Environmental Product Declarations have become the currency of sustainable construction specification. As lifecycle assessment moves from academic exercise to regulatory requirement, architects and engineers need to read, interpret, and apply EPD data with confidence. For timber products — where biogenic carbon, renewable sourcing, and multiple end-of-life pathways create unique reporting complexities — understanding EPD methodology is essential for making defensible material selection decisions.
This guide explains how to read a timber EPD, what each section means, how to handle the biogenic carbon question, and how to apply EPD data in practice for whole-building assessments and green building certification.
What is an EPD?
Definition and Purpose
An Environmental Product Declaration (EPD) is a Type III environmental declaration per ISO 14025 that provides quantified environmental information about a product based on lifecycle assessment (LCA). It is:
- Standardised: follows EN 15804+A2 for construction products
- Verified: independently checked by a third-party verifier
- Published: registered with a programme operator (e.g., EPD International, IBU, BRE)
- Time-limited: valid for 5 years, then must be renewed
- Comparative: enables like-for-like comparison between products
EPD vs Other Environmental Labels
| Label Type | What It Tells You | Verification | Comparability |
|---|---|---|---|
| EPD (Type III) | Quantified lifecycle impacts | Third-party verified LCA | High (same PCR) |
| Eco-label (Type I) | Meets threshold criteria | Third-party certified | Limited (pass/fail) |
| Self-declaration (Type II) | Manufacturer's claims | Self-declared | None |
| Carbon footprint | GWP only | Variable | Moderate |
| FSC/PEFC | Sustainable forest management | Third-party audited | N/A (different scope) |
EPDs provide the most comprehensive and comparable environmental data, but they require technical knowledge to interpret correctly.
Structure of a Timber EPD
Standard Sections (per EN 15804+A2)
A compliant timber EPD contains:
- General information: manufacturer, product, programme operator, validity
- Product description: technical characteristics, composition, packaging
- LCA methodology: functional unit, system boundaries, data sources, allocation
- LCA results: environmental impact indicators by lifecycle module
- Additional information: scenarios, technical information, references
Functional Unit
The functional unit defines what is being assessed. Common functional units for timber:
| Product | Typical Functional Unit | Notes |
|---|---|---|
| Sawn timber | 1 m³ at 12% MC, planed | Specify dimensions and grade |
| Glulam | 1 m³ at 12% MC | Specify strength class |
| CLT | 1 m³ (or 1 m² at specified thickness) | Specify layer configuration |
| Timber frame wall | 1 m² of wall (specified U-value) | Includes all components |
| Decking | 1 m² installed (25-year service life) | Includes fixings and maintenance |
Critical for comparison: only compare EPDs with the same functional unit. Comparing 1 m³ of sawn timber with 1 m² of CLT panel is meaningless without conversion.
Lifecycle Modules Explained
Module Map
PRODUCT STAGE CONSTRUCTION USE STAGE END OF LIFE BEYOND
A1 A2 A3 A4 A5 B1-B7 C1 C2 C3 C4 D
Raw Transport Mfg Transport Install Maintenance Demo Trans Waste Disp Benefits
material to mfg Repair etc. to proc.
supply waste
Module A1: Raw Material Supply (Forestry)
For timber, A1 covers:
- Forest management (planting, tending, thinning, harvesting)
- Fuel for forestry machinery
- Fertiliser and pesticide application (if any)
- Forest road construction and maintenance
- Biogenic carbon uptake (negative GWP — carbon absorbed during growth)
Typical A1 GWP for softwood: −1,500 to −1,700 kgCO₂e/m³ (dominated by biogenic carbon uptake)
Module A2: Transport to Manufacturer
Covers transport of logs from forest to sawmill:
- Truck transport (typically 50–200 km in Scandinavia)
- Rail transport (where applicable)
- Ship transport (for imported logs)
Typical A2 GWP: 5–20 kgCO₂e/m³
Module A3: Manufacturing
For sawn timber, A3 covers:
- Debarking and sawing
- Kiln drying (largest energy input)
- Planing and finishing
- Preservative treatment (if applicable)
- Packaging
- Waste management (bark, sawdust, offcuts)
Typical A3 GWP: 20–60 kgCO₂e/m³ (highly dependent on energy source)
Key variable: sawmills using biomass energy (bark, sawdust) for kiln drying have significantly lower A3 impacts than those using fossil fuels. Scandinavian mills typically use 80–95% biomass energy.
Modules A4–A5: Construction Stage
- A4: transport from factory/warehouse to construction site
- A5: installation on site (cutting waste, energy for tools, waste disposal)
These modules are scenario-dependent — the EPD states assumptions about transport distance and installation method.
Modules B1–B7: Use Stage
| Module | Description | Relevance for Timber |
|---|---|---|
| B1 | Use (emissions during use) | Minimal for timber (some VOC release) |
| B2 | Maintenance | Surface treatment renewal (external timber) |
| B3 | Repair | Localised repairs |
| B4 | Replacement | Component replacement within building life |
| B5 | Refurbishment | Major renovation |
| B6 | Operational energy use | Not applicable to products |
| B7 | Operational water use | Not applicable to products |
For structural timber in protected conditions (service class 1–2), modules B1–B5 are typically zero or negligible. For external timber (cladding, decking), B2 (maintenance) can be significant.
Modules C1–C4: End of Life
| Module | Description | Timber Scenario |
|---|---|---|
| C1 | Deconstruction/demolition | Energy for removal |
| C2 | Transport to waste processing | Truck to recycling/energy plant |
| C3 | Waste processing | Chipping, sorting |
| C4 | Disposal | Landfill (if applicable) |
Biogenic carbon release: at end-of-life, the carbon stored in timber is released (combustion) or slowly released (landfill decomposition). This is reported as positive GWP in C3 or C4, balancing the negative value in A1.
Module D: Benefits Beyond System Boundary
Module D credits include:
- Energy recovery: timber combustion displacing fossil fuel electricity/heat
- Material recycling: timber chips displacing virgin wood in particleboard
- Reuse: avoided production of new timber products
Typical Module D GWP for timber: −200 to −600 kgCO₂e/m³ (significant credit)
Reading the Impact Categories
Core Environmental Indicators (EN 15804+A2)
| Indicator | Abbreviation | Unit | What It Measures |
|---|---|---|---|
| Global warming potential (fossil) | GWP-fossil | kgCO₂e | Climate change from fossil sources |
| Global warming potential (biogenic) | GWP-biogenic | kgCO₂e | Climate change from biogenic sources |
| Global warming potential (land use) | GWP-luluc | kgCO₂e | Climate change from land use change |
| Global warming potential (total) | GWP-total | kgCO₂e | Sum of all GWP components |
| Ozone depletion potential | ODP | kg CFC-11e | Stratospheric ozone damage |
| Acidification potential | AP | mol H+e | Acid rain, soil acidification |
| Eutrophication (freshwater) | EP-freshwater | kg PO₄e | Freshwater nutrient enrichment |
| Eutrophication (marine) | EP-marine | kg Ne | Marine nutrient enrichment |
| Eutrophication (terrestrial) | EP-terrestrial | mol Ne | Terrestrial nutrient enrichment |
| Photochemical ozone creation | POCP | kg NMVOCe | Smog formation |
| Abiotic depletion (minerals) | ADP-minerals | kg Sbe | Mineral resource depletion |
| Abiotic depletion (fossil) | ADP-fossil | MJ | Fossil fuel depletion |
| Water deprivation potential | WDP | m³ world eq. | Water scarcity contribution |
Typical Values for Timber Products (A1–A3)
| Indicator | Sawn Softwood (per m³) | Glulam (per m³) | CLT (per m³) |
|---|---|---|---|
| GWP-fossil | 30–80 kgCO₂e | 120–200 kgCO₂e | 150–250 kgCO₂e |
| GWP-biogenic | −700 to −850 kgCO₂e | −650 to −800 kgCO₂e | −650 to −800 kgCO₂e |
| GWP-total | −620 to −770 kgCO₂e | −450 to −680 kgCO₂e | −400 to −650 kgCO₂e |
| AP | 0.3–0.8 mol H+e | 0.5–1.2 mol H+e | 0.6–1.5 mol H+e |
| ADP-fossil | 400–900 MJ | 800–1,500 MJ | 900–1,800 MJ |
The Biogenic Carbon Question
The treatment of biogenic carbon is the most contentious aspect of timber EPDs:
EN 15804+A2 approach (current standard):
- A1: report biogenic carbon uptake as negative GWP-biogenic
- C3/C4: report biogenic carbon release as positive GWP-biogenic
- Net biogenic carbon over full lifecycle = 0 (carbon neutral assumption)
- GWP-total includes biogenic carbon (can make timber appear carbon-negative at A1–A3)
Practical implications:
- If only modules A1–A3 are reported: timber appears strongly carbon-negative
- If full lifecycle (A1–C4) is reported: biogenic carbon cancels out
- Module D can provide additional credit for energy recovery
Architect's guidance: for whole-building LCA, report GWP-fossil and GWP-biogenic separately. This provides transparency about both the processing emissions (fossil) and the temporary carbon storage benefit (biogenic).
Comparing Timber EPDs
Checklist for Fair Comparison
Before comparing two timber EPDs, verify:
| Check | Requirement | Why It Matters |
|---|---|---|
| EN 15804 version | Same version (A1 or A2) | Biogenic carbon reporting differs |
| Functional unit | Identical | Different units = incomparable |
| Declared modules | Same modules compared | A1–A3 vs A1–A5 is unfair |
| Product type | Same product category | Sawn ≠ glulam ≠ CLT |
| Moisture content | Same or normalised | Affects mass-based comparisons |
| Background database | Note differences | Ecoinvent vs GaBi can vary 10–20% |
| Energy source | Note differences | Biomass vs fossil dramatically affects A3 |
| Transport assumptions | Note differences | Affects A2 and A4 |
Example Comparison: Three Sawn Softwood EPDs
| Parameter | EPD A (Nordic mill) | EPD B (German mill) | EPD C (UK mill) |
|---|---|---|---|
| GWP-fossil (A1–A3) | 35 kgCO₂e/m³ | 65 kgCO₂e/m³ | 78 kgCO₂e/m³ |
| Energy source (drying) | 95% biomass | 70% biomass, 30% gas | 50% biomass, 50% gas |
| Transport A2 | 120 km truck | 80 km truck | 200 km truck |
| Electricity grid | Nordic (low carbon) | German (medium) | UK (medium-high) |
The 2× difference between EPD A and EPD C is primarily explained by energy source for kiln drying. This demonstrates why manufacturer-specific EPDs matter — generic industry averages mask significant variation.
Applying EPD Data in Practice
Whole-Building LCA
To calculate whole-building environmental impact using EPDs:
Step 1: Bill of materials
- List all timber products with quantities (m³ or kg)
- Include all structural timber, cladding, internal finishes, joinery
Step 2: Select EPDs
- Manufacturer-specific EPDs where available
- Generic/industry EPDs for early design stages
- Ensure consistent methodology across all products
Step 3: Calculate impacts
- For each product: quantity × EPD value per functional unit = product impact
- Sum across all products for each impact category
- Report per module (A1–A3, A4–A5, B, C, D separately)
Step 4: Normalise results
- Express per m² of gross internal floor area
- Express per year of design life (typically 50 or 60 years)
- Compare against benchmarks (RICS, LETI, RIBA targets)
Green Building Certification
| Certification | EPD Requirement | Credits Available |
|---|---|---|
| BREEAM (Mat 01) | Product-specific EPDs | Up to 5 credits |
| LEED (MR) | EPDs for 20+ products | 1–2 credits |
| DGNB | EPDs for LCA calculation | Required for certification |
| HQE | EPDs for environmental profile | Required for certain levels |
| WELL | Not directly required | Supports material transparency |
Carbon Targets and Benchmarks
Current industry benchmarks for embodied carbon (structure only, A1–A5):
| Benchmark | Target (kgCO₂e/m²) | Source |
|---|---|---|
| LETI 2020 target | < 350 | LETI Climate Emergency Guide |
| RIBA 2030 target | < 300 | RIBA 2030 Challenge |
| GLA (London) | < 500 (residential) | London Plan guidance |
| DGNB (Germany) | < 400 (office) | DGNB system |
| Typical timber building | 150–250 | Published case studies |
| Typical steel building | 350–500 | Published case studies |
| Typical concrete building | 400–600 | Published case studies |
Timber buildings typically meet even the most ambitious carbon targets without difficulty — the challenge is in foundations, services, and finishes rather than the timber structure itself.
Finding and Accessing EPDs
EPD Programme Operators
| Programme | Region | Database URL | Coverage |
|---|---|---|---|
| EPD International (Environdec) | Global | environdec.com | Extensive timber coverage |
| IBU | Germany/Europe | ibu-epd.com | Strong German manufacturers |
| BRE (EPD Hub) | UK/Europe | greenbooklive.com | UK-focused |
| INIES | France | inies.fr | French market |
| EPD Norge | Norway | epd-norge.no | Norwegian manufacturers |
| EPD Ireland | Ireland | igbc.ie | Irish market |
Generic vs Manufacturer-Specific EPDs
| Type | Accuracy | Availability | Use Case |
|---|---|---|---|
| Manufacturer-specific | High (±10%) | Limited | Final specification, certification |
| Industry-average (generic) | Moderate (±30%) | Good | Early design, feasibility |
| Worst-case (conservative) | Low (overestimates) | Always available | Screening, quick assessment |
For early design stages, generic EPDs from databases like Ecoinvent or One Click LCA are acceptable. For final specification and certification submissions, manufacturer-specific EPDs should be obtained from the actual supplier.
Future Developments
Regulatory Direction
- EU CPR revision: likely to require environmental declarations for all construction products
- EN 15804+A2 adoption: becoming mandatory across all programme operators
- Digital EPDs: machine-readable format (ILCD+EPD) enabling automated LCA
- Dynamic LCA: time-weighted carbon accounting recognising temporal storage benefits
- Scope expansion: increasing expectation to declare all modules (A1–D)
Implications for Timber
The regulatory trend strongly favours timber:
- Mandatory environmental reporting highlights timber's low-carbon advantage
- Biogenic carbon accounting (when properly applied) demonstrates storage benefit
- Circular economy metrics favour timber's multiple end-of-life pathways
- Renewable resource indicators favour timber over finite materials
For detailed carbon accounting methodology, see embodied carbon in timber and timber carbon footprint.
Related Resources
- Embodied Carbon in Timber — carbon accounting methodology
- Timber Carbon Footprint — lifecycle carbon analysis
- Net Zero Timber Buildings — achieving net zero with timber
- Timber vs Steel Environmental — material comparison
- FSC vs PEFC Certification — sustainability certification
- Sustainable Forestry Scandinavia — Nordic forest management
- Timber Recycling Circular — end-of-life pathways
- C24 Structural Construction Timber — structural timber products
- BSH Glued Laminated Beams — glulam products