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Trickle Vents


Trickle Vents: What Are They & Do You Need Them?

What are trickle vents and why do you need them in window frames? In this guide we cover the benefits of trickle vents, Building Regulation requirements and answer your common questions, such as can trickle vents be retrofitted and how many vents do I need per window?

Window Trickle Vents

What Are Window Trickle Vents?

Trickle vents are background ventilators integrated into window frames and door frames to allow a 'trickle-feed' of constant airflow from the outside to an internal space.


The trickle vent is essentially a slit in the frame, staggered on the inside and outside, with a cover that can be opened and closed. Although the vent can be closed, they are designed to be left open all the time for continual ventilation.


Trickle vents are especially important in modern houses as homes are designed to be more airtight. A constant trickle feed of air helps to remove excess moisture buildup from the air that can cause mould.


Background ventilators are required on most replacement and new windows under Building Regulations.


What is a trickle vent?

What is a trickle vent?



Everest trickle vents are designed to be effective at sound reduction.


Adding trickle vents to windows has always been a trade-off between ventilation and noise reduction. Sound is much more difficult to contain than light because a soundwave has a longer oscillation than a light wave and can diffract around corners to find its way through any small gaps such as trickle vents.


Our new trickle vent is better designed to reduce any sound leakage for better noise reduction in your window.


Everest trickle vents have been acoustically tested and proven to deliver improvement in performance compared to our previous vent.


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Everest windows have ultra-low U-values.

Trickle Vents and Building Regulations 2022

The Building Regulations Approved Document Part F was updated in June 2022. The focus was to improve ventilation in houses as buildings become more airtight.


Background ventilation is used in combination with other ventilation strategies to ensure sufficient quality of air in living spaces and to prevent a build-up of condensation.


When replacing windows that have existing background ventilators (trickle vents), the new window must also have vents of at least the same size.


For existing windows that don’t have trickle vents, it must be demonstrated that ventilation will not be made worse by the new replacement windows. As many new windows are more airtight than older windows, in most cases, trickle vents will have to be included in the new replacement window frame.


You should note, windows that have the ability to lock with a ventilation gap – known as a night latch – are not accepted as a sufficient means of background ventilation instead of trickle vents (under Building regulations).


Read more: New rules for Building Regulations Part F.


Condensation and mould on a window


What Are the Benefits of Trickle Vents?

Apart from Building Regulations requirements, why else should you consider trickle vents and what benefit do they have?

  • Ventilation
    The main benefit of a trickle vent is the ventilation that allows a potentially sealed room to have a natural flow of air to help reduce moisture in the air. Read more about ventilation here.
  • Air quality and Health
    A background trickle vent will help to reduce airborne toxins and the significant health issues they can cause. Mould loves to grow in damp and cold locations, so any excess moisture in your home increases the risk of this toxic health risk.
  • Security
    Another big benefit is the secure ability to ventilate a room without having to leave the window open.
    Some windows do have a night latch and can be securely left open with a small gap. But it’s worth noting that a night latch is not an acceptable ventilation option for building regulations (see above).
  • Energy efficient
    Trickle vents are the perfect balance of ventilation for health and help support energy efficiency.
    As homes get more airtight with insulation, trickle vents are actually even more critical to maintain air quality ensuring a constant flow of fresh air.

    A misconception is that trickle vents are bad for energy efficiency, but they can be closed and controlled in Winter if other forms of ventilation are being used.

Ventilating a room


Why Do We Need Ventilation?

Ventilation in buildings is critical to maintaining healthy living spaces. As windows and doors are considerably more draught-proof, and buildings become more energy efficient, natural ventilation from outside fresh air is reduced.


In normal living conditions and day-to-day activities, moisture is created in the air. From showering, laundry, cooking and breathing a considerable amount of water can be produced on a daily basis. This moisture becomes trapped in the home and will start to form condensation on cold surfaces. Mould then starts to grow, which is significantly dangerous to health.


Allowing air to circulate from the outside to inside a building displaces moisture from the internal air.


There are different solutions for ventilation such as mechanical exchange units, but trickle vent background ventilators in windows and doors are the most common and simplest.


Read more: Why ventilation is important in your home...


Trickle vents inside


The Main Types of Trickle Vents Include:

  • Through Frame Design
    The most common type of trickle vent used in modern window frames. The vent is fitted in the top of the frame and integrated with a staggered design to limit through draughts.

    At Everest, our trickle vents are integrated into the frame using an ‘Up and Over’ design.
  • Over Frame Design
    If a vent cannot be fitted through a frame, it can be fitted over the top of the window frame.
  • Glazed In
    The least favourable type of background trickle vent because it detracts so much from the aesthetic of the window. The vent is fitted into the glazed area between the sealed glass unit and the frame profile.

    At Everest, we don’t use Glazed In or Through frame trickle vents.

Can You Fit Trickle Vents to Existing Windows?

A trickle vent can be installed in existing windows, but for best results, we don’t recommend this at Everest.


Retrofitting a trickle vent is done by drilling through the existing frame. It’s not an easy job and if your measurements are not perfect then your frame will have big holes that you can’t fill!


To get the most efficient background ventilation in a window frame, the design of the trickle vent needs to be built into the window frame profile.


Do I Need Trickle Vents?


Do I need trickle vents? flow chart diagram

Do I need trickle vents? flow chart diagram


Building Regulation requirements for trickle vents are different depending on the age and type of property you have:


  • Homes using mechanical ventilation and heat recovery are designed to be airtight and ventilation is provided mechanically. Trickle vents are not needed.
  • Homes using continuous extract ventilation systems use a combination of mechanical and natural ventilation. Trickle vents must be installed.
  • Existing properties without trickle vents when replacing windows must demonstrate that the new windows do not increase airtightness (unlikely). Or, the new windows must have trickle vents.
  • Existing properties with trickle vents can replace the windows with at least the same size trickle vents, or more (but not less).

Most replacement windows will require trickle vents to be installed unless there is an exemption (see below), or the property can demonstrate sufficient levels of other background ventilation.


Read more: Size requirements and how many trickle vents are needed in windows...


Exceptions to Trickle Vent Installation

A house using mechanical ventilation with heat recovery should not install trickle vents under Building Regulations. Note that continuous mechanical extract ventilation does require the use of background ventilation.


Listed and historic buildings are exempt from the installation of trickle vents:

  • Those listed in accordance with section 1 of the Planning (Listed Buildings and Conservation Areas) Act 1990.
  • Those in a conservation area designated in accordance with section 69 of the Planning (Listed Buildings and Conservation Areas) Act 1990.
  • Other historic buildings with a vapour-permeable construction that both absorbs moisture and readily allows moisture to evaporate. These include those built with wattle and daub, cob or stone and constructions using lime render or mortar.

Other exceptions to note are for houses adjacent to busy roads and susceptible to pollution. In those cases the size of trickle vents should be as high as possible and located on the less polluted side of the building. It is suggested that mechanical ventilation might be the better option.


What Choice Do Homeowners Have about Trickle Vents?

Some homeowners prefer a window frame without trickle vents. The most common reasons are:

  • Aesthetic – window frames look better with clean profiles
  • Dirt trap – the vents can be difficult to clean
  • Noise – the gap in the frame can cause some noise to leak from outside
  • Draughts – open vents can cause cold spots

Window frames do look better without a trickle vent, but the benefits of using trickle vents as part of a ventilation system in the whole house cannot be ignored.


Trickle vent design today is far better than early ventilator designs and modern trickle vents are seamless with the frame. Everest trickle vents have insect screens to stop tiny insects to keep bugs out and have an easy-to-clean design.


What cannot be avoided is that in many circumstances, the installation of new windows will require trickle vents to be fitted so that the window passes Building Regulations. At Everest, we cannot supply windows without vents where they are required.


If a homeowner was to fit windows without trickle vents when they are required, they might have an issue when trying to sell the house without full Building Regulations.


When buying new windows, make sure that you take advice from a registered supplier who can help you comply with regulations.


At Everest, we can advise you on what you need to ensure that all regulations are followed. We will provide you with a certificate that shows the work was completed by a registered supplier and that the windows meet Building Regulations.


The information above is provided as a guide only and correct at the time of publication: March 2023.


We recommend you read in full Building Regulations Approved Document Part F.


Building Regulations are subject to change. Always seek approval from your local planning authority before starting any building work.


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Commonly Asked Questions

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    Do trickle vents stop condensation and damp?

    Trickle vents provide background ventilation that contributes to reducing moisture in the air which causes condensation and mould.


    If a house produces excessive moisture then additional ventilation may be necessary to stop condensation.


    Read more: How to stop condensation on windows...

  • +
    Should trickle vents be open all the time?

    Technically, a trickle vent can be manually opened or closed.


    However, trickle vents are designed to provide a constant background feed of air to reduce moisture and improve air quality. Building regulations state: "Background ventilators are intended to normally be left open."


    In Winter, it might be necessary to close the trickle vent in cold weather. But it’s advisable to 'air' and ventilate the room every day to avoid a build-up of toxins and moisture.

  • +
    Can I get trickle vents for wooden windows?

    Trickle vents can be fitted in all types of window frames, including wooden windows.


    Vents are integrated into the frame during manufacturing. Retrofitting vents to an existing frame may not be possible for wooden windows and can be tricky for uPVC.


    At Everest, we do not retrofit trickle vents to windows.

  • +
    Should all windows have trickle vents?

    Trickle vents are required by Building Regulations when replacing windows that already have trickle vents fitted. For new window frames that are replacing old windows without vents, it must be demonstrated that ventilation will not be made worse by the installation of the new energy-efficient window.


    In most cases, trickle vents are required to be fitted in new windows.

  • +
    Where should trickle vents be fitted?

    Trickle vents should be fitted at a minimum of 1.7m from the floor to avoid draughts. Vents are integrated into the head of the window frame.

At Everest, Energy Efficiency Is at the Core of What We Do

When you choose Everest, not only do you make your home warmer and reduce your energy bills, but you also reduce your CO₂ emissions by consuming less energy to heat your home. We ensure an environmentally friendly manufacturing process and recycle all old products.


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