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Let’s break down how the avoided emissions values of ~1.5–2.5 tCO₂eq/m³ are obtained when replacing reinforced concrete or steel with timber, using the EN 16449 and EN 15978 standards as the foundation.
🧩 Step-by-Step Breakdown of the Calculation
🧩 Step-by-Step Breakdown of the Calculation
1. Determine the Functional Unit
1. Determine the Functional Unit
Typically 1 cubic meter (m³) of material is used as the unit of comparison.
This ensures a consistent basis for comparing timber, concrete, and steel.
2. Calculate Embodied Carbon of Each Material (EN 15978)
2. Calculate Embodied Carbon of Each Material (EN 15978)
EN 15978 defines how to assess embodied carbon across the life cycle stages:
🔧 Example Embodied Carbon Values (A1–A3 only):
Reinforced Concrete: ~2.5–3.0 tCO₂eq/m³
Structural Steel: ~10–12 tCO₂eq/m³
Timber (e.g., glulam): ~0.3–0.5 tCO₂eq/m³
These values come from Environmental Product Declarations (EPDs) and LCA databases like Ökobaudat, ecoinvent, or OneClick LCA.
3. Account for Biogenic Carbon Storage (EN 16449)
3. Account for Biogenic Carbon Storage (EN 16449)
EN 16449 defines how to calculate biogenic carbon stored in wood:
Carbon content of dry wood ≈ 50% of mass
Conversion factor: 1 kg of carbon = 3.667 kg of CO₂
For 1 m³ of wood (~500 kg dry mass), stored carbon ≈ 250 kg → ~0.9 tCO₂eq stored
This is temporarily removed from the atmosphere and stored in the building for decades.
4. Calculate Avoided Emissions
4. Calculate Avoided Emissions
Avoided emissions =
(Embodied carbon of replaced material) − (Embodied carbon of timber) − (Biogenic carbon stored)
🧮 Example:
Replacing 1 m³ of reinforced concrete:
Concrete: 2.7 tCO₂eq
Timber: 0.4 tCO₂eq
Biogenic storage: −0.9 tCO₂eq
→ Avoided emissions = 2.7 − 0.4 − 0.9 = 1.4 tCO₂eq
Replacing steel:
Steel: 11 tCO₂eq
Timber: 0.4 tCO₂eq
Biogenic storage: −0.9 tCO₂eq
→ Avoided emissions = 11 − 0.4 − 0.9 = 9.7 tCO₂eq
5. Adjust for System Boundaries and End-of-Life
5. Adjust for System Boundaries and End-of-Life
If the wood is landfilled or incinerated, the stored carbon may be released.
If it’s reused or recycled, the storage may be extended or credited in Module D.
📘 Summary Table
📘 Summary Table
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