Part O simplified method

Free interactive checker for Approved Document O (Overheating), simplified method, England (2021 edition). This tool is for guidance only.

Want us to do this for you? We can run the Part O simplified method and issue a clean output for £50 + VAT. If the simplified method is not appropriate, or it fails, we can provide a TM59 dynamic thermal model from £350 + VAT.

Why TM59? It is the recognised overheating methodology for new homes. It uses dynamic simulation, so it can account for shading, ventilation strategy, thermal mass and weather in a way fixed-percentage checks cannot.

Tip, if external noise or pollution prevents windows being opened, the simplified method is usually not suitable. This tool will flag that and explain next steps.

Project details
Simplified method inputs
Use the help buttons for definitions and what to enter. The tool uses a discharge coefficient method to convert opening geometry into equivalent area.
Window and door data
Add one row per pane. Include fixed panes as well, as they still contribute to glazing area. Only panes marked as opened for removal of excess heat count towards purge ventilation.
Bedroom night ventilation only counts where the opening can be left safely open overnight. If a bedroom window is easily accessible and not secure, the night-time equivalent area will be zero.
Results breakdown
How to read this. The simplified method checks (1) limiting solar gains, (2) removal of excess heat, plus (3) bedroom night-time ventilation. A fail here does not automatically mean the scheme cannot comply, it often means you need either design changes or a TM59 assessment.

Key context

Largest glazed façade orientation
N/A
Total floor area used in calculation (m²)
0
Total glazing area (m²)
0

Limiting solar gains

Check Actual Target Result
Total glazing, % of floor area 0% 0% N/A
Most glazed room, % of room floor area 0% 0% N/A
Shading requirement N/A N/A N/A

Removal of excess heat, purge ventilation

Check Actual Target Result
Total equivalent area, % of floor area 0% 0% N/A
Total equivalent area, % of glazing area 0% 0% N/A
Total equivalent area (m²) 0 - N/A

Bedrooms, night-time ventilation

Need a formal output? If you want us to run this for you, email us the drawings and window schedule and we can issue a clean output for £50 + VAT. If it fails, or if noise and pollution make the simplified method unsuitable, TM59 is usually the right next step, from £350 + VAT.
Disclaimer, this tool is provided as-is with no warranty. Outputs depend entirely on what you enter. Always cross-check against the latest Approved Document O and Building Control requirements for your project.