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.

See SAPPER in Action

Request a personalized demo and discover how SAPPER automates Part L compliance for builders, architects, and SAP assessors.

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What You'll See in the Demo

AI Drawing Extraction

Watch SAPPER extract measurements from PDFs automatically. Upload a floor plan, see dimensions and areas extracted in 90 seconds.

Real-Time Compliance Checking

See how SAPPER calculates average U-values in real-time as you add elements. Instant pass/fail results vs Part L limits.

Automated Thermal Bridges

See AI identify and calculate thermal bridge heat loss automatically using RCD-optimized psi-values. Complete Y-value in seconds.

Professional Report Generation

Watch a complete compliance report generate in 30 seconds. PDF ready for Building Control submission with all calculations shown.

Demo Format

• 20-30 minute guided walkthrough
• Live Q&A with SAPPER experts
• See your own drawings analyzed (optional)
• Get personalized workflow recommendations

Why Builders & Architects Choose SAPPER

⚡ 95% Faster Than Manual

"Used to take me 4 hours to extract measurements and calculate thermal bridges. SAPPER does it in 10 minutes. Absolute game-changer."

- James P., SAP Assessor

💰 Saves £2,000+ Per Year

"No more paying £150/month for Elmhurst. SAPPER does everything I need for free. Saved my practice thousands already."

- Sarah M., Architect

✅ 100% Part L Compliant

"Building Control accepted every SAPPER report I've submitted. The calculations are spot-on and professionally formatted."

- Mark T., Builder

Don't Want to Wait for a Demo?

SAPPER is completely free and ready to use right now. No setup, no training, no credit card required.