Ventilation near you

Approved Document F sets out system-specific guidance for three approaches, and the choice depends heavily on how airtight the dwelling is. Getting this wrong is why some retrofitted homes feel stuffy and damp despite new fans.

Extract ventilation to the outside should be provided in kitchens, utility rooms, bathrooms and sanitary accommodation, and it can be intermittent or continuous. For intermittent systems, Approved Document F Volume 1 sets minimum extract rates in litres per second: 30 for a kitchen where a cooker hood extracts to the outside, 60 for a kitchen with no cooker hood or where the hood does not extract outside, 30 for a utility room, 15 for a bathroom and 6 for sanitary accommodation, with the purge ventilation guidance available as an alternative for sanitary accommodation.

Continuous systems are specified differently, with a minimum high rate of 13 litres per second for a kitchen, 8 for a utility room, 8 for a bathroom and 6 for sanitary accommodation, and a continuous rate such that the sum of all extract in the dwelling is at least the whole dwelling ventilation rate.

That whole dwelling rate has two parts, both of which have to be met: a minimum of 0.3 litres per second for each square metre of internal floor area counting all storeys, and a minimum set by bedroom count, which runs 19 litres per second for one bedroom, 25 for two, 31 for three, 37 for four and 43 for five, adding 6 for each additional bedroom. A dwelling with only one habitable room uses 13 litres per second.

Background ventilators, the small controllable openings usually built into the window head, are how supply air reaches habitable rooms in a naturally ventilated house. Approved Document F sizes them by equivalent area in square millimetres rather than free area, and expects that equivalent area to be marked where it is easy to see from inside the dwelling so building control can verify it.

Replacing windows is the moment this is most often lost, which is why Approved Document F addresses it directly. Where the existing windows have background ventilators, the replacements should include them too, no smaller than those in the original window and controllable either automatically or by the occupant. Where the old windows had none, the replacement is likely to increase the airtightness of the dwelling, and the ventilation provision must end up no worse than before the work.

The guidance gives concrete sizes for that case: background ventilators in the replacement windows with a minimum equivalent area of 8,000 square millimetres in habitable rooms, 8,000 in a kitchen and 4,000 in a bathroom with or without a toilet. Where the dwelling will have continuous mechanical extract ventilation instead, the figure is a minimum of 4,000 square millimetres in each habitable room for replacement windows outside wet rooms. These editions of Approved Document F came into force on 15 June 2022 in England.

The signs of an under-ventilated home are consistent: windows streaming in the morning, a bathroom that stays damp for hours, musty smells in cupboards on outside walls, and black mould returning in the same corners after every clean. Government guidance describes condensation, the most common form of damp, as moisture generated inside the home cooling and condensing onto colder parts of the building.

The same guidance is blunt about cause and blame: it states that it is totally unreasonable to blame damp and mould in the home on lifestyle choices, and locates the fundamental cause in building deficiencies, inadequate ventilation, inadequate heating and/or poor energy efficiency. Cooking, washing and breathing produce moisture in every household; the question is whether the building can deal with it.

The health case for fixing it is serious. That guidance notes that the respiratory effects of damp and mould can cause serious illness and, in the most severe cases, death, and lists those most at risk, including people with pre-existing respiratory conditions or weakened immune systems, children, older people, pregnant women and those in fuel poverty. It recommends that kitchens have extractor fans or cooker hoods that are fully operational and sufficiently powered, and that bathrooms have ventilation systems such as extractor fans, suggesting humidity-controlled fans and fans linked to the light switch with an over-run.

Approved Document F states that building work should not reduce the ventilation provision of a dwelling unless the provision afterwards still meets the minimum standards. For energy efficiency work it offers a simplified method: measures are counted as major or minor, from loft and cavity insulation to sealing a suspended floor or blocking a chimney, and the combination puts the job in Category A, B or C. Category A suggests no further ventilation is needed; Categories B and C indicate the provision has likely fallen below requirement and further ventilation should be added, by natural means, continuous mechanical extract or heat recovery.

Some work is lighter touch than people expect. Approved Document F notes that replacing an extractor fan or cooker hood using the existing cabling does not need to be notified to a building control body, while GOV.UK explains that you do not need to seek approval yourself if you use an installer registered with a competent person scheme. Where a wet room is added to an existing dwelling, extract must be provided along with a background ventilator of at least 5,000 square millimetres equivalent area, unless continuous extract or a single-room heat recovery ventilator is used.

Devolution matters here. Scotland's system under the Building (Scotland) Act 2003 runs on a building warrant before work begins and a completion certificate before occupation, with the domestic technical handbook covering ventilation in Section 3 and energy in Section 6. In Northern Ireland, the Building Regulations (Northern Ireland) 2012 deal with ventilation in Part K, so quoting English part letters to a Belfast building control officer will not get you far.

Ventilation needs change with the season, and the winter instinct to shut everything is what starts most condensation problems. Background ventilators are designed to stay open in normal use, and government guidance on ventilating homes advises checking that trickle vents or grilles are open and not blocked, noting that opening windows and doors is the simplest way of improving ventilation for most people and that windows do not need to be open all the time to be effective. It also points to keeping rooms at least 18 degrees Celsius for older people and those with health conditions, which is why ventilation and heating have to be considered together rather than traded off.

Summer is now a regulated concern for new homes. Part O covers overheating mitigation, and Approved Document O applies to new residential buildings, working through limiting unwanted solar gains and removing excess heat, using passive means as far as reasonably practicable. It does not apply to existing homes, to retrofits, or to extensions and conservatories added to residential buildings after they are built. Where mechanical cooling is used in a new building, the designer has to demonstrate to the building control body that all practicable passive means have also been incorporated.

A ventilation system is only as good as its upkeep: vents left open and clear, filters changed on the manufacturer's schedule, grilles washed, and fans checked occasionally to confirm they still move air rather than merely make noise. The installer is required to give the owner sufficient information about the system and its maintenance requirements so it can be operated to provide adequate ventilation, and that written guidance is worth keeping with the property's paperwork.

When it is time to bring someone in, LokalMatch lets you describe the problem once, with the rooms affected, the age and type of the property and what has already been tried, and matched local professionals reach out to you. Pros pay to receive those requests, which is how LokalMatch makes its money. The service does not carry out ventilation work, does not set the price of any job, and does not vet, rank or recommend the pros who respond, so ask each one how they will measure the resulting air flow rates.