Specifiers’ FAQs on glass and glazing

Phil Brown, technical advisory service manager at Pilkington United Kingdom Limited, a member of the NSG Group, answers some of the questions he gets asked most frequently by glazing specifiers.

We have a south facing building. What glazing would you recommend? We need solar control glass, but don’t want a tint.

Heat build up can be a big issue in buildings that have large glazed areas, especially if they are south- or west-facing. This happens when too much of the sun’s energy streams in through the glass, raising the temperature inside in the same way as a greenhouse.

It’s possible to combat this with a solar control coating, which is designed to filter out the invisible but high-energy near infrared radiation that carries much of the heat energy in sunlight.

This means spaces can still be filled with daylight, but that the over-heating effect is reduced and, where previously solar control glass would require a heavy tint to work, advances in coating technology mean it can now be specified as a clear or neutral pane.

The Pilkington Suncool range offers glass that will significantly reduce the amount of solar energy entering the building while maintaining a natural appearance, so occupants will still enjoy great views out of the windows.

What’s the difference between toughened and laminated glass, and what does the term ‘resistance to manual attack’ mean?

Toughened glass is manufactured by subjecting final size, edge-worked panes of glass to a heating and cooling treatment whereby high compressive stresses are set up at the surfaces with balancing tensile stresses in the centre. It can deliver glass that is up to five times stronger than ordinary annealed glass.

Toughened glass can also help reduce the likelihood of injury in the event of shattering as it breaks into small, blunt-edged pieces.

Laminated glass is made up of multiple layers of glass held together by an interlayer, typically polyvinylbutyral (PVB). When impacted, laminated glass is designed to remain intact or to break safely in such a way as to reduce injury. It is typically used in applications such as glazed roofs, canopies, shopfronts and floors.

By varying the number and thickness of glass and interlayers, laminated glass can be employed in a wide range of security applications, including where resistance to manual attack is required. The European Standard which covers these applications is EN 356. It specifies a test method for security glazing design to delay access of people or objects through the glazing for a short period of time. Laminated glass can be designed to provide a range of security performance, from the lowest Class P1A to the highest class P8B.

For the most heavy-duty applications, panes of toughened glass can be laminated together.

For a project in a conservation area, can I upgrade from single to double glazing?

Upgrading glazing can be a challenge in properties located in conservation areas – where planning restrictions around altering the external appearance are tighter than is normally the case – as it can have such a major effect on the way a building looks.

The change in framing design required to install traditional double-glazed units, for example, often falls outside of what planning conditions allow.

However, it is not impossible to upgrade to double glazing.

Traditional double-glazed units (DGUs) often cause difficulties as the framing required will be thicker than those used in traditional single glazing, or the sight-lines will be visible above the beads.

However, it is worth checking with the planning officer, as they may be happy to agree a design if it is in the right material and colour scheme.

If this is not possible, another option is a product such as Pilkington Spacia, a vacuum insulating glass that uses a vacuum rather than an air- or gas-filled cavity to deliver the same benefits as a high-performance DGU in the same thickness as single glazing. As sound transmission through a vacuum is lower, superior acoustic performance can also be achieved.

This will allow you to create windows that are visually almost identical to single-pane designs while enjoying all of the energy and acoustic benefits of double glazing.