Insulation product LCA: U-value, lambda, RC and the functional unit

The most common mistake in insulation LCA is comparing materials by mass. Glass wool, stone wool, EPS, XPS, PIR/PUR, wood fibre — these six main categories have different densities and different thermal performance; "1 kg" comparison is unfair. EN 16783 PCR therefore ties the functional unit to thermal performance.

λ, RC, U — three critical parameters

• λ (lambda) — thermal conductivity, W/m·K. How well it insulates; low λ = good. Glass wool ~0.034, EPS ~0.036, PIR ~0.024
• RC (thermal resistance), m²K/W. RC = thickness (m) ÷ λ. 100 mm glass wool = 0.1 / 0.034 = 2.94 m²K/W
• U (thermal transmittance), W/m²K. U = 1 / total RC. Low U = low loss. Passive house target U ≤ 0.15 W/m²K

EN 16783 functional unit choice

EN 16783 offers two options: (a) "1 m² of product providing 1 m²K/W of RC" (RC-based), or (b) declared unit as "1 m² of product at a specified thickness". The RC-based choice is fair — it automatically balances products with different λ values. Comparing PIR (λ=0.024) with glass wool (λ=0.034): for the same RC, PIR needs less mass, so A1-A3 emissions are lower. Glass and stone wool lack low-λ advantage and carry mass disadvantage; they recover via ECO-Platform CDM scoring (fire safety, recyclability).

B6 — use-phase energy savings

The most contested module in insulation LCA is B6. Insulation's very purpose is to save energy; you may want B6 to report this as a positive environmental benefit. EN 16783 makes this optional but conditional: specific climate zone (European Cold/Temperate/Warm), building type, energy-mix assumptions must all be documented. A product's real B6 benefit over 50-year service life can be -10 to -50× the embodied emissions; the A1-A3 burden is repaid hundreds of times. A powerful marketing message — but it must be documented.

A5 — installation waste

A5 waste rates by insulation type: board products (glass wool, stone wool, EPS, XPS) 3-8% (cutting waste, geometry mismatch); spray foams (PIR/PUR) 1-2% (overspray); ETICS systems 5-10% (corner, joint, cutting). EN 16783 mandates a 3% minimum; verifiers reject anything below it. If the installer has on-site waste measurement, use it; otherwise back-calculate from annual supply-vs-sales delta.

C and D — end-of-life category split

End-of-life varies dramatically by category. Glass and stone wool can be cullet-recycled — actual recycle rate 20-40%, with frequent down-cycling; modest Module D credit. EPS sees energy recovery (incineration) 50-70%; absent renewable energy the Module D carbon credit is small, but in a co-gen plant it counts as fossil-fuel substitution. PIR/PUR and wood fibre lean to energy recovery; PIR has the paradoxical advantage of long-term landfill carbon storage (CO₂ stays out of the atmosphere).