Eco Build Directory — Eco building materials | ecobuilddirectory.com
A numbered procedure from performance target to written specification, with the failure modes that most often derail a low-carbon choice.
Step 1 — set the performance target. Choose a U-value for each element of the extension; 0.20 W/(m²K), for instance, implies a total R-value of 5 m²K/W across the build-up. Allow one to two days, and write the target down — every later decision refers back to it.
Step 2 — size the layer. Subtract the R-value of the other layers, then multiply the remainder by each candidate's declared lambda. For an insulation R of 4.5 that means 81–90 mm of aerogel, 140–171 mm of EPS, 144–180 mm of mineral wool or 171–225 mm of wood fibre. Two to three days suffices for the arithmetic.
Step 3 — check embodied carbon. Insulation saves carbon in use, but the structure spends it upfront: a cubic metre of standard concrete carries 150–360 kg of CO₂ from its 300–400 kg of cement alone. Ask suppliers for cement content per cubic metre and compute the range yourself.
On narrow screens, swipe or scroll the plate sideways.
Step 4 — verify the paperwork. Request the Declaration of Performance and any certificates; check Cradle to Cradle level and its 2-year validity, the USDA 72% biobased minimum where claimed, and formaldehyde class for boards. Allow one to two weeks for documents to arrive — a missing declaration is failure mode one.
Step 5 — write the specification. Record product, thickness, declared lambda, certificate numbers and junction detailing. From target to signed-off specification, the whole procedure typically takes two to four weeks, most of it waiting on step four.
The named failure modes: thermal bridging where the layer is interrupted, air leakage where membranes are unsealed, interstitial condensation where vapour control is an afterthought, settlement of loose-fill in tall cavities, expired certificates, and unapproved substitutions on site. Each maps to a step above, which is where it should be caught.
Further reading