About the Part O Calculator
Professional overheating-risk assessment for UK Building Regulations, built by industry experts for architects, assessors, and developers.
What this app does
The Part O Calculator is a specialist compliance tool that helps you assess residential dwellings against Approved Document O (2021) - the section of the UK Building Regulations that addresses overheating mitigation in new homes. The application runs the official Simplified Method set out in AD-O Tables 1.1 and 1.2, checking your dwelling's glazing-to-floor ratios against the maximum allowable percentages for its risk zone, orientation, and cross-ventilation status.
You can run a Quick Assessment using whole-dwelling facade inputs, or a Detailed Assessment that evaluates compliance room-by-room - including individual bedroom checks and per-facade limits. Drawings can be uploaded and scaled directly inside the app, with AI-assisted window detection to speed up the glazing take-off. Every assessment produces a formal PDF report ready for submission to Building Control, complete with site location, regulatory references, room schedules, and an assessor certification block.
Behind the scenes, the calculator references the same risk-zone classifications, Tables 1.1/1.2 limits, and orientation rules used by approved inspectors, so the results you produce mirror the methodology a Building Control body would apply.
Who it's for
Architects & Designers
Test glazing strategies early in the design process and avoid costly redesigns at planning or building-control stage.
Building Control Assessors
Issue formal compliance reports with consistent methodology, room schedules, and certification blocks.
Energy Consultants
Add Part O assessments alongside Part L, SAP, and ventilation services using a single, auditable workflow.
Developers & Self-Builders
Understand whether your project will pass the Simplified Method before committing to glazing specifications or seeking a dynamic thermal model.
Who builds it
The Part O Calculator is developed and maintained by EnvirAssist UK, an independent practice specialising in UK Building Regulations compliance - including Part L (energy efficiency), Part G (water consumption), Part F (ventilation), and Part O (overheating). The team behind this tool has delivered compliance assessments and dynamic thermal modelling for hundreds of UK residential projects.
The application is part of a family of regulatory tools that includes SAPPER (Part L extensions), Part G (potable water), HIA (planning health impact assessments), and HEAES (alternative energy systems) - all designed to make UK compliance work faster, more transparent, and more reliable.