Trades master copy
Last reviewed: March 2026
What Part F is
Part F is the ventilation part of Building Regulations. For dwellings it covers extract fans, trickle vents, whole-house systems (MEV/MVHR), and making sure homes don't end up damp and stuffy - especially now we're sealing them up to hit Part L.
The 2021 edition (in force from June 2022) tightened everything up: higher whole-dwelling ventilation rates, more emphasis on background ventilation, and clearer rules for refurb jobs like new kitchens, bathrooms and window replacements.
This guide is a summary to make Part F easier to use on site. It does NOT replace Approved Document F - Volume 1: Dwellings (2021 edition) or the Domestic Ventilation Compliance guidance now folded into it.
You must read and follow the full Approved Document F and any manufacturer's design data for fans/MVHR units.
This guide is written for England. Wales, Scotland and Northern Ireland have their own versions of building regulations - the principles are similar but the documents and approval routes differ, so check local requirements if you're working outside England.
Where it applies on your jobs
Part F hits a lot of day-to-day work:
- New-build houses and flats - you must provide adequate extract, whole-dwelling ventilation and purge ventilation, and commission/test any mechanical systems.
- Kitchen and bathroom refurbs - replacing or adding extract fans now has to meet the new extract rates and commissioning requirements.
- Window replacements - just like Part L, swapping windows can't make ventilation worse; trickle vents or other background ventilators are often required in new frames.
- Energy-efficiency works - adding insulation or making a home significantly more airtight (e.g. re-render, EWI, new airtight windows) can trigger a need to improve ventilation.
Volume 1 is for dwellings; Volume 2 is for other buildings. Most small builders will live in Volume 1 almost all the time.
Key "trigger points" - what actually matters on site
The bits that changed in 2022 and now catch people out:
Extract ventilation in "wet rooms"
- Kitchens, utility rooms, bathrooms and WCs all need effective extract (intermittent or continuous) that meets the minimum litres/second in AD F.
- When you refurb a kitchen or bathroom, the new fan must meet current rates and be commissioned - you can't just "match what was there before".
Background ventilation (trickle vents etc.)
- New rules expect background ventilators in habitable rooms and kitchens for naturally ventilated homes, sized by equivalent area per room (e.g. around 8,000-10,000 mm² in many cases, 4,000 mm² in bathrooms, plus minimum numbers of vents per dwelling).
- When replacing windows, you generally need to replace existing trickle vents with equivalent or better, and add them if the new windows would otherwise make ventilation worse.
Whole-dwelling ventilation rates
- Increased minimum whole-dwelling ventilation rates (l/s) based on floor area and number of bedrooms.
- If you're on MEV/MVHR, the system design and commissioning must show it meets these rates, not just "fan on the wall".
Commissioning and testing
- Mechanical ventilation systems (MEV/MVHR, and in practice often dMEV) must be commissioned, with measured flow rates recorded and handed to Building Control and the client.
- You can't just install fans and walk away - there has to be a commissioning sheet.
Purge (rapid) ventilation
- Every habitable room must have a way to purge - usually openable windows big enough to meet the minimum opening area from Part F.
- On tight urban sites or with fixed glazing, this needs thinking about at design stage.
Quick reference table - common jobs
New kitchen in existing house
- Fit an extract that meets the current rate (e.g. higher l/s if continuous, defined intermittent rate if on a boost-only fan).
- Make sure there is still adequate background ventilation (trickle vents or wall vents) and purge via an opening window.
New bathroom or shower room
- Provide an extract fan to current spec (often continuous or timed-overrun) meeting the AD F rate.
- Provide background ventilation (trickle vent or similar) unless the overall design justifies another solution.
- Commission the fan and hand over settings and instructions.
Replacing all windows in a house
- New windows must not reduce background ventilation:
- Replace existing trickle vents with equivalent or better.
- Add vents where needed if new, tighter windows would otherwise worsen ventilation.
- Check the number and size of vents per habitable room and per dwelling against AD F tables.
New-build house with MEV or MVHR
- System must be designed to meet whole-dwelling and room-by-room rates.
- Duct routes, silencers, and access for maintenance must follow the design and manufacturer's instructions.
- Commission, measure flow rates, set up controls, and give the client the documentation.
Big insulation/airtightness upgrade to existing house
- If you're significantly tightening up the building fabric (EWI, new airtight windows, internal insulation), you may need to upgrade ventilation too so you don't create condensation and mould problems.
- Part F expects that energy efficiency works should not make ventilation worse - in some cases that means adding trickle vents or mechanical extract.
Routes to compliance for trades
No registration scheme here either - success is about following the right "system type" and documenting it:
Use the standard ventilation "systems" from Approved Document F
- Natural ventilation: intermittent extract fans + trickle vents + purge via windows.
- Continuous mechanical extract (MEV/dMEV): continuous extract fans, with background ventilators, sized to AD F rates.
- Mechanical ventilation with heat recovery (MVHR): balanced system meeting both supply and extract rates.
Size and select kit to the new 2021/2022 rates
Don't just fit a 15-year-old spec 85 m³/h fan by habit - check the minimum l/s for that room and type of system in the latest tables.
Remember noise and usability: if the fan is so noisy they switch it off at the isolator, you've lost compliance in practice.
Commission everything that moves air
Set speeds, measure flow rates, and record them. Use the manufacturer's commissioning sheets or your own that cover the AD F requirements.
Give the paperwork to Building Control and to the client with simple operating instructions.
Treat window replacements and refurb kitchens/bathrooms as Part F jobs
On windows, plan vent locations and sizes with the supplier; don't wait until frames are made.
On kitchens/bathrooms, upgrade fans to current spec and ensure there's background and purge ventilation, not just a shiny new cooker hood.
Who is responsible for what
On a typical domestic project:
- The designer (architect/MEP designer) should specify the ventilation strategy: system type (natural/MEV/MVHR), fan rates, locations, duct routes, and required trickle vent areas.
- The builder/main contractor is responsible for actually fitting the specified kit, not swapping fans or windows to cheaper options without checking Part F impact.
- The electrician and ventilation installer are responsible for correct wiring, ducting, commissioning and labelling fans and systems to manufacturer and AD F guidance.
- The window installer is responsible for ensuring trickle vents/background ventilators are installed and sized correctly where required.
- The client/owner lives with the result - stuffy rooms, condensation and mould, or a compliant, healthy house.
Same blunt truth as with the other Parts:
If you're running the job and you drop the spec on fans or windows because "the client doesn't want trickle vents" or "that MVHR looks pricey", that's your problem when Building Control or the occupants come back with damp and mould.
Simple rule to drum into your team
If you're touching kitchens, bathrooms, windows, or doing anything that makes the building more airtight, treat it as a Part F job. Check extract rates, background vents and whole-house ventilation before you sign off.
On-site checklist (Part F)
Before you start
- Confirm the ventilation system type for the dwelling (natural, MEV/dMEV, MVHR).
- Get the latest schedule showing required fan rates, vent sizes and positions.
- For window jobs, agree trickle vent requirements with the designer/supplier up front.
While you're working
- Install fans, ducts and vents exactly as per drawings and manufacturer details - short, straight ducts, correct diameters, no crushed flexible ducting.
- Fit trickle vents/background ventilators in the correct locations and numbers per room.
- Keep penetrations well sealed to avoid uncontrolled air leakage bypassing the system.
When you finish
- Commission fans and systems: set speeds, measure flow rates, and record them.
- Check every habitable room has a purge route (openable window/door) and the expected background ventilation.
- Hand over user instructions and commissioning sheets to the client and Building Control.
Sources
Based on:
- Approved Document F: Ventilation - Volume 1: Dwellings (2021 edition, effective June 2022).
- Government and industry summaries of the 2022 Part F changes for dwellings (ventilation systems, trickle vents, rates and commissioning).
- Practical guidance on how Part F affects kitchens, bathrooms, window replacement and airtightness/retrofit work.
This guide was last reviewed March 2026. SiteKiln does not provide legal, financial or tax advice. All content is for general information purposes only. Always seek professional advice for your specific situation.
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Working in Wales? The building rules are different. See our Working in Wales guides.
Working in Scotland? Building standards work differently. See our Working in Scotland guides.
Working in Northern Ireland? The system uses Technical Booklets. See our Working in Northern Ireland guides.
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