Building Fabric Check

U-Value Calculator

A fast spec-stage calculator for retrofit assessors, architects, contractors, and building-physics teams comparing realistic wall, floor, and roof build-ups.

Built for real optioning conversations: sketch the build-up, test where bridges matter, then save the assemblies worth taking into design review or client sign-off.

Use: early-stage envelope optioning Checks: walls, roofs, ceilings, floors Method: ISO 6946 style assembly logic

Calculated Assembly Performance Wall build-up Lower values mean less heat loss through the element. Use this as a fast design-stage check before detailed modelling or certification.

Typical target ≤ 0.18 W/m²K

-- W/m²K

Total R: -- m²K/W Thickness: -- mm

Element type

applies ISO 6946 default surface values

Material layers

outside to inside, as proposed

Advanced: adjust surface resistances

These are set automatically from the selected element, but you can override them if your calculation note calls for different ISO 6946 assumptions.

Rsi (internal)

Rse (external)

Saved options

keep shortlisted assemblies together

U = 1 / R_total, where R_total = R_si + Σ(d / λ) + R_se. Multi-material layers such as timber studs plus insulation use the ISO 6946 combined method, averaging upper and lower resistance limits. This is intended for early design and retrofit decision-making, not as a substitute for certified project calculations.