Approved Document F, the ventilation section of the building regulations, came into force on 15 June 2022, according to the consumer body Which?1. The rules require extra ventilation in habitable rooms when over 30% of a property's windows are replaced1.
The requirement applies to living rooms, dining rooms, bedrooms, kitchens and bathrooms, which the regulations treat as habitable rooms1. The stated reason is that new windows are likely to be more airtight than the ones they replace, preventing fresh air from entering1.
The rules distinguish between two ways of getting fresh air into a home: purge ventilation, which means opening doors and windows, and background ventilation, which allows fresh air in at a low level continuously1. The new regulations require background ventilation1. Which? lists several methods: window trickle ventilators, described as holes drilled through the window frame with external and internal covers, a cheap but visually intrusive option with poorer energy efficiency than other methods; passive wall ventilation, a small hole in the wall needing no power supply; positive input ventilation, which pushes filtered fresh air into a room; and mechanical heat recovery ventilation, a whole house system using a heat exchanger, described as effective but expensive1.
"The new regulations require extra ventilation to be provided to habitable rooms - living rooms, dining rooms, bedrooms, kitchens and bathrooms - when over 30% of the property's windows are replaced. This is because new windows are likely to be more airtight, preventing fresh air from entering."
Which? notes that good ventilation helps reduce condensation and damp1. The same article sets out the separate energy performance rules for replacement windows: windows are rated between A++ and E under a system run by the British Fenestration Rating Council, and building regulations require all new windows to be at least C-rated1. It also reports Energy Saving Trust figures that replacing all single-glazed windows in a detached house with A++ double glazed windows could save up to £175 per year, and £60 in a mid-terraced house1.
Why it matters for households
Replacement windows are one of the main ways a home loses less heat, but the same airtightness that reduces draughts also reduces the accidental fresh air that older, leakier windows provided. Approved Document F addresses that trade-off by requiring a permanent, low-level air path in habitable rooms once a replacement project crosses the 30% threshold. For a household, the practical effect is that a window replacement is no longer only a glazing decision: it also brings a ventilation decision, and the method chosen affects how visible the vents are, whether they need power, and how much they cost. The rules sit alongside the energy performance requirements for new windows, so a replacement project is assessed on both ventilation and thermal performance. Households weighing up replacement windows rules and building control sign-off can read the site's guide to Building Regulations Part F: ventilation requirements, which covers the same threshold, and the guide to trickle vents when replacing windows. Because ventilation and insulation interact, the wider context is set out in home ventilation and Building Regulations Part L. Homes in Wales and Scotland are covered by separate regimes, described in Welsh building regulations for insulation and glazing and Scottish building standards for insulation, glazing and ventilation. Where ventilation is inadequate after airtightness work, the symptoms are covered in why is my home damp and mouldy after insulation and double glazing.
What happens next
The sources do not report any further dated steps, reviews or transitional arrangements for Approved Document F. Which? records the commencement date of 15 June 2022 and the 30% threshold, and does not state what happens to projects already under way at that date1.
Sources1 cited
- What to look for when buying double glazing - Which?, which.co.uk