Purge ventilation opening area

One twentieth (1/20) of the floor area of the room for a hinged or pivot window opening 30° or more

Habitable room ventilated by openable windows

Every figure for this topic is on one page: Roof void ventilation, access and fire compartmentation

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Openable area required for purge ventilation, expressed as a proportion of the floor area of the room.

Basis in regulation

Part F
Approved Document F
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How to check it on site

Work the openable area out per room from the window schedule at design stage, then confirm the opening angle achieved on site.

Common failure

Restrictors fitted for safety that reduce the opening angle below the assumption used in the calculation.

Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

Related dimensions at this stage

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225 mm

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25 mm

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300 mm

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6 °C

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75 mm for baths, basins, sinks and showers on a branch; 50 mm for a WC trap

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Stair Handrail Height and Clearance

600 mm

A handrail is mandatory for flights of stairs where the rise exceeds 600mm