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.

AI-Powered SAP Assessment

SAPPER uses advanced AI to automate SAP (Standard Assessment Procedure) calculations for UK Building Regulations Part L compliance. Extract data from drawings, calculate thermal performance, generate professional reports.

AI Capabilities

AI Drawing Analysis

Upload architectural PDFs and our AI automatically extracts floor areas, perimeters, storey heights, window dimensions by orientation, and construction details. Multi-pass extraction with quality verification ensures 85-95% accuracy.

PDF extractiondrawing analysisdimension detectionfloor plan analysis

Automated SAP Calculations

AI-powered calculation engine computes U-values, heat loss parameters, thermal bridging Y-values, solar gains, space heating demand, and SAP rating. Follows SAP 10.2 methodology with full audit trails showing all calculation steps.

SAP calculationU-valueheat lossthermal performanceenergy rating

Thermal Bridge Intelligence

Automatically identifies and calculates 15+ junction types using BRE accredited psi-values. Supports RCD (Recognised Construction Details) optimization for brick/block constructions. Includes condensation risk assessment per BR 497.

thermal bridgingpsi-valuesRCDcondensation riskjunction analysis

AI Report Writing

Generates professional narrative sections for compliance reports including executive summary, thermal performance analysis, thermal bridging assessment, compliance statements, and improvement recommendations. Context-aware and regulation-compliant.

AI writingcompliance reportsSAP narrativetechnical writing

Part L Compliance Checking

Validates against Part L 2013 and Part L 2021 standards using Average U-value method (extensions < 50m²) or Whole House comparison method (extensions > 50m² or conservatories). Instant pass/fail feedback with improvement suggestions.

Part L complianceBuilding Regulationscompliance checkingenergy standards

Smart Optimization

AI identifies optimization opportunities including RCD psi-value upgrades, condensation risk mitigation, thermal performance improvements, and cost-effective compliance strategies. Prioritizes recommendations by impact and feasibility.

optimizationenergy efficiencycost savingsdesign improvements

Who Uses SAPPER?

SAP Assessors

Speed up data entry from drawings, verify calculations, generate draft reports, optimize thermal bridging strategies, streamline assessment workflow

Architects & Designers

Check Part L compliance during design phase, optimize U-values before submitting to Building Control, explore construction options, generate pre-submission reports

Developers & Builders

Validate designs before construction, compare construction methods, estimate compliance costs, prepare for Building Control inspections

Homeowners

Understand Part L requirements for extensions, validate builder proposals, get independent assessments, learn about energy performance

AI Technology Stack

Vision AI for Drawing Analysis

Analyzes architectural drawings using computer vision to detect scales, dimensions, orientations, and building elements. Multi-pass extraction with classification, measurement, and verification stages.

LLM for Calculations & Reasoning

Large Language Models perform SAP 10.2 calculations following UK standards. Handles complex scenarios like Room in Roof, party walls, thermal bridging optimization, and regulation compliance checking.

Natural Language Report Generation

AI writes professional compliance narratives explaining thermal performance, thermal bridging impact, compliance status, and recommendations. Tailored to project specifics with technical accuracy.

Data Security & Privacy

✅ All project data is stored securely in your private account

✅ PDF drawings are processed temporarily and not retained by AI models

✅ GDPR compliant data handling

✅ No third-party sharing of project information

✅ SSL encryption for all data transmission

Free to use • No credit card required • Professional results in minutes