Do replacement windows need trickle vents? Part F, explained
A trickle vent is a small controllable slot vent in the window frame that provides constant background ventilation with the window shut. Since the 2021 update to Approved Document F (in force June 2022), replacement windows in England must normally provide background ventilation at least as good as the windows they replace, and where the old windows had no vents, habitable-room replacements are generally expected to include them.
Order vents with the window and they're supplied colour-matched and sized to your sashes, ready to fit at the sash head during installation, with the designer checking the vent physically fits each opener before you order.
What Part F actually requires
The rule for replacements is "no worse than before": if the outgoing windows had trickle vents, the new ones need at least the same equivalent area; if they didn't, guidance still expects new background ventilation in habitable rooms unless another ventilation strategy covers the room. Equivalent areas are measured in mm². Where the old windows had no vents, the usual figures in Approved Document F are 8000mm² for a habitable room or a kitchen and 4000mm² for a bathroom.
Compliance on a supply-only purchase sits with you or your installer, but the practical answer is simple: if in doubt, fit vents. Removing them later is impossible; adding them later means drilling your new frames.
The vents we offer
| Vent | Slot length | Equivalent area | Typical use |
|---|---|---|---|
| 2000EA | 300mm | 2,000mm² | Wet rooms and smaller requirements, one per opening sash |
| 4000EA | 400mm | 4,000mm² | Larger areas, two cover a typical habitable room's 8,000mm² |
Priced per opener in the designer; vents are colour-matched to your frame.
The designer checks the geometry for you: a vent needs the sash to be wide enough for its slot plus clearance, so it will only offer vent lengths that physically fit the openers in your current design, and it steps the vent down automatically if you narrow a sash below what the longer vent needs.
What trickle vents cost
The designer starts every window with trickle vents where they fit, priced per vent. Today, picking No trickle vents saves £10.00 on a 600 × 900mm Full Side Opener (£148.02 to £138.02) and £20.00 on a 1200 × 1200mm Classic Combination (£337.52 to £317.52), inc VAT. So that is what the vents add.
As standard, each window is: Full Side Opener, an opening window, 600 × 900mm overall, white inside and out, double glazed (28mm), clear glass, 150mm cill, trickle vents: 2000 (300mm), white handles, standard key-locking espag lock; and Classic Combination, an opening window, 1200 × 1200mm overall, white inside and out, double glazed (28mm), clear glass, 150mm cill, trickle vents: 2000 (300mm), white handles, standard key-locking espag lock. Each price opens the designer at that window. More options are priced in our window cost guide.
Prices include VAT at 20%. Delivery is extra: priced by straight-line distance from our factory (M28 2LY) to your postcode district, from £30, to mainland Britain addresses within 300 miles, not Northern Ireland, the Scottish Highlands or islands reached by ferry. Or collect free from the factory. Delivery and collection.
Do vents make windows draughty or noisy?
Modern vents are closable, baffled and sited at the frame head, so there's no perceptible draught at normal room heights. They exist to prevent the condensation and stale-air problems that sealed rooms develop. Acoustically a closed modern vent has little effect at typical suburban noise levels.
Frequently asked questions
- Are trickle vents a legal requirement on replacement windows?
- Since June 2022, replacement windows in England must provide background ventilation at least equivalent to what they replace, and habitable-room replacements are generally expected to include vents where none existed. The obligation to comply sits with whoever certifies the installation.
- My old windows had no vents. Do I need them now?
- Usually yes, for habitable rooms, unless the room's ventilation is provided another way (e.g. continuous mechanical ventilation). Ordering vents with the window means the right size arrives colour-matched with it, far better than retro-fitting a vent to a finished window later.
- How many vents does a room need?
- Guidance works in equivalent area: where the old windows had no vents, the usual figures in Approved Document F are 8000mm² for a habitable room or a kitchen and 4000mm² for a bathroom. One 4000EA vent provides 4000mm²; two openers with one each cover a habitable room.
- Can vents go on fixed windows?
- Our vents fit in opening sashes. A window with no openers takes a head vent in the frame where the design allows. The designer handles placement automatically.
- Can I close a trickle vent?
- Yes, every vent we supply has a closable flap, though Part F intends them to stay open in normal use to keep background air moving.
Sources
The official documents and schemes this page refers to. Rules change, so check the current version, and ask your fitter or building control if you're not sure.
- Approved Document F: Ventilation: background ventilation and trickle vents
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