21 October 2025
Trickle vents sound simple, but they raise a lot of questions. Are they needed? Are they required by Building Regulations? What happens if they are not used? This guide from SashWise explains what trickle vents do, how they fit into UK Building Regulations, and the main pros and cons for timber windows.
If you are installing complete new timber windows or considering upgrading your current timber windows, then you have probably come across the term tickle vent.
A trickle vent is a small opening built into the window frame or the sash that provides background ventilation. Their function is to allow air to move slowly through the property to avoid condensation, damp, and stale air.
Unlike opening the window, a trickle vent can be left open without causing a strong draught or posing a security risk.
Timber is a natural material that reacts to humidity. If moisture builds up inside a room, condensation can form on the glass and nearby timber surfaces. Over time, this can cause paint to flake and blister, and wood to decay and rot.
In June 2022, UK Building Regulations Approved Document Part F was updated with a focus on improving ventilation in houses. The aim being to ensure sufficient quality of air in living spaces and to prevent a build-up of condensation.
Whether you must incorporated trickle vents into timber windows depends on what you are doing:
New windows in a new build: The building design must comply with Part F, this normally includes permanent background ventilation. Trickle vents are the easiest and most cost effective way of achieving this.
Replacing existing windows: Any windows being replaced that have existing trickle vents, the new windows must also have vents of at least the same size. Where the windows being replaced do not have trickle vents, it must be demonstrated that ventilation will not be made worse by the new windows. If the room will be made significantly more airtight by the new windows then trickle vents will need to be incorporated in the new windows.
Refurbishment of existing windows: The same rules apply. Assuming the refurbishment of the windows does not make the room significantly more airtight then trickle vents do not need to be fitted. It is also often impractical to retro fit trcikle vents into existing window frames.
Our expert staff at SashWise will be more than happy to advise you as to whether or not trickle vents are required on your window project.
Steady Background Airflow: They provide a constant, gentle exchange of air without the need to open windows.
Easily Comply with Building Regulations: They offer a straightforward solution to comply with Part F, particularly for replacement windows.
Cost Effective: They are very low cost to install, and require no on going running or service costs compare to mechanicalextract or heat recovery systems.
Can Let In Outside Noise: Despite only being a small vent they can still allow external noise pollution to penetrate the room.
Slight Heat Loss: Any opening no matter how small can allow warm air to escape. The loss is small, but may still be noticeable if vents are left open in very windy or cold conditions.
User Error: There is a temptation to close the vents permanently to avoid any draughts, but this negates the benefit of the trickle vents. Equally if they are constantly left open, dust can build-up restricting the air-flow or ultimately blocking the vent entirely.
Aesthetic Impact: No matter how discreet, fitting a plastic vent into a timber window will have an adverse impact on the visual look of the window.
Within the vast majority of timber windows the trickle vents is fitted to the face of the window frame or the sash above the glazing. This means that the plastic vents are clearly visible both internally and externally, making them unsightly, obtrusive and significantly detracting from the aesthetics of the windows.
At SashWise we fully appreciate our clients reluctance in having to have trickle vents in their beautiful new timber windows. That is why we have devised a system to manufacture our new Accoya timber windows with concealed trickle vents. Our hidden trickle vents fully comply with the ventilation requirements of current Building regulations, whilst at the same time not detracting from the elegance of our handcrafted timber sash and casement windows.
Please complete the form to discuss your sash window requirements or for further information about our services.
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Unit 39, Railway Arches
Popes Grove
Twickenham TW1 4JW
Tel: 0208 977 4627
