Window trickle vents introduce fresh air into a home, aiding in temperature control and reducing condensation on window panes. It’s especially important to install these vents in modern, well-insulated homes with limited natural ventilation. By ensuring a continuous exchange of air, trickle vents help to create a healthier living environment and can also assist in meeting building regulations related to ventilation and air quality.

This article tells you everything you need to know about why trickle vents are necessary in double glazed windows and what their advantages and drawbacks are. It offers guidance on assessing the need for vented windows in your home so you can make an informed decision about them that’s tailored to your living environment.

What are window trickle vents?

Window trickle vents are small ventilation features installed in window frames. The vents are designed to allow for a continuous, controlled flow of fresh air into a home. This passive ventilation system helps maintain air quality, regulate indoor temperature and reduce the build-up of condensation and mould by allowing moist air to escape.

The UK’s Building Regulations, which were updated in 2022, require most new or replacement window installations to include trickle vents. The inclusion of vents ensures adequate ventilation in homes, especially in modern, well-sealed buildings whose natural airflow might be restricted.

Different types of trickle vents have unique mechanisms and installation methods:

Slot vents

Slot vents are integrated directly into the window frame. A small slot is cut into the frame, and a cover that can be manually adjusted is placed over the vent. Air flows through the slot, allowing for controlled ventilation.

Adjusting the vent’s opening allows the homeowner to increase or decrease the amount of air passing through it. This flexibility makes slot vents a popular choice for easily managing airflow based on weather conditions and personal preferences.

Glazed-in vents

Glazed-in vents are incorporated into the window’s glass unit, typically at its top. They provide a seamless look that doesn’t detract from the window frame’s aesthetic. Each vent consists of a hollow section within the glazing bead. Air passes through a series of channels built into the glass unit’s spacer bar.

Like slot vents, glazed-in vents can often be adjusted to control the volume of air that enters the room. Because their design makes them less noticeable than slot vents, glazed-in vents offer a discreet option for maintaining indoor air quality without compromising your windows’ appearance.

Why are trickle vents necessary?

Trickle vents are necessary for several key reasons that have led to their inclusion in Building Regulations provisions concerning new homes and installations of new and replacement windows.

The primary purpose of trickle vents is to provide continuous background ventilation. This constant air exchange is crucial in modern buildings whose natural ventilation may be limited because of advancements in construction techniques to improve energy efficiency. Without adequate ventilation, air quality inside a home can deteriorate, which can lead to various types of problems.

Trickle vents play a critical role in reducing the amount of condensation that forms when moist, warm air inside a home comes into contact with cooler surfaces such as windows. Over time, the presence of moisture can lead to the growth of mould, which not only damages building materials and window frames but also poses health risks to occupants, particularly those with respiratory problems.

By letting a controlled flow of fresh air into the home, trickle vents help to dilute and remove pollutants and odours, contributing to a healthier living environment. This is especially important in kitchens and bathrooms, where moisture and odours are more prevalent.

Updated regulations concerning the inclusion of trickle vents in replacement window installations and new home construction ensure that even as properties become more energy-efficient, they do not compromise on air quality or create conditions conducive to dampness and mould growth. These regulations underscore the importance of balancing energy efficiency with the need for healthy indoor environments.

Pros Improved air quality: trickle vents allow fresh air to circulate within the home, diluting and removing indoor pollutants and odours and thus enhancing overall air quality. Reduction in condensation and mould: by ensuring a steady flow of air, trickle vents help reduce the risk of condensation on windows and walls, which in turn minimises the likelihood of mould growth. Increase in energy efficiency: trickle vents can help maintain energy efficiency by allowing for controlled ventilation without needing to fully open the windows, which can lead to heat loss, especially during colder months.
Cons Noise pollution: in noisy environments, open trickle vents may allow external sounds to enter the home, potentially disturbing its peaceful atmosphere. Aesthetic concerns: some homeowners may find trickle vents visually unappealing or feel that they detract from the windows’ appearance, especially in traditional or historic properties.

Are trickle vents suitable for all window materials?

Trickle vents are versatile and can be installed in windows made from a wide variety of materials, including unplasticised polyvinyl chloride (uPVC), wood and aluminium. Their design allows the vents to be integrated into new windows regardless of the materials they are manufactured from, making the vents suitable for diverse architectural styles and homeowners’ preferences.

uPVC windows

uPVC window frames are a practical solution for improved home ventilation. Trickle vents are commonly found in uPVC windows because of this material’s popularity in modern construction. uPVC frames can easily accommodate trickle vents, which are slotted into them or included in the glazing units.

Wooden windows

Wooden windows can also be fitted with trickle vents. While wood is a traditional window material, modern wooden windows are designed to meet current building regulations, including those that address the need for adequate ventilation. Trickle vents can be discreetly incorporated into wooden frames, preserving their aesthetic appeal while enhancing their functionality.

Aluminium windows

Aluminium frames, which are known for their strength and slim profiles, are also compatible with trickle vents. The vents can be integrated into the aluminium frames, providing essential ventilation without compromising the windows’ slimline appearance.


Exemptions to trickle vents in windows

Listed buildings and conservation areas are usually exempt from the requirement to install trickle vents in windows in order to preserve these buildings’ and areas’ historical and architectural integrity.

Listed buildings

Any alterations that could affect listed buildings’ character and appearance may require Listed Building Consent. The installation of modern features such as trickle vents is one of these alterations. As the visual impact of trickle vents might not align with preservation goals, you may want to consider alternative ventilation strategies to maintain indoor air quality without compromising your building’s historic value.
Historic structures featuring vapour-permeable materials that absorb moisture and let it evaporate quickly can be exempt from trickle vent requirements. Examples include buildings made with wattle and daub, cob or stone and those constructed using lime render or mortar.

Conservation areas

Similar considerations apply to properties within conservation areas, where the goal is to maintain their aesthetic. While conservation area consent doesn’t always strictly prohibit modern interventions such as trickle vents, any modifications to windows must usually adhere to guidelines that preserve the area’s visual character. So installing visible trickle vents might be discouraged or subjected to specific conditions.

Alternative solutions

In situations in which trickle vents are not suitable or permitted, other ventilation methods may be employed to ensure adequate airflow, such as the use of extractor fans, mechanical ventilation systems or open windows. These alternatives aim to balance the need for modern living standards with the desire to conserve the UK’s historic and architectural heritage.

Can trickle ventilation be installed in existing windows?

Trickle ventilation can be installed in existing windows. This task is often a straightforward DIY job that involves fitting the vent into the window frame.

DIY installation

If you’re comfortable with basic DIY tasks, installing trickle vents involves creating precise openings in the window frames and fitting the vent units. 

You will need these items:

  • A through-frame trickle vent
  • A pencil for marking the vent position
  • A tape measure
  • A spirit level
  • Drill bits designed for the frame material 
  • A drill
  • Fine 240 grit sandpaper
  1. First, use a tape measure to find and mark the midpoint of the inside frame above the sealed unit and the frame’s vertical centre
  2. Next, place a spirit level on your mark to ensure accuracy. Draw a horizontal line with your pencil. Make sure your original centre mark remains clear and visible
  3. Determine the fixing centre measurement by measuring the distance from the centre of one fitting hole on the trickle vent to the centre of the other
  4. Halve this measurement and extend your tape measure accordingly. Align this midpoint with the centre line you have marked on the frame. Then, mark the starting point and endpoint of the fixing hole measurement along this line
  5. If your vent has additional clips, use the same technique to mark them
  6. Repeat these steps on the outside of the frame so that you have identical measurements
  7. Use a 2mm drill bit to make a small pilot hole at each fixing hole and any clip holes. Be sure to hold the drill horizontally and vertically level to make perfectly straight holes
  8. For uPVC windows, use a high-speed steel (HSS) drill bit, which is designed for use with metal. This type of window typically has a thin metal reinforcing strip inside its frame that’s easy to drill through
  9. For a wooden window frame, use an HSS or a specialist wood drill bit
  10. After drilling the pilot holes, verify their alignment from the other side of the frame. Then, switch to a larger drill bit corresponding to the size of the screws, clips or fixing points. Make sure each hole is drilled straight
  11. Lightly sand off any rough edges with sandpaper. Be careful not to mark the frame excessively
  12. Identify and mark approximately four evenly spaced points along the line between your fixing holes. Use the same pilot drill bit to drill through the frame. Keep the drill level when you hold it
  13. Make sure the drill bit penetrates the entire frame. Remember that most window frames are about 50mm thick. To prevent internal frame damage, avoid applying excessive force while drilling. Instead, allow the drill to work at its own pace
  14. Swap the pilot drill for a larger drill bit that’s approximately 5.5-6mm in size and re-drill all the holes to make them larger
  15. Attach the two sections of your trickle vent to the window frame. Make sure you place them on the correct side. The sections will be labelled “internal” and “external,” with the insect grill, or small mesh, always facing outward
  16. Assemble the outer and inner sections by screwing or clipping them together

For windows still under warranty, checking the terms before proceeding with DIY installations is advisable. Adding trickle vents could affect the warranty, so it’s a good idea to consult with the company that provided the warranty to ensure that adding trickle vents won’t invalidate your coverage.

How much do trickle vents cost?

Trickle vents are included in the cost of new windows, so there’s no extra charge when they’re part of a window installation. If you’re looking to retrofit trickle vents onto your existing windows, you can purchase them separately.

The cost of stand-alone trickle vents varies depending on their size, material and design, but they are generally quite affordable. Prices can range from around £15 for basic models to at least £25 for advanced designs with additional features such as enhanced noise reduction. Installing trickle vents is a cost-effective way to improve ventilation and air quality in your home without the need for major renovations.

Trickle ventilation FAQs