In this guide
- What Part F covers and where it applies
- The three layers of ventilation
- The four ventilation systems in Approved Document F
- Ventilation rates for dwellings
- When work on an existing home triggers Part F
- Testing, commissioning and records
- What changes in 2027
- Part F across the UK nations
- How ventilation connects to damp and mould
- Perspective
- Get the ventilation assessed properly
- FAQ
- Sources
Ventilation in UK buildings is governed by Part F of the Building Regulations. In England, the technical guidance sits in Approved Document F: Volume 1 covers dwellings and Volume 2 covers buildings other than dwellings. The core rule is short: there must be adequate means of ventilation for people in the building. The detail is in how that is achieved: extract in wet rooms, a background supply of fresh air, and a way to purge air quickly. A revised document has been published, and its dwellings volume takes effect in 2027.
This guide sets out what Part F asks for in homes, how the four ventilation systems work, what applies when windows or fans are replaced, and how ventilation links to damp and mould.
Key Takeaways
- Part F applies in England. Wales, Scotland and Northern Ireland each run their own rules and timelines, because building regulations are devolved.
- Approved Document F (2026) was published on 24 March 2026. The dwellings volume takes effect on 24 March 2027 for most building work. Earlier versions still apply to work under earlier standards.
- A dwelling needs extract ventilation in wet rooms, whole-dwelling ventilation for fresh air, and purge ventilation for occasional high moisture or pollutant levels.
- Replacing windows or fans in an existing home triggers ventilation standards, or at minimum a requirement that provision is no worse than before.
- Poor ventilation is a common root cause of condensation and mould, so a survey should look at airflow as well as the visible damp.
What Part F covers and where it applies
Part F of Schedule 1 to the Building Regulations 2010 sets the ventilation requirement for buildings in England. The guidance on meeting it is Approved Document F. Volume 1 applies to dwellings. Volume 2 applies to everything else, such as offices, shops and commercial premises.
Requirement F1(1) is one sentence: there shall be adequate means of ventilation provided for people in the building. It does not apply to spaces people do not normally enter, spaces used solely for storage, or a garage used solely with a single dwelling.
Approved documents are guidance, not law in themselves. Following them is the usual way to show compliance, and building control bodies treat them as the benchmark.
What a compliant dwelling must do
According to Volume 1, a dwelling meets F1(1) when it:
- extracts water vapor and indoor air pollutants where they are produced in quantity, such as kitchens, utility rooms and bathrooms
- supplies a minimum level of outdoor air for occupants’ health
- rapidly dilutes pollutants in habitable rooms
- limits the entry of external pollutants
- keeps noise low, allows easy maintenance access and protects occupants from cold draughts
Those points are drawn from Approved Document F Volume 1. The practical effect is that ventilation has to be designed as a whole, not as a single fan in the bathroom.
Buildings other than dwellings
Volume 2 follows the same logic with some additions. Per Volume 2, such buildings must also monitor air quality in certain types of occupiable room and protect against rain entering through ventilation openings. Landlords and businesses with commercial units should check which volume applies to the work being planned.
The three layers of ventilation
The approved document’s strategy combines three elements. Extract ventilation, whole-building ventilation and purge ventilation each do a different job.
| Layer | Purpose | Typical provision |
|---|---|---|
| Extract ventilation | Removes moisture and pollutants at source | Fans or ducts in kitchens, bathrooms, WCs and utility rooms |
| Whole-dwelling ventilation | Supplies fresh air and dilutes pollutants continuously | Background vents, or continuous mechanical systems |
| Purge ventilation | Clears high concentrations occasionally | Openable windows or doors in habitable rooms |
Purge ventilation is not a substitute for the other two. It handles occasional events such as decorating or a burnt meal. Everyday moisture from showers, cooking and drying clothes needs a steady, controlled route out of the building.
The four ventilation systems in Approved Document F
Volume 1 recognizes four whole-dwelling strategies, as summarized in this compliance guide:
- System 1: background ventilators plus intermittent extract fans. This is the traditional approach.
- System 2: passive stack ventilation, which relies on thermal buoyancy and wind effect rather than fans.
- System 3: continuous mechanical extract ventilation (MEV), or decentralized MEV.
- System 4: mechanical ventilation with heat recovery (MVHR), which extracts and supplies air together and recovers heat from the outgoing air.
Which system suits which home
Airtightness decides much of the choice. Natural ventilation guidance suits only less airtight dwellings, which one compliance guide defines as a design air permeability above 5 m³/(h·m²) at 50 Pa, or an as-built figure above 3 m³/(h·m²). Tighter homes need continuous mechanical extract or MVHR.
For MVHR, the Part F guidance summarized by one manufacturer requires a minimum heat recovery efficiency of 73%, with extract and supply airflow balanced.
Most older homes in Dorset, Hampshire and Wiltshire are not airtight. Solid-walled Victorian terraces and period cottages usually fall within System 1 territory, with the added question of whether existing vents, fans and chimneys still work. Where airflow is weak, a positive input ventilation unit is one of the options a survey may consider for a specific property.
Ventilation rates for dwellings
The whole-dwelling rate must satisfy two tests at once. It must be at least 0.3 litres per second per m² of internal floor area, and it must meet the rate for the number of bedrooms in Table 1.3. The bedroom rates are 19 l/s for one bedroom, 25 for two, 31 for three, 37 for four and 43 for five, with 6 l/s added for each bedroom beyond five, as set out in the reference tables. The higher of the two results applies.
Extract rates by room
The same reference gives the minimum intermittent extract rates:
| Room | Minimum extract rate |
|---|---|
| Kitchen with cooker hood extracting to outside | 30 l/s |
| Kitchen with no cooker hood | 60 l/s |
| Utility room | 30 l/s |
| Bathroom | 15 l/s |
| WC | 6 l/s |
A kitchen is where ducting choices matter most. Long runs, tight bends and the wrong duct diameter cut real airflow well below the fan’s label rating. Our guide to kitchen ventilation options and ducting pitfalls covers this in detail, and the bathroom extractor fan upgrade guide does the same for wet rooms.
Where a room has no openable window, the fan needs controls that keep it running for at least 15 minutes after the room is vacated, according to paragraph 1.51 as cited in one guide. In practice that means a timer or humidity-controlled overrun.
Background ventilators
For natural ventilation, equivalent areas are 8000 mm² per habitable room and kitchen in multi-storey dwellings, 10,000 mm² in single-storey dwellings, and 4000 mm² for bathrooms, per the same rates reference.
When work on an existing home triggers Part F
Most homeowners meet Part F not through a new build but through a repair or upgrade. Volume 1 sets out two situations.
Ventilation work. Adding a habitable room or a wet room, or replacing part of the ventilation system including extract fans, should meet the relevant standards in Approved Document F.
Other work that affects ventilation. Replacing a window or door, or carrying out energy efficiency work, should either meet the standards or leave ventilation no less satisfactory than before.
Replacement windows and trickle vents
The rule for windows is specific. If the old windows had trickle vents, replacement windows should include controllable trickle vents no smaller than the originals. If they had none, provision must be no worse than before, which can be shown by fitting vents of at least 8000 mm² equivalent area in habitable rooms and kitchen, and 4000 mm² in bathrooms.
This matters for damp. Sealing an older home with new glazing, draught-proofing or insulation removes accidental air leakage that was quietly managing moisture. Without a planned replacement route, humidity rises and condensation follows. This is why our energy efficiency upgrades are assessed together with the ventilation the property needs.
Testing, commissioning and records
Mechanical ventilation must be proved to work as designed. For new dwellings, Volume 1 requires airflow testing of mechanical fans using a calibrated measurement device with a proprietary hood. The device must have ±5% accuracy and a calibration within the last 12 months at a UKAS-accredited centre. Results go to the local authority no later than five days after the final test. All of this is in paragraphs 4.23 to 4.25.
For existing dwellings, testing should be carried out on:
- new centralized mechanical ventilation systems, or major changes to existing ones
- new fans with ductwork longer than 2 m
- new fans connected to ductwork with more than one 90-degree offset
The person doing the work must also give the owner information about the system and its maintenance needs within five days of completion. Records matter more under the new regime: contractors and housing providers will need evidence that systems were commissioned correctly and airflow results passed on.
What changes in 2027
Approved Document F (2026) was published on 24 March 2026 by the Ministry of Housing, Communities and Local Government. Earlier versions continue to apply to buildings subject to previous standards. The 2026 Volume 1 takes effect on 24 March 2027 for building work not connected with higher-risk building work, and on 24 September 2027 for higher-risk building work. Transitional arrangements are in Circular Letter 01/2026.
If a project has been started or applied for under earlier rules, the transitional arrangements decide which version applies. Building control or the project’s designer can confirm this.
Part F across the UK nations
Building regulations are devolved, so Part F as described here is an England document. CIBSE Journal notes that Scotland, Wales and Northern Ireland manage their own frameworks and timelines. Scotland uses its Domestic Technical Handbooks. Wales published updated Approved Documents L and F on 7 April 2026.
The Welsh Volume 1 takes effect on 4 March 2027. It does not apply to work where a building notice, full plans application or initial notice was submitted before that date, provided work starts before 4 March 2028. Anyone with property across borders should check each nation’s own guidance.
How ventilation connects to damp and mould
The approved document states the health case plainly: without adequate ventilation, mould and internal air pollution might become hazardous to health. Condensation is the most common route. Warm, moist indoor air meets a cold surface, water forms, and mould follows on walls, window reveals and behind furniture.
The cause is not always ventilation. Rising damp, penetrating damp, leaking roofs and failed gutters produce similar stains, and treating the wrong cause wastes money. Homes with suspended timber floors add another factor: blocked air bricks and damp subfloors, covered in our guides to subfloor ventilation and damp and crawl space damp.
For homes with condensation-driven mould, the air quality improvement solutions we install are matched to what the diagnosis shows.
Perspective
Most ventilation problems we see are not a missing fan. They are a system that no longer matches how the building is used: a bathroom fan ducted too far, windows replaced without trickle vents, loft insulation added to a house that previously breathed through its fabric.
Part F gives a clear framework for new work, but older homes need a diagnosis first. Moisture readings, airflow checks and a look at how the property is lived in tell us whether the answer is extract fans, a PIV unit, a heat-recovery system, or a repair that removes the moisture source altogether.
All our diagnostic and remedial work is carried out by our own specialists rather than subcontractors, and every treatment carries a 25-year insurance-backed guarantee. We write down the root cause in a report, so the ventilation recommended is tied to evidence rather than guesswork.
Dylan
Get the ventilation assessed properly
Proofterior diagnoses and treats damp, mould and condensation in homes across Dorset, Hampshire and Wiltshire. A complimentary survey looks at moisture sources, ventilation and building fabric together, and the written report sets out the cause and the recommended treatment.
Book a complimentary property survey, or see the full range of damp, mould and ventilation services. Landlords, agents and property managers can use the same route for portfolio inspections.
FAQ
Does Part F apply to every UK home?
Part F applies to buildings in England. Wales, Scotland and Northern Ireland have their own regulations and timelines. Wales publishes its own Approved Document F, and Scotland uses its Technical Handbooks.
Do I need trickle vents in replacement windows?
If the old windows had trickle vents, the new ones should have controllable vents no smaller than the originals. If the old windows had none, ventilation must be no worse than before. Fitting vents of 8000 mm² in habitable rooms and the kitchen, and 4000 mm² in bathrooms, is one way to show this.
What extract rate does a kitchen need?
A kitchen with a cooker hood extracting to outside needs a minimum of 30 l/s. A kitchen without a hood needs 60 l/s. Ducting length and bends affect the airflow actually achieved, so installation matters as much as the fan rating.
Can a new extractor fan be fitted without building control involvement?
Replacing extract fans counts as ventilation work, which should meet Approved Document F. Testing is expected for new fans with ductwork longer than 2 m or more than one 90-degree bend. The installer must also give the owner system and maintenance information within five days.
Will better ventilation cure my mould?
Where condensation is the cause, improved extraction and background ventilation reduce the moisture that feeds mould. If the source is rising damp, a leak or penetrating water, ventilation alone will not fix it. A survey identifies which applies.
Sources
- Ventilation: Approved Document F, GOV.UK
- Approved Document F (2026), GOV.UK
- Approved Document F Volume 1: Dwellings (2026 edition)
- Approved Document F Volume 2: buildings other than dwellings
- Approved Document F Volume 1, Wales (2022)
- Approved Document F Volume 1, Wales (2026)
- CIBSE Journal: Ventilation design under the Future Homes Standard
- Part F ventilation rates reference
- Part F ventilation compliance guide
- The Building Regulations Part F, 2021 edition
- Approved Document F: ventilation requirements
- Installer Online: ventilation and the 2027 Building Regulation changes
