AI-assisted · Human-verified · Fully auditable
Upload a construction drawing. AI reads the build-up, a deterministic BS EN ISO 6946 engine does the maths, and you get a Building Control ready report — with every step shown.
No signup required. First analysis is free.
Calculated U-value
0.17W/m²K
Part L new-build target 0.18
Cavity wall — AI extracted
BS EN ISO 6946
~10s
average AI analysis
BR 443
conventions applied
ISO 6946
deterministic engine
PDF + XLSX
Building Control reports
How it works
AI does the reading, not the maths. Layer extraction is AI-assisted; the calculation itself is a deterministic ISO 6946 engine you can audit.
01
Drag in a construction detail, section drawing, or specification. PDF, PNG or JPEG — straight from your CAD export.
02
Every layer, thickness and λ-value is identified and flagged as AI-suggested until you confirm it. Nothing is hidden.
03
PDF and Excel reports with the full methodology, sources and Part L check — ready for Building Control submission.
Coverage
All common UK construction types, with thermal bridging from studs and fixings handled automatically.
Trust through transparency
Black-box results don't survive Building Control. Ours aren't black boxes: the AI only suggests — the numbers come from a deterministic engine, and the report shows how.
calculation-steps.txt
# BS EN ISO 6946 — simple addition of resistances
Rse (external surface) 0.0400
Brick outer leaf 102.5/770 0.1331
Cavity (unventilated, Table 2) 0.1800
PIR board 100/22 4.5455
Aircrete block 100/110 0.9091
Plaster 13/400 0.0325
Rsi (internal surface) 0.1300
ΣR total 5.9702 m²K/W
U = 1/ΣR 0.17 W/m²K ✓
# Part L 2021 new-build wall target: 0.18 — PASS
Deliverables
The exact methodology UK Building Regulations require. Correct surface resistances, bridged layers via the combined method, and official design values.
Spreadsheets with visible, verifiable formulas — Building Control can check every step. Perfect for audit trails.
Professional reports with methodology, assumptions, material sources and the Part L compliance check included.
Instant comparison against new-build, extension and renovation targets, for England and Scotland (Section 6).
Quick reference
| Element | New build | Extension | Renovation |
|---|---|---|---|
| External wall | 0.18 | 0.28 | 0.30 |
| Roof — pitched, insulation at ceiling | 0.11 | 0.16 | 0.16 |
| Roof — flat or pitched at rafter | 0.11 | 0.18 | 0.18 |
| Ground floor | 0.13 | 0.18 | 0.25 |
Values in W/m²K. Consult Approved Document Part L for full requirements and exceptions.
FAQ
A U-value (thermal transmittance) measures how effective a building element is as an insulator. It's expressed in watts per square metre kelvin (W/m²K) and represents the rate of heat transfer through a structure. Lower U-values indicate better insulation. Under UK Building Regulations Part L, all thermal elements must meet minimum U-value requirements.
Upload a construction detail, section drawing, or specification (PDF, PNG, or JPEG). Our AI analyses the image to identify all layers and materials, determines thermal conductivity values from BR 443 and manufacturer data, handles thermal bridging from timber studs or metal fixings, and calculates the U-value following BS EN ISO 6946 methodology.
Yes, all calculations follow BR 443 conventions and BS EN ISO 6946 methodology as required for UK Building Regulations. The calculator uses official design thermal conductivity values and applies correct surface resistances. Generated reports include full methodology for Building Control submission.
The AI can analyse all common UK construction types including cavity walls, solid walls, timber frame, SIPS, pitched roofs (at ceiling or rafter level), flat roofs (warm deck and cold deck), ground floors (solid and suspended), and more. Thermal bridging from repeating elements like studs is automatically calculated.
For new build dwellings: walls 0.18 W/m²K, floors 0.13 W/m²K, roofs 0.11 W/m²K. For extensions: walls 0.28, floors 0.18, roofs 0.16-0.18 W/m²K. For renovations: walls 0.30, floors 0.25, roofs 0.16-0.18 W/m²K. The calculator automatically checks compliance against these targets.
Yes, you can download professional PDF and Excel reports that are ready for Building Control submission. Reports include the full calculation methodology, material properties with sources, surface resistances, thermal bridging adjustments, Part L compliance status, and all assumptions made.
U-Value.com uses advanced AI technology to analyse your construction drawings and calculate thermal transmittance (U-values) automatically. Simply upload a section detail, specification, or construction drawing, and our AI will identify all the layers, determine appropriate thermal conductivity values, and calculate the U-value following BR 443 and BS EN ISO 6946 standards.
Our AI understands common UK construction materials and methods, including thermal bridging from timber studs, metal fixings, and other repeating elements. The system references BR 443 design values and manufacturer declared values to provide accurate results.
A U-value (thermal transmittance) measures how effective a building element is as an insulator. It's expressed in watts per square metre kelvin (W/m²K) and represents the rate of heat transfer through a structure. Lower U-values indicate better insulation.
Generate professional PDF and Excel reports that include full calculation methodology, material properties, surface resistances, and Part L compliance checking. These reports are formatted for Building Control submission and include all the information required to demonstrate compliance with UK Building Regulations.