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

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.

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.

Trickle vents can affect sound reduction

It's worth noting that adding trickle vents to windows can impact any noise reduction measures you have on your windows. Unfortunately, it 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. Read more about the transmission of sound through glass here.

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...

The Main Types of Trickle Vents Include:

• Through Frame or Through Sash Design
  The most common type of trickle vent used in modern window frames. The vent is fitted in to the top of the frame or into the openeing sash above the glazing unit.  This is the trickle vent we offer most frequently at Everest.
  
  
• 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.

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?

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...

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.

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.