What does the simplified Part O check cover?

It screens glazing area and openable area against AD O limits for dwellings in moderate and high-risk locations — not a full dynamic thermal model.

When is a full TM59 or dynamic simulation required?

High-risk developments, complex facades, or where the simplified method fails require dynamic overheating analysis per the project compliance route.

How do I determine if my site is high risk?

AD O maps and criteria classify locations. Urban heat island, orientation, and glazing ratio all affect the assessment path.

BuildFlo Design Guide · Thermal · Approved Document O

Part O simplified overheating assessment

Simplified Approved Document O check for glazing limits and opening areas in UK dwellings. Free Part O overheating calculator.

What this calculator does

Part O assessment helps UK building services engineers with simplified ad o check for glazing limits and opening areas in dwellings. The calculation follows Approved Document O methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "part o assessment", "part o assessment calculator", or "how to part o assessment", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Part O assessment calculator

Simplified AD O check for glazing limits and opening areas in dwellings

Cross-ventilation criteria met

Does the dwelling meet AD O cross-ventilation criteria?

Overheating risk locationLargest glazed façade orientationTotal floor area (m²)Total window area (m²)Average opening area (% of window) (%)

Free opening area as % of total window area for the dwelling (building-level check)

Living room floor area (m²)Living room window area (m²)Living room opening % (%)Kitchen floor area (m²)Kitchen window area (m²)Kitchen opening % (%)Other room floor area (m²)Other room window area (m²)Other room opening % (%)Bedroom 1 floor area (m²)Bedroom 1 window area (m²)Bedroom 1 opening % (%)Bedroom 2 floor area (m²)Bedroom 2 window area (m²)Bedroom 2 opening % (%)Bedroom 3 floor area (m²)Bedroom 3 window area (m²)Bedroom 3 opening % (%)Bedroom 4 floor area (m²)Bedroom 4 window area (m²)Bedroom 4 opening % (%)

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Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about part o assessment under UK standards.

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Frequently asked questions

What does the simplified Part O check cover?: It screens glazing area and openable area against AD O limits for dwellings in moderate and high-risk locations — not a full dynamic thermal model.
When is a full TM59 or dynamic simulation required?: High-risk developments, complex facades, or where the simplified method fails require dynamic overheating analysis per the project compliance route.
How do I determine if my site is high risk?: AD O maps and criteria classify locations. Urban heat island, orientation, and glazing ratio all affect the assessment path.