Glazing Information

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Glass and Glazing

The uses and characteristics of glass are now vast and ever increasingly ingenious. The humble piece of 4mm brittle green house glass is now a potentially highly sophisticated component for any building.

The standard thickness of float glass tends to range between 4mm and 6mm however the instances where single glazing is used in new windows are now relatively rare. Regulations, particularly part L of the current building regulations, require glazing to have a minimum thermal resistance, thereby giving a degree of energy retention. Double glazing began in the 1960's with a street of domestic houses replacing their windows with PVCu units. This was partly to replace rotten timber windows frames with PVCu window frames and partly for the parallel benefit of the double glazed units.

The standard double glazed unit, (sometimes known as an I.G.U. or Insulating Glazed Unit) comprises of two panes of glass with a space between them created by an aluminium space bar. The unit is then specified as a 4:6:4 or 4:20:4 reflecting the pane thicknesses and air space. The insulating properties of the unit are provided by the sealed air space between the units. Insulation can be enhanced if a vacuum is created to form an 'evacuated unit' or if Argon or Krypton gas is used to fill the void. In all units a dessicant is used in the perimeter safety bar to ensure no moisture is present within the unit.

If the sealant which bonds the unit together breaks down a permanent mist or water vapour is visible within the unit. It is therefore vital to purchase units from reputable manufacturers who specialise in the manufacture of sealed units and who use the correct machinery required. Poorly made units can have a life span of under 3 years.

The thermal properties of glass generally, whether single or double glazed, can be improved by the use of low emissivity glass (low-e) or Pilkington K glass. Through a hard, durable pyrolitic coating the glass is designed to transmit the maximum possible amount of visible light, absorb and reject the maximum amount of solar infra red energy, and reflect the maximum amount of long wave (room temperature) infra red energy (far I.R.). A wide range of glass coatings are available that allow for tinting and solar protection.

Where glass is likely to come under impact such as in doors, it is vital to use laminated safety glass or toughened glass. 'Laminated safety glass' is typically stocked from 6.4mm thick to 10.8mm thick. Whilst being considerably more durable than ordinary float glass, if it does break, laminated glass normally breaks in a relatively restricted manner like a car windscreen and thus is a very safe choice. 'Toughened glass' has similarly strong properties but requires a heat treatment in a furnace to achieve a toughened state.

For high levels of protection and security; impact resistant and ballistic glass are available. These are typically used in banks, jewellery shops and any anti-bandit situations. Usually such glasses are made up of various layers bonded together by transparent resins in thicknesses up to 55mm. 'Tego' is one such glass and although totally transparent it is virtually indestructible. Certain categories of anti bandit glass are rated against penetration by handguns and rifles.

Increasingly fire rated glass, known as Pyro Glass, is used in commercial applications where fire protection is required but with a minimum degree of intrusiveness. Whilst standard Georgian wired glass is relatively inexpensive it typically gives only half-hour fire protection Any glass affording one hour fire protection or above becomes extremely expensive. Glass fire ratings are specified as 30:30; 60:60 and 120:120.

As well as shop fronts, recent years have seen increasing use of glass in structural glazing, and frameless curtain walling. The introduction of CNC machinery to precision cut glass to any thickness creates the opportunity for bolted on stainless steel cleats, brackets and supports. Heavy glass for balconies and balustrades has become commonplace in many upmarket shopping centres whilst glazed stair treads are no longer uncommon in the best state-of-the-art residential homes. For detail and interior design features, glass blocks are also often used in walling solutions.

The Construction Centre.co.uk, in addition to the information above, has links to many other uses and supplies of glass such as stained glass, curved glass, secondary glazing etc.