Your streamlined solution for Part L Extension Compliance, ensuring your building projects meet regulatory standards with automated Average U-value calculations and clear compliance reports.

SAPPER is a free AI-powered SAP (Standard Assessment Procedure) compliance calculator for UK Building Regulations Part L. It automates data extraction from architectural PDF drawings, calculates thermal bridges, checks Part L compliance using Average U-value or Whole House methods, and generates professional compliance reports. Built by CoreLogic Ai Ltd.

What are the Part L 2021 U-value limits for extensions?

Part L 2021 (England, from June 2022) extension limiting U-values: External walls 0.18 W/m²K, Roofs 0.15 W/m²K, Floors 0.18 W/m²K, Windows 1.4 W/m²K, Doors 1.4 W/m²K, Rooflights 2.2 W/m²K. These are used as notional values in the Average U-value compliance calculation.

How does AI extract SAP data from drawings?

SAPPER uses a multi-pass AI extraction system: Pass 1 classifies drawing types (plans, elevations, sections) and detects scales. Pass 2 extracts dimensional data (floor areas, perimeters, storey heights) from annotations. Pass 3 analyses every elevation for windows, doors, rooflights with orientation detection. Results are validated with sanity checks and achieve 85-95% accuracy.

What are thermal bridge psi-values?

Psi-values (ψ-values) measure additional heat loss at building junctions in W/mK (Watts per metre Kelvin). Common UK junctions include E2 (lintels, accredited ψ=0.20), E3 (sills, ψ=0.04), E4 (jambs, ψ=0.04), E5 (ground floor, ψ=0.12), E10/E11 (eaves, ψ=0.04-0.06). RCD (Recognised Construction Details) values are 20-40% lower for brick/block masonry constructions.

What is the condensation risk f-factor?

The f-factor (fRsi) is the surface temperature factor used to assess condensation and mould growth risk at thermal bridges per BR 497. f ≥ 0.75 = low risk (acceptable), f 0.65-0.75 = medium risk (review needed), f < 0.65 = high risk (mould growth likely, design modification required). Calculated as fRsi = (Tsi - Te) / (Ti - Te).

Is SAPPER free to use?

Yes. SAPPER is completely free with no feature limitations, no credit card required, and no hidden costs. Part L calculator, AI extraction, thermal bridging, room in roof calculator, and PDF reports are all included at no charge.

SAP Calculation for Extensions | Part L 1B Compliance

What SAPPER does

SAPPER is an AI-powered platform that automates SAP (Standard Assessment Procedure) compliance calculations for UK dwelling extensions and new builds. It reads architectural drawings — including PDF floor plans, DXF CAD files, and IFC BIM models exported from Revit or ArchiCAD — and extracts the dimensions, U-values, and construction details needed to demonstrate compliance with Part L of the Building Regulations 2013 and 2021. Users can run an Average U-value check, a Whole House method assessment, calculate thermal bridge psi-values, evaluate condensation risk using BR 497, model Room-in-Roof storey heights with SAP 10.2 methodology, and generate fully branded compliance reports in minutes rather than hours.

Who it's for

SAPPER is built for SAP assessors, energy consultants, architectural technicians, architects, building control officers, retrofit coordinators, and small builders who need fast, defensible Part L compliance evidence for residential extensions, loft conversions, and new dwellings. It saves an average of 3.5 hours per project compared to manual measurement and calculation.

Who builds it

SAPPER is developed by CoreLogic AI Ltd (Company No: 16919694), a UK technology company specialising in regulatory AI tools for the built environment. It forms part of the wider UKRAES ecosystem of building regulation tools. Our team combines chartered surveyors, SAP assessors, and AI engineers to deliver accurate, transparent, and continuously improving compliance software.

About SAPPER

What SAPPER does

Who it's for

Who builds it

Part L Compliance

AI Extraction

Built for Professionals