Should I keep trickle vents and air bricks open?

The short answer to whether they should be open is yes. Guidance for homes is explicit that air bricks, extractor fans and vents should not be blocked³, and that draught-proofing should never extend to boiler flues, air bricks or window trickle vents⁴. Trickle vents are designed to keep working even at night and while a household is away on holiday⁵.

What follows is what each opening does, when a household might reasonably reduce airflow, and what the building regulations require of replacement windows and new openings.

What trickle vents and air bricks actually do

Trickle vents provide effective background ventilation for a home, contributing to a healthy living environment by enabling unobtrusive and controllable whole-room ventilation⁵. They allow constant ventilation while a window is closed or locked, and their installation footprint does not enable intrusion into a property⁵. That combination, airflow without an open window, is the whole point of the device.

Air bricks serve the sub-floor. They help ventilate the void under suspended floors and work particularly well if placed on opposite walls, so air can cross beneath the building². Independent guidance lists air bricks in outside walls, air vents through internal walls or sealed chimneys, roof ventilation tiles or ventilated soffits, and window vents on window frames among the ventilation measures available to a home⁷.

The two are not interchangeable. Trickle vents sit at window level and serve the room; air bricks sit at the base of the wall and serve the floor structure. Both are classed as intentional ventilation, which is why guidance for homes warns against blocking air bricks, extractor fans and vents³.

Should trickle vents be open or closed? The short answer

Open, as the default. Trickle vents exist to provide background ventilation, and the guidance that accompanies them treats continuous operation as normal: even at night and while you are away on holiday, trickle ventilators can still operate to provide background ventilation⁵. The Northern Ireland Energy Agency's condensation guidance puts a daily figure on the habit, advising households to open window trickle vents during the day or when going out, or open windows for at least 10 minutes every day⁶.

The reason is moisture. Fitting windows with suitable trickle ventilation may improve a condensation problem, and could potentially reduce consequent mould growth and internal surface damage⁵. A way of reducing the risk of condensation is to ensure each room has adequate ventilation, such as trickle ventilators or other forms of ventilation⁸.

There is a limit worth stating plainly. Background ventilation provided by built-in features like trickle vents on windows or air bricks in walls is not, on its own, sufficient ventilation². Trickle vents are the baseline layer, not the whole system.

When closing them makes sense: noise, draughts and cold rooms

There are real reasons a household reaches for the shutter. Trickle vents provide ventilation without the need to open windows, reducing noise levels as a consequence, and acoustic options are also available in noisier locations⁵. A vent that is part closed still admits some air while cutting the noise path, which is why the adjustable shutter exists at all.

On draughts, the evidence points elsewhere. Thick or thermal lined curtains will help to keep draughts at bay, particularly if you only have single glazing, though curtains should be open during the day to let in sunshine and warmth⁹. For internal doors, draught excluders are described as a temporary measure only¹⁰. Neither addresses the vent slot itself.

The rooms where airflow matters most are the wet ones. Rooms where steam will be produced, such as kitchens, bathrooms and utility rooms, should be provided with higher levels of ventilation, normally mechanical fans and windows, than other rooms where suitably sized window openings and background trickle ventilators may suffice¹¹. In Wales the same distinction is drawn: other rooms may be served by suitably sized window openings and background trickle ventilators¹².

Air bricks: keep them clear, keep them open

Air bricks are the one opening in this article with no reasonable closed position. Guidance for homes states that air bricks, extractor fans and vents should not be blocked³, and draught-proofing advice repeats the point: never block boiler flues, air bricks, or window trickle vents⁴.

The consequence of blocking one is damp in a place that is hard to inspect. A blocked air brick stops the cross-flow beneath a suspended floor, so moisture that would otherwise be carried away stays in the void. The same principle applies to vents generally: it is important vents are kept clear and that the flow of air is not restricted by dust and fluff¹³.

Where an air brick supplies combustion air, the stakes rise. Air vents provided to meet Part J should not be considered as existing ventilation for a Part F room with an open-flued appliance¹⁴. Ventilation fans might cause combustion gases to spill from open-flued appliances even if the appliance and fan are in different rooms, and combustion appliances must operate safely whether or not fans are running¹⁵. Where a manufacturer's installation instructions require greater areas of permanently open air vents than the regulations specify for solid fuel appliances, the manufacturer's advice should be followed¹⁶. Permanently open air vents should be non-adjustable¹⁷.

How vents interact with ventilation rules and EPC reform

The regulatory picture has tightened. The changes to Approved Document F require the majority of replacement windows and doors to be fitted with trickle vents¹. Any new openings will have to comply with building regulations, which may impact thermal heat loss, structure, ventilation and fire safety¹⁸.

Roof and conversion work carries its own ventilation conditions. A flat roof will need to be ventilated¹⁹, and ventilation of the existing roof void will have to be considered as air must still be allowed to flow from one to another²⁰. For pitched roofs, the roof should have vents installed along the eaves to both front and rear or from side to side²¹, and where insulation is placed between the rafters, vents should also be placed along the ridge²². In Scotland, care must be taken to ensure that reliable ventilation pathways are created on the cold side of the insulated sections, with openings at both ends²³. In all circumstances, windows and rooflights should retain their full capacity to ventilate rooms²³.

On the wider policy direction, the EPC framework has been the subject of reform proposals that would bring indoor air quality into the rating. BEAMA published a position paper in November 2024 arguing that the EPC framework should incorporate an indoor air quality checklist at sale or rental transactions, linking this to the Warm Homes Plan and minimum energy efficiency standards. That is a proposal, not a rule in force.

Signs your home is not getting enough airflow

The warning signs cluster around moisture and combustion. Guidance for Wales is blunt: do not cover up holes that are supposed to be there, such as trickle vents in window frames²⁵. Independent guidance adds that households should not block intentional ventilation such as air bricks, extractor fans and vents³.

Good ventilation is achieved through a variety of methods such as trickle vents in windows, door undercuts and extractor fans²⁶. Where those routes are closed off, the symptoms tend to be condensation on cold surfaces, mould at corners and window reveals, and a stuffy atmosphere in bedrooms that have been shut up overnight.

Combustion appliances give a sharper signal. Excessive airflow can result from leaving the stove door open, improper air vent usage, or deteriorated rope seals²⁷, which is the opposite problem, but it shows how sensitive a solid fuel appliance is to the air supply around it. Where a vent has been sealed to stop a draught, the appliance may be starved instead.

For households in flats, where ventilation routes are shared and harder to alter, the constraints differ from a house. Ventilation in flats and apartments sets out how background and mechanical ventilation are handled in those buildings, and damp and mould in rented homes covers what a tenant can ask a landlord to do when airflow problems persist.