• Description

Ventilation of rooms

The correct ventilation of a room is important if condensation problems are to be avoided. The guide below gives the minimum requirements for each room type.

Room(1) Rapid ventilation opening(s) (minimum free area) Background ventilation opening(s)(2) (minimum free area) Mechanical extract ventilation(3)(4) (nominal airflow rates)
Habitable room 1/20th of floor area 8000 mm2  
Kitchen(5) 1/20th of floor area 4000 mm2 30 litres/second adjacent
to a hob(6) or 60 litres/
second elsewhere
Utility room 1/20th of floor area 4000 mm2 30 litres/second
Bathroom (with or without WC) 1/20th of floor area 4000 mm2 15 litres/second
Sanitary accommodation
(separate from bathroom)
1/20th of floor area(7) 4000 mm2  

  1. Notes to Table
    Where a room serves a combined function such as a kitchen-diner, the individual provisions for rapid, background and mechanical extract ventilation need not be duplicated provided that the greater or greatest provision for the individual functions in Table 2.1 is made.
  2. As an alternative to the background ventilation provisions listed in Table 2.1, background ventilation openings equivalent to an average of 6000 mm2 per room may be provided but no room shall have a background ventilation opening of less than 4000 mm2.
  3. ) As an alternative to mechanical extract ventilation, passive stack ventilation may be provided. Where passive stack ventilation is provided it shall be designed and constructed in accordance with BRE Information Paper 13/94 or a valid BBA Certificate.
  4. Mechanical extract ventilation shall not be provided in a room where there is an open-flued solid fuel burning appliance (see paragraph 1.4). Mechanical extract ventilation (or passive stack ventilation) need not be provided in a room with an open-flued appliance which has a flue having a free area at least equivalent to a 125 mm diameter duct and the appliance’s combustion air inlet and dilution air inlet are permanently open when the appliance is not in use.
  5. This provision is for a domestic size kitchen where the appliances and usage are of a domestic nature. Guidance on the ventilation required for commercial kitchens is given in CIBSE Guide B, Tables B2.3 and B2.11.
  6. Adjacent to a hob means either –
    (a) incorporated within a cooker hood located over the hob; or
    (b) located near the ceiling within 300 mm of the centreline of the space for the hob.
  7. As an alternative, mechanical extract ventilation at 6 litres/second may be provided.

Please check with your local building control department before using information contained in this page to ensure that they comply with your local building codes.