Category 1 — purchased goods and services — is where most construction and manufacturing companies have their largest Scope 3 footprint. This guide explains how to calculate it from a Bill of Materials using activity-based factors, and where FastLCA's free calculator fits in.
Under the GHG Protocol Corporate Value Chain (Scope 3) Standard, Category 1 covers all upstream emissions from goods and services you purchase — everything your suppliers emit to produce the materials that arrive at your door.
For a construction company, this typically means: concrete, steel, timber, insulation, glass, and every other material in your bill of materials. For a manufacturer, it means your raw material and component inputs.
Category 1 is almost always the largest Scope 3 category for material-intensive businesses — often 60–90% of total Scope 3 emissions. Yet it's frequently underreported because calculating it requires either spend-based estimates (inaccurate) or activity-based calculations (more work, but far more accurate).
💡 The key insight: You can optimise Scope 1 and 2 (energy, fleet, buildings) for years and still have 80%+ of your total carbon footprint sitting untouched in the materials you purchase. Cat 1 is where the real leverage is.
Multiply spend (£) by an emissions intensity factor (kg CO₂e/£). Works when you have no other data. Accuracy is typically ±300–500% because prices vary enormously and tell you nothing about the actual carbon content of what you bought. The GHG Protocol accepts this as a starting point but recommends moving to activity-based as soon as possible.
Multiply physical quantities (kg, tonnes, m³) by an emission factor (kg CO₂e per unit). This is what FastLCA does. Accuracy is typically ±10–50% depending on whether you use generic industry averages (DESNZ 2025) or product-specific EPD values.
⚠ DESNZ material factors vs EPD values: DESNZ 2025 material factors are UK industry averages — accurate to ±50% for specific products. For formal Scope 3 disclosure, replace average factors with supplier EPD A1–A3 GWP-total values where available. EPD values are product-specific and typically accurate to ±10–20%.
The UK Government's DESNZ 2025 conversion factors provide activity-based Category 1 factors for common construction materials, expressed as kg CO₂e per tonne of primary production:
| Material | kg CO₂e / tonne | Source |
|---|---|---|
| Aggregates | 7.79 | DESNZ 2025 Material use |
| Asphalt | 39.21 | DESNZ 2025 Material use |
| Bricks | 241.79 | DESNZ 2025 Material use |
| Concrete | 118.79 | DESNZ 2025 Material use |
| Insulation | 1,861.79 | DESNZ 2025 Material use |
| Metals (avg) | 3,824.09 | DESNZ 2025 Material use |
| Plasterboard | 120.05 | DESNZ 2025 Material use |
| Wood / timber | 269.50 | DESNZ 2025 Material use |
| Glass | 1,402.77 | DESNZ 2025 Material use |
| Plastics (avg) | 3,172.50 | DESNZ 2025 Material use |
Note that metals and insulation have very high factors relative to their weight — even small quantities can dominate your Category 1 total. Steel in particular deserves attention: 1 tonne of structural steel produces roughly 3,824 kg CO₂e upstream, compared to 119 kg for concrete. On a typical construction project, steel often accounts for 40–60% of total Category 1 emissions despite being a fraction of the total mass.
ℹ Unit conversions: DESNZ factors are per tonne. If your BoM has quantities in kg, divide by 1,000. If in m³, multiply by the material's density (kg/m³) then divide by 1,000. FastLCA handles these conversions automatically — including m³ to tonnes via built-in densities for each material.
DESNZ factors are industry averages — they're a reasonable starting point but can be significantly off for specific products. For example, electric arc furnace (EAF) steel has roughly 70% lower emissions than blast furnace steel, but both are averaged together in the DESNZ metals factor.
Use supplier EPD values when:
EPD A1–A3 GWP-total values are available from EPD Norway, IBU, Environdec, and EPDHub.
FastLCA's Scope 3 calculator covers Cat 1–6 using DESNZ 2025 factors. Enter quantities in kg, tonnes, or m³ — unit conversion is automatic. Override any factor with your own EPD data.
Open Scope 3 calculator →The GHG Protocol requires you to include all Category 1 emissions that are material — typically defined as anything contributing more than 1% of total Scope 3. In practice, concrete, steel, timber and insulation cover 80–90% of Category 1 for most construction businesses. Start with these and add other materials as data becomes available.
Embodied carbon (A1–A3 in EN 15804 terms) refers to the production-stage GWP of construction materials — which is exactly what Category 1 captures. They measure the same thing from different reporting frameworks: Scope 3 is a corporate emissions accounting framework, while embodied carbon / LCA is a product-level assessment framework. FastLCA covers both.
FastLCA provides indicative estimates suitable for early-stage screening and internal tracking. For formal regulatory disclosure, results should be reviewed by a qualified sustainability professional and ideally supported by supplier EPD data rather than generic DESNZ averages.
DESNZ publishes updated conversion factors annually, usually in June. The concrete/cement factor changed significantly between 2021 and 2022 (up ~119%) due to a methodology revision. FastLCA uses the 2025 edition — always check the factor year when comparing results year-on-year.