What is a WLCA?
A Whole-Life Carbon Assessment (WLCA) quantifies the total greenhouse gas emissions associated with a building across its entire lifecycle - from raw material extraction through construction, operation, maintenance, and end of life. It follows the EN 15978 standard and the RICS Professional Statement on Whole Life Carbon Assessment.
The WLCA combines embodied carbon (Modules A, B4–B5, C) with operational carbon (Module B6 for energy, B7 for water) to give a complete picture of the building's climate impact.
Step 1: Define scope and building model
Start with a clear scope definition. Which lifecycle modules are you assessing? What is the reference study period (typically 60 years for UK buildings)? What is the functional equivalent - the building's size, function, and performance requirements?
You'll need a building information model or bill of quantities that identifies all significant materials and their quantities. At RIBA Stage 2, this can be based on elemental cost plan data. By Stage 4, it should reflect detailed design quantities.
Step 2: Assign carbon data
For each material, assign embodied carbon data. The hierarchy of data quality is:
1. Product-specific EPDs - most accurate 2. Industry-average EPDs - good where product hasn't been specified 3. Generic database values (ICE, KBOB) - acceptable as defaults
For operational energy, use Part L compliance modelling or dynamic energy simulation results. Apply carbon emission factors from the government's SAP methodology or the grid decarbonisation projections.
Step 3: Calculate and benchmark
Sum the emissions across all modules and lifecycle stages. Express results as kgCO₂e per m² of gross internal area (GIA) to enable benchmarking.
Compare against established benchmarks: LETI targets (500 kgCO₂e/m² for residential upfront carbon), RIBA 2030 Challenge targets, and emerging Part Z limits. Identify which materials and building elements contribute the most - typically structure and substructure dominate, followed by external envelope.
Step 4: Identify reduction opportunities
Use the assessment results to inform design decisions. Where are the carbon hotspots? Can you substitute high-carbon materials for lower-carbon alternatives without compromising performance? Can you reduce quantities through structural optimisation?
Our Carbon Calculator helps with this step - input your specification, see the total impact, and discover alternatives that could reduce your project's embodied carbon by 20–40%.
Key Takeaways
- WLCA covers both embodied and operational carbon across the full lifecycle
- Follow EN 15978 and RICS Professional Statement methodology
- Product-specific EPDs give the most accurate data
- Benchmark against LETI (500 kgCO₂e/m²) and RIBA 2030 targets
- Structure and substructure typically dominate embodied carbon - focus there first
Ready to calculate your project's carbon impact?
Use our Carbon Calculator to specify materials and discover lower-carbon alternatives.
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