Wind Loads & Aluminium Windows

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Getting wind loads on aluminium windows right is why a window that suits one project can be wrong for another.

Why do wind loads matter for aluminium windows?
Wind pushes and pulls on a building’s facade, and windows and doors must resist that pressure without excessive deflection or failure. Because the load depends on the building’s height, location and exposure, the same window cannot be used everywhere — larger or more exposed openings need stronger glass, frames and mullions, confirmed by design.
Please note: This guide explains wind-load principles in general terms. It does not publish design pressure values. Wind loads and the resulting glass, frame, mullion and transom requirements must be determined for the specific building and site by reference to the applicable standards, an approved design or a competent person.

Wind is the invisible load that shapes how aluminium windows and doors are specified. It is also the reason a window that is perfect for one project can be wrong for another. This guide explains wind loads and aluminium windows in plain terms — the principles, not the numbers, since the actual design pressures must be worked out for each building.

What wind loading is

When wind hits a building it creates pressure on the windward face and suction on other faces and around edges. A window or door has to carry that wind load — resisting it without bending too far, leaking, or failing. The glass, the frame and the members that stiffen the assembly all share the job. It is a structural requirement, addressed in South Africa through SANS 613 and the structural provisions behind the building regulations.

Wind loads on aluminium windows in exposed South African locations

Why building height matters

Wind speed generally increases with height above the ground, so a window high up on a multi-storey building sees a bigger load than the same window at ground level. That is why the storey a window sits on is part of its specification. A design that is comfortable on the ground floor of a house may be under-specified for an upper floor of a taller building.

Why location and exposure matter

A pair of heavy-duty automatic sliding doors designed for an industrial facility in South Africa, featuring thick frameless glass panels reinforced with slim black aluminium profiles and a powerful overhead operator encased in a matte charcoal housing. The doors open onto a spacious warehouse interior with neatly arranged shelving and polished concrete floors. Cool, diffused daylight enters through high clerestory windows, creating crisp reflections along the glass and faint elongated shadows on the floor. Captured from a wide, eye-level perspective with strong depth of field, the image emphasizes durability, precision, and safety. The photographic realism style is clean and modern, with bold geometric lines and a balanced, businesslike atmosphere.

Where the building is, and how exposed it is, change the load dramatically. Coastal and open, windswept sites experience stronger winds than sheltered inland suburbs; a building on an exposed ridge sees more than one tucked between others. These geographic and exposure conditions feed directly into the design pressure — which is why the same aluminium system genuinely cannot be applied to every opening without checking the conditions.

Why mullions and transoms change with size

As an opening gets wider or taller, the mullions (vertical members) and transoms (horizontal members) that divide and stiffen it become more important. They limit how far the assembly deflects under wind and share the load back to the structure. Increase the pane size and the required member sizes, glass thickness or support usually increase too. This is why large openings are engineered, not simply scaled up.

Mullions and transoms sized for wind load on large aluminium openings
Elevation drawing of a Coetz 2400 x 600 mm fixed aluminium window with 1 fixed pane

When large panes need specialist design

Big panes, tall facades and exposed sites can push an assembly beyond a standard solution, calling for specialist design or a competent person. The practical takeaway: never assume a large or exposed window is fine because a smaller one was. The glass thickness, frame, mullions and fixings should be confirmed against the wind load for that specific building — see our glass thickness guide for the related factors.

Wind loads and aluminium windows: the takeaway

Elevation drawing of a Coetz 2100 x 1200 mm fixed aluminium window with 1 fixed pane

The takeaway on wind loads and aluminium windows is that the load depends on the building’s height, location and exposure, and grows with opening size. Larger or more exposed openings need stronger glass, frames and mullions — so wind loads on aluminium windows must be confirmed for the specific building, not assumed.

Sources

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What this means in practice on a real project

Reading about wind loads is one thing; evidencing it on a live project is another. In our experience the difficulties almost never come from the requirement itself — they come from nobody having decided, early enough, who is responsible for the decision and who will produce the paperwork at the end. That question is worth settling at specification stage rather than at handover.

Decide who is responsible before the glass is ordered

On a supply-only order the responsibilities split. The supplier is accountable for manufacturing what was specified and for describing accurately what has been supplied. The party doing the installing is accountable for how the unit is fitted, packed and sealed. Whoever signs off the completed work is accountable for confirming that the installed result is appropriate for the application. Those are three different roles, and on smaller projects they are often three different companies, which is exactly how gaps appear.

Ask for the documentation while the job is still open

Whatever record your project needs is far easier to obtain during the contract than a year later. Keep the order confirmation showing what was supplied, keep the delivery documentation, and photograph the glass markings before the units are installed and the edges are covered by beading. Those three items answer most later questions about what was actually fitted, and they cost nothing to collect at the time.

Where Coetz™ fits in

Coetz™ supplies aluminium windows and doors glazed as standard with 6.38 mm clear laminated safety glass, and states on the order what has been supplied. Aluminium windows and doors are supplied only; automatic door systems are installed and serviced by our team. We are glad to confirm in writing what a given order contains, which is usually what a contractor or building inspector actually needs from the supplier.

An important limit on this page. The summary above is general guidance, not a compliance opinion, and it is not a substitute for the published standard or for professional advice. Requirements vary with the application, the building and the specifics of the installation. Where a decision about wind loads carries safety or regulatory consequences, work from the current published text and engage a suitably qualified competent person for your project.