A U-value calculation quantifies the rate of heat loss through a construction element (wall, floor, roof, window, door) per square metre per degree of temperature difference. Every new-build and most refurbishment projects need U-values as the fundamental fabric input to SAP, SBEM and Building Regulations Part L compliance.
We calculate U-values to BRE Report BR 443 "Conventions for U-value calculations" using the combined method for framed constructions (BS EN ISO 6946). For window and door U-values we use manufacturer-declared BFRC / CE-marking values or calculate to BS EN ISO 10077 as appropriate.
A clear build-up specification — layer names, thicknesses, thermal conductivity (λ) values, and any airspace or bridging details. A sketch or drawing extract is usually enough. If you only have material names, we'll look up conductivity values from published product data or CIBSE Guide A defaults.
External walls (masonry cavity, timber frame, SIPs, ICF, hempcrete, straw bale, cob, retrofit internal or external insulation), ground floors (slab-on-grade, suspended timber, beam & block, retrofit), roofs (pitched, flat, warm and cold deck constructions), windows and doors.
U-value calculations are often paired with a Condensation Risk Analysis (CRA) to check for interstitial condensation within the build-up. We offer CRA as a £30 add-on to any U-value calculation — essential for non-standard or breathable constructions, retrofit projects and traditional buildings.
From £50 per calculation. Bulk pricing available for full-project U-value packs (typically 6–10 build-ups covering walls, floors, roofs, glazing). Delivered 2–3 working days from receipt of specifications; same-day service on request.
Current Part L 2021 (Volume 1) notional targets are 0.18 W/m²K for walls, 0.13 W/m²K for floors, 0.11 W/m²K for pitched roofs (insulation at ceiling) and 0.16 W/m²K for flat roofs. New windows should achieve 1.4 W/m²K or better. These are notional targets — the actual required U-values are set by the overall SAP or SBEM model, so poor-performing elements can be offset by better-than-notional elements elsewhere.
Yes. Hempcrete, straw bale, cob, SIPs, ICF, timber frame with I-joists, MMC panellised systems and retrofit internal or external wall insulation are all standard work for us. We use BR 443 combined-method for framed elements and product-specific declared conductivities where available.
Each calculation is delivered as a PDF report showing the full layer-by-layer build-up, conductivity sources, calculation method, corrected U-value with air-layer and mechanical-fastener corrections applied, and a clear statement of the Part L target it is designed to meet. Suitable for direct submission to Building Control.
A U-value quantifies heat loss through one square metre of one construction element. A heat-loss calculation (for boiler / heat-pump sizing) uses your U-values plus room-by-room geometry, ventilation and design temperatures to give the total heat demand of the building in watts. Both use the same fabric numbers but answer different questions. See our independent heat load calculations page for the room-by-room service.
Call 01392 980077 or get a quote online.