our overview of sustainable products and materials, and examples of bio-based hempcrete buildings.

Sources and further reading

• ISO 14025:2006, Environmental labels and declarations: Type III environmental declarations.
• EN 15804:2012+A2:2019, Sustainability of construction works: Environmental product declarations: Core rules for the product category of construction products (CEN, Europe).
• ISO 21930:2017, Sustainability in buildings and civil engineering works: Core rules for environmental product declarations of construction products and services.
• One Click LCA: EN 15804+A2 indicators.
• California DGS: Buy Clean California Act.
• The International EPD System: EPD library.