Intermittent extract rates by room

Kitchen 30 l/s next to the hob or 60 l/s elsewhere; utility room 30 l/s; bathroom 15 l/s; WC 6 l/s

Intermittent mechanical extract in a wet room

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

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Minimum intermittent extract ventilation rate for each wet room in a dwelling.

Basis in regulation

Part F
Approved Document F
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How to check it on site

Measure with an anemometer at the terminal, not the fan, and record the reading per room for the commissioning sheet.

Common failure

A fan rated at the correct rate but ducted through long flexible runs and tight bends, so the measured flow falls short.

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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Hearth Provision and Floor Finishes

225 mm

A hearth may not be necessary if an appliance's flame or incandescent material is positioned at least 225mm above the floor

Minimum

Soundproofing Measures for Soil Pipes

25 mm

Sound insulation for soil pipes involves either encasing them in boxing made from a material with a minimum mass of 15kg/m², or wrapping them with at least 25mm of unfaced mineral wool, typically 10kg/m³ density

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Electrical Accessory Clearance from Water Diagrams

300 mm

Diagrams illustrating the required 300mm minimum horizontal clearance for electrical accessories from water sources, such as sinks and wash basins, are commonly used in guidance documents

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Conditions for Pipe Freezing Calculations

6 °C

Calculations for pipe insulation to prevent freezing are based on specific assumed conditions, typically including an external air temperature of -6°C and an internal water temperature of +7°C

Minimum

Water seal depth at appliance traps

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

Appliance trap on a branch discharge pipe

Minimum

Stair Handrail Height and Clearance

600 mm

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