| Approved Document F provides guidance on complying with the requirements of Regulation F dealing with the ventilation of buildings. It is a revised document which came into force on 1st April 2006. This guide is aimed at clarifying the documents contents for Local Authority Building Control customers.
Background ventilators and intermittent extract fans (System 1)
The ventilation strategy for dwellings adopted in the Approved Document F includes three main elements that can be delivered by natural or mechanical systems, or a combination of both:-
- Extract ventilation - mechanical extract for rooms with water vapour or pollutants.
- Whole building ventilation - providing fresh air and dispersal of pollutants through air exchange via background (trickle) ventilators.
- Purge ventilation - (previously called ‘rapid’) to remove large amounts of pollutants and vapour and to be used to improve thermal comfort.
Location of extract ventilation devices in rooms
- Cooker hoods should be 650 to 750mm above a hob surface
- Extract fans should be as high as possible, preferably not more than 400mm from the ceiling.
- Fans should be sited in each ‘wet room’.
- For a room with no openable window, the fan should have a 15 minute overrun. In rooms with no natural light, the fan could be controlled by the operation of the main room light switch.
Extract ventilation rates
| Room |
Minimum intermittent extraction rate |
| Kitchen |
30 l/s (adjacent to hob) or 60 l/s (elsewhere) |
| Utility room |
30 l/s |
| Bathroom |
15 l/s |
| Sanitary accommodation |
6 l/s (but can be purge ventilated) |
Background ventilators for dwellings
- For dwellings with more than one exposed façade the total equivalent area is given in the table overleaf. If there is only one, additional low level ventilators will be needed.
- All habitable rooms should have a minimum of 5,000 mm² and all ‘wet rooms’ with an external wall should have a minimum 2,500 mm² and should be typically 1.7m above floor level.
- To ensure good transfer of air throughout the dwelling there should be an undercut of minimum area 7,600mm² in all internal doors above the floor finish ( 10mm gap on a standard door).
- For single storey dwellings (flats) up to four storeys above ground add an additional 5,000mm².
Equivalent ventilator area for dwellings,(mm²)
| Total floor area (m²) |
Number of bedrooms |
| 1 |
2 |
3 |
4 |
5 |
| ≤50 |
25,000 |
35,000 |
45,000 |
45,000 |
55,000 |
| 51 - 60 |
25,000 |
30,000 |
40,000 |
45,000 |
55,000 |
| 61 - 70 |
30,000 |
30,000 |
35,000 |
45,000 |
55,000 |
| 71 - 80 |
35,000 |
35,000 |
35,000 |
45,000 |
55,000 |
| 81 - 90 |
40,000 |
40,000 |
40,000 |
45,000 |
55,000 |
| 91 - 100 |
45,000 |
45,000 |
45,000 |
45,000 |
55,000 |
| >100 |
Add 5,000 mm² for every additional 10 m² floor area |
Purge ventilation
Adequate purge ventilation may be achieved by the use of openable windows and/or external doors of the following sizes:-
- A hinged or pivot window that opens 30° or more, or sliding sash window where the height width of the opening area is at least 1/20th of the floor area of the room.
- A hinged or pivot window that opens less than 30°, the height × width of the opening area is at least 1/10th of the floor area of the room.
- An external door (including patio doors) that has an opening area at least 1/20th the floor area of the room.
Accessible controls
 Where manual controls are provided they should be within reasonable reach of occupants and it is recommended that they are located in accordance with the guidance for Requirement N3 Safe opening and closing of windows.
Windows, skylights and ventilators should have manual controls that are not more than 1.9m above floor level or 1.7m if there is an obstruction such as a sink or worktop.
Alternative ventilation systems are shown in the approved document and include Passive Stack, Continuous Mechanical Extract and Mechanical Supply with Heat Recovery (MVHR).
Replacement windows
All replacement windows should include trickle ventilators or an equivalent background ventilation opening in the same room. Where there was none before then there is no need to include them with the replacement windows.
Although not required by regulations, background "trickle" vents totalling 5,000mm² for habitable rooms and 2,500mm² for wet rooms will enable your building to breathe without breaching security.
Please also refer to Customer Information Sheet 30 for additional details in respect of replacement windows.
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