Aluminium Square Weather External Louvres

Square weather louvres are external wall vents that provide weatherproof ventilation for plant rooms, commercial buildings, residential walls and roof spaces. We stock cast aluminium square louvres with 45° fixed blades, a 38mm depth and a 90% free area — the highest free area available in a weatherproof louvre, letting you meet airflow requirements without oversizing the opening. Bird mesh is fitted as standard to prevent pest and insect entry, and all louvres are suitable for both supply and extract applications. Available in 10 standard sizes from 150mm to 600mm, with bespoke made-to-measure louvres available for non-standard openings. All sizes in stock with next-day delivery.

Circular Weather Louvres / Grilles & Louvres / Fire Dampers / MVHR Units

What is a square weather louvre used for?

A square weather louvre is fitted to an external wall opening to allow ventilation air in or out of a building while keeping rain, wind-driven debris and wildlife out. They are the standard external finish for any square or rectangular wall penetration that carries ventilation. Typical uses include plant room intake and exhaust, commercial kitchen extract, warehouse and industrial building ventilation, AHU louvre faces, car park ventilation and residential builder's openings. The 45° fixed blade deflects driving rain down and away from the opening while allowing air to pass through freely.

What sizes of square weather louvre do you stock?

eFans stocks 10 standard sizes from 150mm to 600mm square in 50mm increments: 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, 500mm, 550mm and 600mm. The stated size is the outer frame dimension, and the louvre fits over or into a matching wall aperture. For non-standard or rectangular openings, we offer bespoke made-to-measure louvres in any size and any RAL colour. Contact us on 0161 818 2050 or hello@efans.co.uk for a bespoke quote.

What is the free area of a square weather louvre?

Our square weather louvres have a 90% free area — meaning 90% of the face of the louvre is open to airflow, with the remaining 10% taken up by the frame, blades and bird mesh. This is the highest free area available in a weather louvre and gives a significant advantage over circular weather louvres, which typically offer only 50% free area. The higher free area means less pressure drop across the louvre, lower fan energy consumption, and less noise at the terminal. For any high-volume extract or intake application, square is the more efficient choice.

Square vs circular weather louvre — which should I use?

Square louvres give higher free area (90% vs 50%), larger sizes (up to 600mm vs 315mm), and are the standard choice for commercial plant rooms, AHUs and rectangular builder's openings. Circular weather louvres are sized to match round duct diameters and are the right choice where a single round duct terminates at the wall — typically bathroom extract, kitchen extract and MVHR terminations at 100mm to 315mm. As a rule of thumb: round duct, single terminal, domestic or light commercial = circular. Rectangular opening, plant room, AHU or high-volume = square.

Are these louvres suitable for both supply and extract?

Yes. The 45° fixed blade design and 90% free area make them suitable for both supply (intake) and extract (exhaust) applications. On supply louvres in coastal or exposed locations, consider specifying a secondary drift eliminator behind the louvre to catch any water carried through the blades during severe weather — we can source this as a made-to-order option. On extract louvres, no additional weather protection is usually required as airflow is outbound.

What is the blade angle and why does it matter?

The 45° blade angle is the industry standard for weather louvres. It deflects driving rain downward while still allowing free airflow through the face. A steeper blade angle provides better weather protection but restricts airflow and increases pressure drop. A shallower angle improves airflow but allows more rain ingress in high wind conditions. 45° is the balance point that works for the vast majority of UK weather exposures. For exposed coastal or high-wind sites, specify a dedicated storm-proof louvre with a secondary drift eliminator.

Do square weather louvres come with bird and insect mesh?

Yes. All louvres in this range include a galvanised bird mesh fitted as standard at the rear of the frame, providing protection against birds, rodents, insects and larger debris. This meets Building Regulations Part F requirements for external ventilation openings. For food production, clean room or pharmaceutical facilities that need a finer insect mesh, or for coastal sites that need stainless steel, we can specify alternative mesh to order.

Can I use a square weather louvre on a fire-rated wall?

The louvre itself does not provide a fire rating — it is an external weather finish only. If your wall opening passes through a fire compartment wall and you need to maintain fire rating under Building Regulations Part B, you must install a fire damper within the duct behind the louvre. The damper closes automatically in a fire to maintain compartmentation, while the weather louvre continues to provide the external weather seal. We stock EN 1366-2 tested fire dampers in matching sizes — contact us for specification advice.