5. EPD Modules Explained: What Do A1-A3, B, C, and D Mean?

When you open an EPD, the first thing you’ll notice is how environmental impacts are organised into alphabetic modules rather than being presented as single totals. This modular structure isn’t arbitrary. It serves specific purposes that make EPDs useful for building assessment and product comparison.

The modules represent distinct life cycle stages from raw material extraction through manufacturing, use, and disposal. Each module captures impacts occurring at that stage. This disaggregation lets you see where impacts occur, compare products stage by stage, and aggregate data for whole building calculations.

Understanding what goes into each module transforms EPD tables from confusing grids of numbers into information that tells you something meaningful about products and their environmental profiles.

Why Modules Exist: The Building Context#

EN 15804 designs EPDs as building blocks for whole-building environmental assessment. The modular structure ensures EPDs can be aggregated to calculate building-level impacts.

When architects and engineers assess a building’s life cycle environmental performance using standards like EN 15978, they need product data organised consistently. They take the A1-A3 modules from all the building materials to calculate production stage impacts. They take the B modules to calculate use stage impacts. They take the C modules for end-of-life impacts.

This aggregation only works if every product EPD uses the same modular structure. Insulation, concrete, steel, windows, and every other material must report impacts in the same modules covering the same boundaries. The standardised structure makes this possible.

The modules also support comparison in building context. You can’t fairly compare insulation products just by looking at their total life cycle impacts. One product might have higher manufacturing impacts but save more operational energy. The modular structure lets you compare manufacturing impacts (A1-A3) separately from use stage performance (B6 for operational energy) and understand the tradeoffs.

Module A: Product Stage (Cradle to Gate)#

Module A covers everything from raw material extraction through the factory gate. It’s subdivided into three sub-modules that trace material flows through the supply chain.

Module A1: Raw material supply captures impacts from extracting and processing raw materials up to the point they arrive at the manufacturer. For a concrete product, A1 includes:

• Limestone quarrying for cement production
• Clay and gypsum extraction for cement
• The cement manufacturing process itself
• Aggregate quarrying (sand, gravel, crushed stone)
• Any admixtures or supplementary materials

For manufactured products with complex supply chains, A1 can be the most data-intensive module. You need information from upstream suppliers about their processes, energy use, and material sources.

Module A2: Transport to manufacturer accounts for moving raw materials from suppliers to the manufacturer’s facility. This includes:

• Distance travelled by each material
• Transport mode (truck, rail, ship)
• Fuel consumption and associated emissions
• Return trips if relevant

A2 often represents a relatively small share of impacts unless materials come from distant sources or require energy-intensive transport modes. However, for heavy low-value materials, transport can become significant.

Module A3: Manufacturing covers the manufacturing process itself including:

• Energy consumption (electricity, natural gas, other fuels)
• Process emissions from chemical reactions (e.g., CO₂ from cement calcination)
• Water consumption
• Waste generation and treatment
• Packaging production
• On-site transportation and equipment operation

For energy-intensive products like steel, aluminium, glass, or cement, A3 typically dominates the product stage. For assembly products made from pre-manufactured components, A3 might be relatively small.

Module A1-A3 together represent the “cradle to gate” boundary that most EPDs have historically reported. Until recently, many EPDs stopped here. EN 15804+A2 now requires construction products to report modules beyond production.

What dominates Module A? For bulk materials (concrete, steel, glass), raw material processing and manufacturing energy drive impacts. For processed goods with refined materials, upstream supply chain impacts in A1 often exceed direct manufacturing impacts in A3. For products with minimal processing, A2 transport can be surprisingly significant relative to A3.

Module A4-A5: Construction Process Stage#

These optional modules cover getting the product to site and installing it.

Module A4: Transport to site accounts for moving finished products from the factory to the construction site. This is scenario-dependent because the manufacturer doesn’t know where products will be used.

EPDs must state assumptions: “Assumed average transport distance 500 km by truck.” Users can adjust scenarios for their specific projects if the actual distance differs significantly.

Module A5: Installation covers the construction process including:

• Energy for on-site equipment
• Water consumption during installation
• Material waste from cutting, trimming, or damage
• Auxiliary materials (fasteners, adhesives, sealants)
• Waste processing for installation scrap

A5 matters more for products requiring complex installation, auxiliary materials, or generating significant waste. Simple products with minimal installation requirements show low A5 impacts.

Most construction product EPDs report A4 and A5 based on typical scenarios. Manufacturers don’t usually have primary data for installation because it happens at job sites they don’t control.

Module B: Use Stage#

Module B subdivides into seven modules covering everything that happens while the product is in use. Not all modules apply to all products.

Module B1: Use covers direct impacts from the product’s presence in the building. For most construction products, this is zero. The product just sits there. For products that off-gas VOCs or require climate control, B1 might show impacts.

Module B2: Maintenance accounts for regular maintenance activities:

• Cleaning materials and water
• Energy for maintenance equipment
• Transport for maintenance personnel
• Waste from maintenance activities

Products requiring frequent maintenance (exterior coatings, certain finishes) show significant B2 impacts. Products requiring minimal maintenance show near zero.

Module B3: Repair covers less frequent interventions to restore function:

• Replacement of damaged sections
• Repair materials and components
• Energy and equipment for repair work
• Transport for repair materials

The boundary between maintenance and repair can be fuzzy. Generally, maintenance is routine and scheduled. Repair is responsive to damage or failure.

Module B4: Replacement addresses products or components with shorter life than the building:

• Full product environmental profile for replacement units
• Installation impacts for replacement
• End-of-life impacts for removed units

A product with 25-year lifespan in a 60-year building assessment requires replacement approximately twice. B4 would include environmental impacts from those replacement units.

Reference service life stated in the EPD determines B4 calculations at building level. A product claiming 60+ year life has zero B4 impacts. A product with 15-year life shows substantial B4 impacts from multiple replacements.

Module B5: Refurbishment covers major renovations affecting the product:

• Materials for refurbishment
• Energy and equipment for refurbishment work
• Waste from removed materials
• Transport for refurbishment materials

This differs from B4 replacement in that refurbishment is typically driven by building-wide renovations rather than product failure.

Module B6: Operational energy use captures energy consumed by the product or saved by the product during operation:

• Heating or cooling energy affected by thermal performance
• Electricity consumption for active systems
• Energy savings from improved building performance

B6 is where insulation shows huge benefits. High-performance insulation has higher A1-A3 manufacturing impacts but massive B6 operational energy savings that outweigh production impacts many times over.

For passive products, B6 reflects how thermal, acoustic, or other properties affect building operational energy. For active products (lighting, HVAC systems), B6 includes direct energy consumption.

Module B7: Operational water use accounts for water consumed by the product during operation. Most construction products show zero. Products like cooling systems or irrigation products might show B7 impacts.

What dominates Module B? For passive products with long life (structural materials, most construction products), B modules are often zero or minimal. For products affecting operational energy (insulation, windows, HVAC), B6 can dwarf all other modules. For products requiring regular replacement (finishes, membranes with limited life), B4 becomes significant.

Module C: End-of-Life Stage#

Module C covers everything that happens when the product is removed from the building.

Module C1: Deconstruction/demolition includes:

• Energy for demolition equipment
• Transport for demolition crews
• Water for dust suppression
• Separation and sorting activities

Selective deconstruction for material recovery requires more energy than bulk demolition. Products designed for easy disassembly reduce C1 impacts.

Module C2: Transport to disposal accounts for moving materials from site to disposal, recycling, or recovery facilities:

• Distance to disposal facilities
• Transport mode and fuel consumption
• Multiple trips if materials go to different facilities

Module C3: Waste processing covers treatment before final disposal:

• Sorting and separation
• Crushing, grinding, or size reduction
• Cleaning or decontamination
• Processing for recycling
• Incineration with or without energy recovery

C3 is where recycling activities appear. Steel sent for recycling shows impacts from collection, sorting, melting, and reprocessing. This module captures the burden of recycling processes, while the benefits appear in Module D.

Module C4: Disposal includes final disposal impacts:

• Landfill operations
• Methane generation from organic materials
• Leachate treatment
• Long-term monitoring and management

Products going to landfill show C4 impacts from site operations and long-term emissions. Products completely recycled show minimal C4. Products with mixed end-of-life (some recycled, some landfilled) show C4 proportional to the landfilled fraction.

Scenarios matter enormously for Module C. EPDs must state assumptions about end-of-life treatment: “Assumed 70% recycling, 30% landfill based on current UK practice.” If actual recycling rates differ, real impacts will differ from the EPD.

Countries with high recycling infrastructure show lower C modules than regions with limited recycling. This makes international comparison tricky because end-of-life scenarios reflect different infrastructure.

Module D: Benefits and Loads Beyond the System Boundary#

Module D is the most controversial part of the EPD structure. It sits outside the product system boundary, capturing potential benefits from reuse, recycling, or energy recovery that occur after the product leaves the defined system.

The logic is this: when steel is recycled, producing new steel from scrap requires less energy than producing virgin steel from iron ore. This avoided impact is credited in Module D. When wood is incinerated with energy recovery, the energy generated substitutes for other energy sources. This substitution benefit appears in Module D.

What goes into Module D:

• Material recycling benefits from displacing virgin material production
• Energy recovery benefits from substituting for fossil fuel energy
• Avoided burdens from reuse in subsequent life cycles
• Exported materials’ potential benefits

EN 15804+A2 specifies exactly how to calculate Module D:

• Net flows leaving the system (recycled materials, recovered energy)
• Substitution potential based on what those materials or energy replace
• Credits based on current average technology, not best-case scenarios
• Elementary flows related to material inherent properties (biogenic carbon content, carbonation potential)

Why Module D is controversial: It credits benefits that happen in the future, outside the product’s life cycle, and depend on market conditions. If recycling markets collapse, the credited benefits don’t materialise. If energy recovery efficiency improves, actual benefits might exceed what was credited. If worse, they might fall short.

Module D also creates comparison confusion. One product might show high Module C impacts but large Module D benefits. Another shows low Module C and small Module D benefits. Which is better? The answer depends whether you believe the recycling scenarios will happen as described.

EN 15804 is explicit: “EPD that are not in a building context are not tools to compare construction products.” Module D especially requires building context for meaningful comparison. At building level, you can evaluate whether recycling infrastructure exists, whether markets for secondary materials are stable, and whether credited benefits are realistic.

Some users include Module D in total impact calculations. Others exclude it, arguing that future benefits are too uncertain. There’s no universal rule. The key is consistency. If comparing products, treat Module D the same way for all options.

What dominates Module D? Materials with established recycling systems (steel, aluminium, glass) show large negative numbers (benefits) in Module D. Materials with energy recovery (wood, some plastics) show energy substitution benefits. Materials with limited recycling or recovery show small or zero Module D.

Biogenic carbon creates special Module D complexity for timber and bio-based products. Carbon stored in wood shows up in Module D when the wood product displaces fossil fuel use at end of life or when the biogenic carbon content is accounted for.

Comparing Modules Across Products#

The modular structure enables comparison, but you must compare correctly.

Same modules only: Compare A1-A3 to A1-A3, not A1-A3 from one EPD to A1-A3 plus C plus D from another. If EPDs cover different modules, compare only the overlapping ones or request data for matching scope.

Check scenarios: Two products’ Module C might differ because one assumes 90% recycling and one assumes 50%, not because the products are genuinely different. Compare the scenarios before concluding anything about products.

Consider the building context: A product with higher A1-A3 but lower B6 might have lower total impacts in a building assessment than one with lower A1-A3 but higher B6. The modules let you see these tradeoffs.

Understand what’s optional: Not all EPDs report all modules. Some report only A1-A3 plus C and D. Others include A4-A5. Construction products following EN 15804+A2 must report A1-A3, C, and D as minimum. Comparing EPDs with different module coverage requires care.

The Modular Structure in Practice#

When you read an EPD, the modular structure appears as columns in the impact results tables. Each impact category (climate change, acidification, etc.) is reported as a row, with columns for each module showing that module’s contribution.

This layout lets you see instantly where impacts occur. If 95% of climate change impact appears in A1-A3, you know production dominates. If B6 shows a large negative number (benefit), you know operational performance matters. If Module D shows large credits, recycling is significant.

For products where you have design choices, the modules guide where to focus improvement efforts. High A1-A3 suggests looking at material selection or manufacturing efficiency. High B4 suggests durability improvements. High C suggests design for disassembly or recyclability.

From Modules to Impact Categories#

The modules tell you when and where impacts occur. The impact categories tell you what types of impacts happen. Together, they create a two-dimensional view: life cycle stage (modules) crossed with environmental impact type (categories).

Understanding modules is half the picture. Understanding what the numbers in each module actually measure requires understanding the impact categories, which is where the next article in this guide takes you.

The modular structure transforms EPDs from single-number simplicity into detailed transparency. That complexity serves purpose. It enables building-level assessment, supports stage-by-stage comparison, reveals tradeoffs between life cycle stages, and helps identify where improvements matter most. Learning to read the modules turns EPD tables from confusing grids into information that guides better decisions