New Trickle Vent Legislation Set To Come Into Force

Trickle vents, a small slot in a window that can be manually opened or closed to allow for ventilation, have been required in some settings for quite a while. But now new building regulations have been approved and Document F, dealing with background ventilation, is about to come into force. This means trickle vents will be a legal requirement for the majority of window installations in England.

A house with white windows

Homeowners will have very little choice in whether they have trickle vents included in their new window designs. And their installation company, as the “competent person”, have an obligation to ensure compliance with the new building regulations and include trickle vents in their installations. Building Control and FENSA will be ensuring everyone is working to the letter of the law and it is very clear that consumers will not be able to sign waivers or use indemnity policies to avoid the use of trickle vents.

Why do your windows need trickle vents?

It may seem at odds to be adding trickle vents to your new, thermally efficient double-glazing products, especially as many people upgrade their windows and doors to eliminate draughts and heat loss. However, these new regulations are all about ensuring healthier living environments, where ventilation and air flow play an important role. Occupants need a supply of fresh air, with ventilation required to disperse moisture, odours and the indoor pollutants caused by cooking, cleaning products and the like.

Excess moisture in the air, without suitable ventilation, can contribute to mould growth and some homes can experience problems with damp after new windows and doors are installed. The gaps and cracks that have been providing ventilation in older homes are often sealed up when home improvements take place, meaning the property is less able to breathe now the only source of ventilation has been sealed.

The new legislation clearly lays out how much ventilation any habitable room requires, an “equivalent area” (EA) measured in millimetres squared. The size of the trickle vent will decide the equivalent area it provides in ventilation terms and helpfully, the amount of ventilation any new vent provides will be printed on the unit in future. It will be down to the installation company to work out how many vents are required depending on the type of room and the ventilation already in place. For example, a host room that will have no openable windows once an extension or conservatory has been added will need 10,000 mm sq EA for ventilation, whilst an existing bathroom will require 4,000 mm sq EA.

Windows in hallways and landings are exempt as not habitable rooms, but there are few other exemptions for the average homeowner. Extractor fans and air bricks are not considered as suitable alternatives for background ventilation under the new rules and leaving the windows on a lockable night vent has also been discounted due to the security issues of leaving windows ajar. If a “wet” room (in this scenario the definition of a wet room is a kitchen, utility or bathroom that houses a water source) has continuous mechanical extract ventilation, not simply an extractor fan, then no background ventilation is needed. Habitable rooms will still require 4,000 mm sq EA even with continuous mechanical extract ventilation (a system that cannot be switched off). The very small percentage of homes in England that have mechanical ventilation with heat recovery will not require trickle vents.

During your initial conversations the installation company will show you window designs illustrating the trickle vents they have included for. Following installation your fitter should show you how the new vents work and leave them in the open position. Once installed your trickle vents should predominantly be left open, however they can be manually closed for a short time as required. For example, a hay fever sufferer may want to close vents when the pollen count is particularly high but will need to open the vents again as soon as possible.

To discuss the background ventilation you will require for your replacement windows with one of our experts get in touch.


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