WLCA divides a building’s life into modules A1 through D, each capturing specific carbon emissions. This structure from EN 15804:2011+A2:2019 ensures consistent reporting across all construction projects. Think of these modules as the chapters in your building’s carbon story, from cradle to grave and beyond.
Quick Module Overview
The modules follow your building’s journey through time:
Module A covers getting it built (product and construction stage)
Module B tracks keeping it running (use stage)
Module C accounts for taking it down (end of life stage)
Module D captures what happens next (benefits and loads beyond the system boundary)
Module A: Product and Construction Stage
A1-A3: Product Stage
These three modules capture the carbon embodied in materials before they reach your site. Manufacturers typically report A1-A3 combined in their EPDs because they control all three stages.
A1: Raw Material Extraction is where it all begins. Quarrying aggregates for concrete, mining iron ore for steel, harvesting timber from forests, extracting petroleum for plastics. Every material starts with extraction, and every extraction has a carbon cost.
A2: Transport to Manufacturing moves these raw materials to factories. Ships carrying iron ore across oceans, trains hauling aggregates to cement plants, trucks delivering timber to sawmills. The distances matter, and the transport mode matters more.
A3: Manufacturing transforms raw materials into construction products. Cement kilns firing at 1,450°C, steel furnaces melting and rolling, timber being sawn and treated, insulation materials being formed and packaged. This is often where the largest carbon emissions occur, especially for energy-intensive materials like steel and cement.
A4: Transport to Site
Every delivery truck arriving at your site contributes to A4. The RICS PS 2024 (Section 5.1.3) provides default distances when you don’t have specific data:
Concrete typically travels 50km by road from batching plant to site. Steel comes 230km nationally or 430km from European suppliers. Timber journeys 640km from European forests. But if you know your supply chain, real data always beats defaults.
A5: Construction and Installation
A5 captures everything that happens on site to build your asset. This breaks down into several components:
Pre-construction demolition (A5.1) clears existing structures, reported separately to maintain transparency about what was there before.
Groundworks and landscaping (A5.2) prepare the site for construction.
Installation emissions (A5.3) include energy for cranes and tools, power for site cabins, heating for winter working, and waste from cutting and fitting. Expect 5-15% waste by mass during construction. That’s offcuts, damaged materials, and over-ordering.
Worker transport (A5.4) can be included but rarely is due to data complexity.
Additional materials (A5.5) covers things made on site, like mortar mixed with water or materials cut to size.
Module B: Use Stage
The operational life of your building, typically assessed over 60 years according to RICS PS 2024 Section 4.2. This is where most emissions occur for traditional buildings, though this balance is shifting as buildings become more efficient.
B1: Use
Direct emissions from the building itself during operation. The big one here is refrigerant leakage from cooling systems, calculated as charge size times annual leakage rate times refrigerant GWP. A small office might leak 5% of its 10kg R-410A charge annually, creating significant emissions over 60 years. Green roofs might emit from fertilisers. But this doesn’t include what occupants do, just what the building does.
B2: Maintenance
Routine upkeep that preserves function without replacing components. Annual cleaning, repainting every 5-10 years, facade cleaning, gutter clearing. These activities seem minor individually but accumulate over six decades. Each tin of paint, each cleaning chemical has embodied carbon.
B3: Repair
Restoring function after unexpected damage. Fixing storm-damaged roofs, repairing settlement cracks, replacing broken window mechanisms. Based on component failure rates and historical data. Unlike planned maintenance, repairs respond to failures.
B4: Replacement
Complete component renewal when things reach end of service life. Windows typically last 30 years, so you’ll replace them once in a 60-year assessment. Boilers survive 15 years, meaning three replacements. Flat roofs need replacing every 20 years. Lifts last about 25 years.
Service lives come from ISO 15686-1:2011 or manufacturer warranties. This module often contributes 10-20% of total embodied carbon, yet frequently gets forgotten in assessments.
B5: Refurbishment
Major renovation that changes building function or performance. Converting offices to apartments, adding new floors, comprehensive energy retrofits. Assessed as a separate WLCA then integrated into the original building’s assessment (RICS PS 2024, Section 5.2.5).
B6: Operational Energy Use
Energy consumed by building services over its lifetime. Heating and cooling to maintain comfort, lighting for visibility, ventilation for air quality, small power for equipment, lifts and escalators for circulation.
Calculated using SBEM, DSM, or PHPP models. Crucially, you must apply Treasury Green Book grid decarbonisation factors. The electricity your building uses in 2050 will be far less carbon intensive than today’s, assuming the grid continues to decarbonise.
B7: Operational Water Use
Emissions from water supply and treatment. Every cubic metre supplied has embedded energy from treatment and pumping. Every cubic metre discharged requires wastewater treatment. Based on building type and occupancy levels, often using BREEAM benchmarks.
B8: Other Operational Emissions
User emissions beyond the base building, usually excluded. Occupant commuting, plug-in equipment, process energy for industrial buildings. Difficult to predict and often outside the design team’s influence.
Module C: End of Life Stage
What happens when your building reaches its end, typically after 60 years.
C1: Deconstruction/Demolition
Energy for demolition equipment, temporary propping for safety, dust suppression systems, sorting materials on site. The RICS PS suggests 3.5-4.0 kgCO₂e/m² GIA as a default. Deconstruction (careful dismantling) uses less energy than demolition but takes longer.
C2: Transport
Moving waste and materials from site to their next destination. Waste to treatment facilities, recyclables to processing plants, reusable materials to storage. Use waste contractor data when available, otherwise regional averages. Every skip that leaves site contributes to C2.
C3: Waste Processing
Treatment preparing materials for disposal or recovery. Crushing concrete into recycled aggregate, shredding timber for biomass fuel, processing steel for remelting, sorting mixed waste. Each process has its own carbon intensity.
C4: Disposal
Final disposal for materials that can’t be recovered. Landfill creates methane emissions over decades. Incineration without energy recovery releases carbon immediately. UK default rates assume 10% landfill, 39% incineration, 51% recycling, but better rates are achievable with good waste management.
Module D: Beyond the System Boundary
Credits and burdens from circular economy benefits, always reported separately from A-C totals. This captures the benefit of designing for disassembly and specifying recyclable materials.
D1: Reuse
Avoided emissions when materials get directly reused. Those reclaimed steel beams going into another project avoid new steel production. Reused bricks avoid manufacturing emissions. But you need demonstrable reuse routes, not just wishful thinking.
D2: Recovery
Energy recovery from waste processing, mainly incineration. Timber waste generating electricity avoids grid emissions. The avoided emissions depend on what energy source is displaced, using current grid factors at time of recovery.
D3: Recycling
Avoided primary production from recycling materials. Steel recycling avoids iron ore extraction and processing. Crushed concrete provides aggregate, avoiding quarrying. Calculated using EN 15804 cut-off method for allocation.
Remember: Module D benefits cannot offset A-C emissions in reporting (RICS PS 2024, Section 6.2.1). They’re future potential, not current performance.
Reporting by Module
Results present each module separately to show where emissions occur:
Product stage (A1-A3) typically contributes 20-30% of whole life carbon Construction (A4-A5) adds 2-5% Use stage (B1-B7) dominates at 50-70% for most buildings End of life (C1-C4) contributes 1-3% Module D might show benefits of -5% to -15% but reports separately
Minimum Reporting Requirements
RICS PS 2024 mandates what you must include:
All projects must report A1-A5, B1-B7, and C1-C4. No exceptions for missing data; use defaults if needed.
Small projects under 1,000m² may exclude B6 predictive energy modelling, using benchmarks instead.
Module D always reports separately, never netted against the A-C total. This prevents greenwashing with uncertain future benefits.
Data Quality by Module
Different modules require different data precision:
A1-A3 needs EPDs where available, though generic data is acceptable for smaller items. Focus your EPD hunting on high-mass materials.
A4-A5 benefits from project-specific or contractor data. Those delivery records and site energy bills matter.
B1-B5 uses reference service lives and standardised scenarios. Consistency matters more than precision here.
B6-B7 requires calculated predictions using regulatory compliance models. This is where your energy modeller earns their fee.
C1-C4 relies on regional waste statistics and standard scenarios. Perfect prediction 60 years hence is impossible.
Module D demands conservative estimates with justified allocations. Better to understate than overstate benefits.
ISO 14044:2006 data quality requirements apply throughout, ensuring transparency about uncertainty.
Common Mistakes
Double counting happens when you include both replacement (B4) and refurbishment (B5) for the same component. Pick one based on your scenario.
Missing refrigerants in B1 seems minor but refrigerant leakage can contribute significantly to whole life carbon. Always check cooling systems.
Netting Module D against your total makes results look better but violates reporting requirements. Keep D separate.
Wrong service lives occur when assuming components last the full building life. Windows don’t last 60 years; they need replacing.
Forgetting B4 replacements leaves out 10-20% of embodied carbon. Every boiler, carpet, and roof replacement counts.
Understanding these modules transforms WLCA from overwhelming complexity to systematic assessment. Each module has its place, its purpose, and its data requirements. Master the structure, and the calculation follows.
For complete requirements, consult the RICS Professional Standard – Whole Life Carbon Assessment for the Built Environment (2024)
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