Louvers

The inlet half of the system

Louvers are angled blade panels fitted into walls and gable ends. They let air pass while keeping direct rain out, and they are how replacement air gets into a building at low level.

This is the part most often left out. Ridge ventilators and turbo units extract air, but air leaving has to be replaced by air entering. In a building with no low level inlets the extraction stalls, the units spin without moving much, and the conclusion drawn is that the ventilators do not work. The ventilators are fine; the building cannot breathe in.

Blade geometry

The blade angle and spacing decide the trade-off between free area and rain exclusion. Shallow blades pass more air but admit more driving rain; steeper blades exclude rain better but restrict flow.

Free area is the number that matters for ventilation calculations, and it is always less than the opening size, because the blades themselves occupy part of it. Sizing an opening by its overall dimensions rather than its free area is a common way to end up under-ventilated.

Where they go

Low on the walls, because that is where cool replacement air should enter, and distributed around the building rather than concentrated on one elevation. Inlets on only one side give a cross-draught on that side and dead air everywhere else.

Gable end louvers work with a ridge vent to move air along the length of a building. Wall louvers along the sides work with turbo units above them.

Materials

Metal louvers are the standard. Colour coated louvers are made to match the cladding, which matters on a visible elevation where a bare metal panel in a coloured wall is conspicuous.

Polycarbonate louvers pass daylight as well as air, which is useful where the opening would otherwise create a dark patch in the wall. Window louvers and ventilation windows are the same product in a smaller size for offices and welfare areas.

Insects, birds and security

A permanent opening in a wall wants mesh behind it in most industrial buildings, and food and pharmaceutical work will require it. Mesh reduces free area, so it should be allowed for at the sizing stage rather than added afterwards and quietly cutting the ventilation you calculated.

What to send us for a quote

The opening sizes, how many and on which elevations, the material and colour if it needs to match cladding, and whether mesh is required. Tell us what extraction is fitted above, because inlets should be sized against it.