There is no single correct glass thickness — it is worked out from the pane size, support, wind pressure, application and glass type together.
“How thick should the glass be?” is one of the most common questions — and one of the easiest to get wrong with a rule of thumb. The honest answer is that glass thickness selection is a balance of several factors, and the right thickness for one pane can be wrong for another that merely looks similar. This guide explains what those factors are, so you can have an informed conversation and know what must be confirmed.
Pane dimensions and support
The larger a pane, the more it flexes under load, so size is a primary driver of thickness. Equally important is how the pane is supported — whether it is held on all four edges, fewer edges, or point-fixed. A pane supported on all sides behaves very differently from one supported on two, so the same dimensions can call for different thicknesses depending on the framing.
Wind pressure, height and location
Thickness has to cope with the wind pressure the pane will see, which — as our wind loads guide explains — depends on the building’s height, its geographic location and how exposed the site is. A pane on an exposed upper floor may need to be thicker (or laminated, or otherwise upgraded) compared with the same pane in a sheltered position. This is a structural consideration under SANS 613.
Application, impact and safety
The application matters too. Glazing in a human-impact position must be a safety glazing material regardless of thickness — here the requirement is about how the glass fails, not just how strong it is. Overhead glazing, balustrades and other special applications carry their own considerations. So thickness is chosen alongside glass type: annealed, toughened or laminated, each behaving differently.
Framing and glass type
The frame and the glass type work with thickness as a set. A stiffer frame with closer support can allow a different glass build-up than a slender one; laminated units combine panes and an interlayer, changing the calculation again. This is why glass thickness cannot be pulled from a single chart in isolation — it is part of a system that includes the frame, the support and the glass type.
How thickness should be determined
Because so many factors interact, glass thickness should be determined for the specific pane, not generalised. For ordinary residential openings a supplier can specify from experience within recognised guidance; for large panes, exposed or tall buildings, facades and unusual applications, it should be confirmed against the applicable standards and, where appropriate, by a competent person. When in doubt, confirm rather than assume — and always for safety-critical positions.
Glass thickness selection in a nutshell
In a nutshell, glass thickness depends on the pane dimensions, how it is supported and framed, the wind pressure at that height and location, and any safety requirement. Because these interact, glass thickness should be determined for the specific pane and confirmed against the applicable standards, not pulled from a single chart.
Sources
Back to the Compliance Centre. Get the right spec on your project quote or browse cut-to-size glass.
What this means in practice on a real project
Reading about glass thickness 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 glass thickness carries safety or regulatory consequences, work from the current published text and engage a suitably qualified competent person for your project.
