Trickle vents and Part F
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 — typical guidance is 8000mm² for habitable rooms and 4000mm² for wet rooms in naturally-ventilated homes.
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
- 2000EA vent — 300mm slot, one per opening sash, suitable for wet rooms and smaller equivalent-area requirements
- 4000EA vent — 400mm slot for larger equivalent areas; two openers with a 4000EA each cover a typical habitable room's 8000mm²
- 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.
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: typically 8000mm² per habitable room and 4000mm² for wet rooms. 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 fit has a closable flap — though Part F intends them to stay open in normal use to keep background air moving.