The smallest number in a list of EPDs is not automatically the best choice for a building. Product quantities, performance and system boundaries can change the decision. A useful comparison starts with the function required by the design, then examines the environmental information on a consistent basis.
Write the comparison question first
For example, compare alternative wall build-ups delivering the same specified performance across the same study period. Do not start with a list of unrelated products and ask software to rank them. Thickness, service life and technical suitability belong in the decision alongside the environmental result; the design team must confirm that the proposed options are genuinely acceptable substitutes.
Check units before multiplying
A result declared per kilogram is not directly comparable with a result per square metre. In an illustrative exercise, Product A at 2 kg CO2e/kg and 10 kg/m² gives 20 kg CO2e/m². Product B at 3 kg CO2e/kg and 5 kg/m² gives 15 kg CO2e/m². That arithmetic only makes a meaningful comparison if both options perform the same function and the other assessment conditions match. These are teaching figures, not product benchmarks.
Match the scope and method
Check PCR compatibility, module coverage, indicator definitions, validity and assumptions. A cradle-to-gate number should not be ranked against a cradle-to-grave total. Product Category Rules establish category-specific assessment and comparability requirements; a common document label alone is insufficient. EPD International explains the role of PCRs.
Choose representative data in One Click LCA
One Click LCA’s guidance emphasises eligible and representative data rather than selecting by verification status alone. Product identity, manufacturing technology, location and time all matter. A verified source for the wrong manufacturing route can be inappropriate; document the reason for any proxy. Read the official dataset-selection guidance.
Separate design changes from data improvements
Keep an unchanged baseline and a controlled option model. If quantities and datasets both change, record each change separately so the client can see what caused the difference. Replacing an early generic dataset with a supplier EPD improves specificity, but it is not necessarily evidence that the physical design became lower carbon. Label that distinction in the report.
Report the decision and its uncertainty
A useful options note states the common functional basis, quantities, included modules, study period and outstanding supplier assumptions. Show relevant impacts rather than reducing every environmental question to one carbon figure. Do not subtract a speculative end-of-life benefit from upfront carbon to make a favourable headline. The final specification should also consider cost, durability, fire performance and constructability.
Related guidance
- One Click LCA Building Assessments: From BIM Quantities to Reviewable Results
- One Click LCA EPD Data Collection: A Manufacturer’s Checklist
- EN 15978 life-cycle modules explained
Plan your LCA and EPD work
DOE Modellers supports building and product LCA using One Click LCA. Explore our LCA & EPD services or discuss the scope and evidence required for your project. HPD disclosure and independent verification are separate scopes to confirm.
Discuss your projectReviewed September 12, 2026. General technical guidance, not a certification or verification decision. Confirm current programme rules, standard editions and software entitlements for your project. DOE Modellers is not represented here as a programme operator or independent verifier.