How to calculate wind load on glass

Learn the key considerations with regard to wind load on glass, including how to calculate wind load and how to specify for it.



Glass is a multifunctional material. Take a window in a high-rise building. It provides a view, a ventilation system, soundproofing, insulation and a security barrier.

Not all glass, however, is created equal. Different products fulfil different functions to greater or lesser degrees.

This is true when it comes to the issue of wind load. This is the pressure exerted on a building by the wind. To ensure structural integrity, a building needs to be designed and built with wind load in mind.

However, not all glass can absorb wind loads the same way. The ability of glass to withstand wind pressure depends on a range of factors. These include the type of glass, its thickness, its size and even the way it's installed.

In this article, we give you a whistle-stop tour of this key issue when specifying glass for a building project. We hope it helps you get the right materials for the job.

What is wind load?

The phrase "wind load" refers to the ways in which wind interacts with buildings. We say "ways", plural, because there are three main ways this happens. These are lateral or horizontal load, uplift load and shear load.

Lateral load

Lateral load is when wind pushes directly against the vertical surfaces of a building. If the building has been inadequately specified, this horizontal pressure can eventually lead the structure to crack, tilt or even fall over.

Uplift load

Uplift load is when wind flows over the roof. This can create a vacuum-style effect that "sucks up" the roof, pulling it upwards and weakening its structure. Uplift load can also occur when wind enters a building through open doors or windows and pushes the roof from the inside.

Shear load

Finally, there's shear load. Like lateral load, this is a horizontal wind pressure that twists and tears. If the right steps haven't been taken, this can stress corners and vertical surfaces.

Why is wind load important?

The main reason designers, architects and specifiers should care about wind load is that wind has the power to blow out windows, roofs and even entire structures. This is obviously undesirable for both project managers and building users.

Because of safety risks posed by buildings that don't adequately account for wind load, accurate wind load calculation is often governed by regulations and guidelines.

In the UK, wind load is regulated by BS EN 1991-1-4:2005+A1:2010 (Eurocode 1: Actions on structures – General Actions – Wind Actions). This is used in conjunction with the wind and topography data provided by the UK National Annex.

Regulations like these ensure that buildings can safely absorb the wind and transfer it to the foundations.

How do you specify for wind load in glass design?

Before specifying glass for a building, you need to calculate wind load. This calculation takes into account local wind speeds, how the local terrain affects wind pressure and the height and shape of the building.

The right kind of glass must then be specified. This involves choosing between annealed, toughened and laminated glass. You'll also need to consider whether the panes are long and narrow or square and whether they're supported on two sides or all four.

With all this taken into account, the required thickness will be covered by BS 6262-2:2005 for low-rise buildings and BS EN1991-1-4 for other kinds.

It's important to note that these guidelines are the only source that counts when calculating wind load on glass. This blog post is intended simply to point you in the right direction. The decision you make, however, should be verified by a structural engineer in line with local building regulations.

The glass should also be specified in line with deflection limits. These are serviceability criteria designed to restrict the movement of buildings. The glass specified shouldn't exceed a maximum deflection or a specific distance. These limits are specified in the UK by BS 6180:2011.

How do you calculate wind load on glass?

Calculating wind load on glass involves determining the design wind pressure (typically in kN/m^2 or PSF) based on location, building height and exposure. This is then applied to the glass area.

There's a standard formula for calculating wind load, which includes velocity pressure, gust effect factor and pressure coefficient.

Glass manufacturer Pilkington provides a wind load calculator on its website. This tool lets you assess the wind load resistance of single-glazed, annealed window glass according to the ASTM E1300 standard.

For safety glass, a common formula multiplies area by pressure by drag coefficient. Pressure is based on regional wind speeds.

For all types of glazing, a minimum wind loading of 0.6 kN/m^2 (600 N/m²) is often recommended. The calculation accounts for how the glass is supported and the frames should be designed in order to limit deflection to no more than L/175.

What kinds of glass are used for wind resistance?

There are five key types of glass for wind load: toughened glass, laminated glass, heat-strengthened glass, insulating glass units (IGUs) and laminated toughened glass.

Here at ToughGlaze, we specialise in safety glass, which covers laminated glass, toughened glass and laminated toughened glass.

Toughened glass – sometimes known as "tempered" glass – is around four to five times stronger than regular annealed glass and is designed to withstand high pressure.

Toughened glass is also manufactured in such a way that when it breaks, it shatters into lots of tiny pieces rather than harmful shards. This combination of durability and its distinctive breakage pattern qualifies it as a kind of safety glass.

Laminated glass is even stronger and can withstand even higher wind pressures. It's around six times stronger than standard annealed glass. Its structure – two panes of glass sandwiching a plastic interlayer – means it maintains structural integrity even when it breaks.

Founded in 1993, ToughGlaze is one of the UK's most trusted specialist glass suppliers. We cut, process and ship a wide variety of glass products – all under one roof. If you need high-quality, fully compliant glass for a project, don't hesitate to get in touch with our experts.