Trickle Vents Available now at Duffells Locks & Security to the Trade

What are Trickle Ventilators?

Trickle ventilators, also known as trickle vents, window ventilators, or door ventilators are small ventilation systems integrated into the frames of doors and windows. They are designed to allow a constant, controlled flow of air from the outside into an internal space, which is particularly important in modern, airtight homes.

Trickle vents are composed of a staggered slit within the frame, present on both the interior and exterior sides and typically feature an adjustable cover that can be opened or closed. However, they are typically designed so the door/window can be left closed while the trickle vent is kept open at all times for continuous airflow.

Trickle Vent Airflow

The primary function of trickle vents is to provide background ventilation. This continuous airflow is crucial for maintaining indoor air quality by removing excess moisture and reducing the risk of mould buildup. 


What are the benefits of trickle vents?

Trickle Vent

Constant Air Circulation: By allowing a continuous 'trickle' of air to flow in and out of the building, these vents help to replace stale indoor air with fresh outdoor air. This continuous exchange is crucial in maintaining a healthy indoor atmosphere. By facilitating the exit of stale air and entry of fresh air, trickle vents also help in removing unpleasant odours, contributing to a more comfortable living environment.

Moisture Control: Trickle vents help in reducing excess humidity and moisture inside the home. By allowing damp, moisture-laden air to escape and be replaced by drier air from outside, they reduce the risk of mould and mildew growth, which are harmful to both the structure of the building and the health of occupants.

Reduction of Indoor Pollutants: Homes can accumulate various pollutants, such as carbon monoxide, carbon dioxide, volatile organic compounds (VOCs), and other airborne chemicals from cleaning products, cooking, and other sources. Trickle vents help dilute these pollutants by allowing fresh air to enter and contaminated air to exit.

Health Benefits: A well-ventilated space is essential for good respiratory health. Trickle vents can be particularly beneficial for individuals with respiratory conditions like asthma or allergies by ensuring a consistent supply of fresh air and reducing the concentration of allergens and irritants in the indoor air.

Noise reduction: By restricting the need to open a door or window, trickle vents will allow fresh air to circulate the room whilst minimising the level of outdoor noise allowed to enter the room.

Condensation reduction: Condensation occurs when moist air comes into contact with a colder surface, like a window, and the moisture in the air turns into water droplets. Trickle vents help regulate the humidity level inside a building by allowing moist indoor air to escape and be replaced with drier outdoor air. This exchange helps maintain a balanced moisture level, reducing the likelihood of condensation forming on windows and other surfaces.

Energy Efficiency: While mechanical ventilation systems can also reduce humidity, they often require more energy to operate. Trickle vents provide a passive, energy-efficient solution, requiring no additional energy to operate and still effectively managing indoor humidity and condensation levels.


Are Trickle Vents mandatory?

As of June 2022, all new and replacement windows need to have a trickle vent, particularly in new builds and when replacing windows or doors. This requirement is part of the UK Building Regulations, specifically under Part F which deals with ventilation. The regulations aim to ensure adequate air circulation and ventilation in homes to maintain good indoor air quality, especially as modern construction methods have made buildings more airtight.

Key points regarding the requirement of trickle vents in the UK include:

New Builds and Renovations: For new buildings and when existing windows or doors are replaced in older buildings, the installation of trickle vents is typically required to meet the ventilation standards set out in the regulations.

Compliance with Standards: The specific size and capacity of the trickle vents should comply with the standards outlined in the regulations to ensure they provide sufficient airflow. Further details on size and capacity are explained later in this article.


They are particularly beneficial in regulating temperature and humidity levels inside the home and are essential in reducing condensation.

Trickle vents are often a requirement in most new and replacement windows under Building Regulations, reflecting their importance in modern building design.


Can trickle vents be fitted to existing windows?

Yes, trickle vents can be fitted to existing windows. This is a common practice, especially in situations where improving ventilation in older buildings is necessary to meet modern building standards or to address issues like condensation and poor air quality.

Here are some considerations before installing…

Window Material: The ease of installation can vary depending on the material of the window frame (uPVC, wood, aluminium, etc.). Some materials are easier to work with than others.

Structural Integrity: Ensure that adding vents won't compromise the structural integrity of the window. Avoid drilling near glass or in areas that might weaken the frame.

Compliance with Regulations: Check building regulations to ensure compliance, especially regarding the size and placement of the vents.


What are the Building Regulations for Trickle Vents?

In June 2022, the Building Regulations Approved Document Part F underwent a revision with an emphasis on enhancing ventilation in homes, particularly as buildings are being constructed to be more airtight.

The updated regulations highlight the importance of background ventilation, which works in conjunction with other ventilation strategies to maintain air quality in living spaces and to prevent condensation accumulation.

Under these revised guidelines, if windows being replaced already have background ventilators (such as trickle vents), the new windows must also be equipped with ventilators of at least the same dimensions.

For replacements of existing windows that lack trickle vents, it must be ensured that the ventilation efficiency is not reduced by the new windows. Given that many modern windows are designed to be more airtight than their older counterparts, the inclusion of trickle vents in new window frames is generally necessary.

It’s important to be aware that windows designed to lock while allowing a ventilation gap, are not considered an adequate alternative to trickle vents for the purpose of background ventilation as per the Building Regulations.

For more detailed information, you can refer to the new rules for Building Regulations Part F at the following link: New rules for Building Regulations Part F.


What are the key attributes when choosing your Trickle Vent?


This refers to the horizontal measurement of the vent opening. It's the longer dimension that stretches across the width of the vent. The length of the slot is crucial because it determines the overall area of the opening through which air can pass. A longer slot length typically allows for a greater volume of air to flow through the vent, contributing to more effective ventilation.


This is the vertical measurement of the vent opening, essentially the thickness or the narrower dimension of the slot. The height of the slot plays a significant role in regulating the rate of airflow. While a taller slot height can allow more air to pass through.


This is the metric that indicates the efficiency of a ventilator's aerodynamics. This is represented by the size of an equivalent sharp-edged circular orifice that would allow the same amount of air to flow through it as the ventilator in question, given the same pressure difference applied.

The equivalent area for a background ventilator is calculated based on a 1Pa pressure difference, requirements are outlined in the provided table:


Room Minimum equivalent area of background ventilators for dwellings with multiple floors Minimum equivalent area of background ventilators for single-storey dwellings
Habitable rooms 8000mm² 10,000mm²
Kitchen 8000mm² 10,000mm²
Utility Room No minimum No minimum
Bathroom 4000mm² 4000mm²
Sanitary Accommodation No minimum No minimum


The use of this table is not appropriate for all situations and the Building Regulations Document Part F must be referred to for further details.


This value refers to the volume of air in m² that can flow per hour through each square metre of the building envelope at a pressure differential of 50 pascals.

In the UK, the level of airtightness is measured as air permeability in the unit m³/h. m² at 50Pa (q50).


This measurement indicates the maximum water pressure a trickle ventilator can withstand in its closed position without allowing any water to leak through. The water tightness of trickle  ventilators is assessed under the standard BS EN 13141-1:2019.


Airborne sound insulation, measured in decibels (dB) for trickle vents, is an important aspect to consider, particularly in noisy environments. This term refers to the ability of the trickle vent (or any building element) to reduce the level of sound that passes through it from the outside to the inside of a building. Here's a breakdown of this concept:

  1. Decibels (dB): Decibels are the units used to measure sound intensity. The scale is logarithmic, meaning that a small increase in dB represents a significant increase in sound intensity. In the context of building elements like trickle vents, the dB rating indicates how effective the vent is at reducing the volume of incoming noise.
  2. Airborne Sound: This refers to sound that is transmitted through the air, such as traffic noise, voices, music, etc. This is different from impact sound, which is sound generated by an object hitting another object (like footsteps on a floor).
  3. Sound Insulation of Trickle Vents: Trickle vents are designed to allow air to pass through while minimizing the passage of sound. The sound insulation capacity of a trickle vent is often quantified in dB. A higher dB rating means the vent is more effective at blocking sound. For example, a trickle vent with a rating of 30 dB will reduce the incoming noise level by 30 decibels.
  4. Specialised Trickle Vents for Noise Reduction: In areas with high noise levels, specialised trickle vents with enhanced sound insulation properties are used. These vents have additional features like thicker or multiple layers of sound-absorbing materials, designed to reduce the transmission of airborne sound more effectively than standard vents.
  5. Regulations and Standards: Building regulations in some regions may specify minimum sound insulation requirements for trickle vents, especially in residential buildings near airports, busy roads, or industrial areas. These regulations ensure that the indoor environment remains relatively quiet and comfortable for the occupants.


In summary, trickle ventilators, commonly known as trickle vents, are essential components in modern building design, particularly in airtight homes. They play a critical role in maintaining indoor air quality by facilitating constant air circulation, regulating moisture and humidity, reducing indoor pollutants, and providing health benefits, especially for those with respiratory conditions. These vents also contribute to noise reduction and energy efficiency.

The necessity of trickle vents in new and replacement windows is underscored by UK Building Regulations, particularly Part F, which was updated in June 2022 to enhance home ventilation. These regulations mandate the installation of trickle vents in various circumstances, taking into account the property's age, type, and existing ventilation systems. Trickle vents are generally required unless a property is exempt, such as in the case of listed and historic buildings, or where alternative ventilation strategies are in place. You should always check with Building Control or other appropriate authorities to determine whether your ventilation solution is suitable, do not rely on the general information provided in this blog.

For existing windows, the addition of trickle vents is a common practice, especially necessary for older buildings needing to meet modern ventilation standards. The process requires careful consideration of the window material, structural integrity, and compliance with regulations.

When selecting trickle vents, key attributes like slot length, slot height, equivalent area, air permeability, watertightness pressure, and airborne sound insulation must be considered. These attributes determine the vent's effectiveness in air exchange, resistance to weather elements, and noise reduction capabilities.

Ultimately, understanding and adhering to these regulations and considerations is crucial for ensuring that buildings not only comply with legal standards but also provide safe, comfortable, and healthy living environments. Whether for new constructions or replacements, the incorporation of trickle vents plays a vital role in modern architectural practices.


This blog is intended as a guide to the operation of the products in it. Whilst we may describe standards and scenarios, we cannot recommend the use of these products for a specific environment or circumstance. The specification of any product must be undertaken by the professional on-site who has knowledge of the building, its inhabitants, its intended use, and any other requirements. We cannot say that a product is suitable for a specific use case.