If you have stood in a downpour looking up at the little grille set into your wall and wondered whether it is about to let the weather in, you are not alone. Louvre vents get asked about more than almost any other small building product, and most questions come down to a handful of concerns: will it leak, will it let mice in, why is it even there, and will it fix a damp problem. Below we work through these, with honest answers rather than sales talk.
What is a louvre vent?
A louvre vent is a ventilation cover made up of angled slats, usually set between 30 and 45 degrees, fitted into an opening in a wall, door, or duct run. Air passes freely through the gaps in both directions, but the angle physically stops most wind driven rain and larger debris being pushed straight through. Behind the slats there is normally a flyscreen mesh too, stopping flies and larger insects from using the opening as a way in or out.
You will see them called a few names depending on where they are used, including louvre vent covers, plaster vent covers, and internal vent covers, but they all do the same job. They come in plastic, usually white or brown, or aluminium for a more durable, paintable option, in sizes from a small internal duct cover to a full sub floor airbrick. The louvre vent collection covers the common sizes and finishes.
Do louvre vents leak?
This is probably the most common louvre vent question, and it deserves a straight answer: a correctly fitted louvre vent should not let rain through under normal weather. The slat angle is not decorative, it is designed to shed water off the outside face rather than channel it inward, the same way rain runs off angled roof tiles.
So why do people find damp patches near a vent and blame the vent itself? In the vast majority of cases, water getting in is not a fault with a properly made vent. It is almost always down to the surrounding mortar joint or sealant failing over time, letting water track in around the edges, or the vent having been fitted with slats facing the wrong way, turning the water shedding design into a water collecting one. Both are fitting and maintenance issues, not a flaw in the product. If you suspect a leak, check the pointing and sealant around the frame first, and confirm the slats slope downward and outward.
Will a louvre vent keep out mice?
No, and this is worth being upfront about. Standard louvre slats, and the flyscreen mesh fitted to most louvre vents fixed or removable, are sized to stop flies and larger flying insects, not rodents. That mesh is nowhere near fine enough to stop a mouse, which can squeeze through gaps of just a few millimetres.
If rodent access is a genuine concern, a standard louvre vent alone will not do the job. What is needed is a dedicated fine rodent mesh fitted behind or in place of the standard flyscreen, with a small enough aperture to block rodents while still allowing airflow through. It is a genuinely different product, not just a finer screen, so check specifically for rodent mesh. Vents are also only one entry point, gaps around pipework and damaged airbricks are common routes in too, so a mouse problem needs looking at the whole building.
Why is there a louvre vent on my wall?
If you notice a small grille low down on an exterior wall, it is almost certainly a ventilation vent rather than anything decorative. Most commonly, a louvre vent set low in an external wall supplies background ventilation to the sub floor void beneath a suspended timber floor. Many UK houses have a gap under the ground floor, with floorboards sitting on joists above bare ground, and that space needs a constant supply of fresh air. Without it, moisture builds up over time, leading to condensation, mould, and eventually timber rot if left unaddressed, all happening slowly out of sight, which is why background ventilation is required from the start.
A vent is not always about the sub floor though, the same style also ventilates a room, cupboard, or duct run. Position is usually the best clue: low down near the base of an external wall, in line with the floor level, almost always points to sub floor ventilation. Options like the Securit white plastic louvre vent 9 x 6 inch or the Securit brown plastic louvre vent 9 x 9 inch cover the sizes commonly used, with a fixed flyscreen as standard.
Will using louvre vents in a shed stop damp?
Sheds are a common place people ask about louvre vents, usually after opening the door to a musty smell or mould on the walls. Adding louvre vents gives an enclosed space constant background airflow, and that genuinely helps. Sheds trap warm, moist air from garden equipment and day and night temperature swings, and with no air movement that moisture condenses on cold surfaces, creating the damp, musty conditions people mean when they ask would louvre vent stop mold in shed. Ventilation breaks that cycle by replacing trapped moist air with fresh air from outside.
Here is the honest caveat: if a shed has a more serious ongoing damp problem, ventilation alone will not fix it. Rising damp, a leaking roof, or ground level sitting above the base of the walls so rainwater pools against the timber, are structural problems ventilation cannot solve alone, those causes need addressing directly. Most shed damp is a mix of both, so fitting vents is a sensible first step, not a guaranteed complete fix.
How do louvre vents actually work?
The mechanics are simple, which is part of why louvre vents have lasted so long. The angled slats let air move freely through the gaps in both directions, giving constant, passive ventilation with no moving parts, while that same angle physically blocks rain and larger wind blown debris, directing anything that hits the slats off and away rather than through the gap. Behind the slats, the flyscreen mesh adds a second layer, stopping flying insects while still letting air pass through, and it may be fixed permanently or removable for cleaning depending on the vent.
One term worth understanding is free air space, sometimes called free area. This is the actual open area through the slats that air can pass through, always smaller than the vent's overall outer size, since the slats and frame take up some of that space. It is measured in square millimetres, and it is this figure that matters for UK building regulations, not the vent's outer dimensions. Approved Document C requires a minimum of 1500 sq mm of free air space per metre run of wall, or 500 sq mm per square metre of underfloor area, whichever is greater, with vents on at least two opposite sides for cross ventilation.
Can louvre vents be painted?
Plastic louvre vents generally should not be painted. Paint can clog the fine mesh of the flyscreen behind the slats, and once blocked the airflow through the vent is reduced, working against the whole purpose of fitting it. Paint on plastic also tends to flake over time as the plastic flexes with temperature changes.
If a colour change is genuinely needed, the better approach is usually to buy the vent in the correct colour from the outset. White and brown are the two standard colours most louvre vent covers, plaster vent covers, and internal vent covers come in. Where a colour outside those options is essential, fitting an aluminium vent instead and using a suitable metal primer and paint is more realistic, since metal tolerates a paint finish far better and will not clog a flyscreen if the mesh is masked off first.
Louvre vent questions, quickly recapped
Do louvre vents leak: no, not when correctly fitted, leaks are almost always a mortar or sealant issue, not a fault with the slats. Will a louvre vent keep out mice: no, standard flyscreens stop flies, not rodents, a dedicated rodent mesh is needed for that. Why is there a louvre vent on my wall: most often it ventilates a sub floor void, or simply a room, cupboard, or duct. Will using louvre vents in a shed stop damp: it helps with condensation, but will not fix a structural damp problem alone. How do louvre vents work: angled slats allow constant airflow while blocking rain and debris, with a flyscreen adding insect protection.
If you are ready to fit or replace a vent, the range includes the Securit aluminium louvre vent 9 x 6 inch for a durable, paintable finish, the Securit white plastic louvre vent 9 x 3 inch with removable flyscreen for easier cleaning, and the smaller Securit white plastic louvre vent 6 x 3 inch for tighter openings, alongside the rest of the sizes in the louvre vent collection.
