When fitting replacement double glazing or triple glazing, be the frames aluminium, UPVC or wood, it is important to ensure that you get the right type of double glazing glass or indeed particularly triple glazing glass. In the case of the latter, ensure your installer fits triple glazed sealed units with a toughened middle pane of glass, as this reduces the likelihood of the middle pane cracking as a result of thermal differences between the inner and outer panes (usually made of float glass).
The England and Wales Building Regulations state that toughened safety glass must be fitted in entrance doors, conservatories, French doors, sliding doors, patio doors, windows within 300mm of doors, windows within 800mm of the internal floor level and in bathrooms where the window is adjacent to the bath or shower. Therefore, in these situations all panes of glass in double glazing and triple glazing are required by law to be safety glass. In residential replacement and new fenestration, there are three main types of glass 1) float glass, 2) toughened glass and 3) laminated glass.
Float Glass
According to Wikipedia “Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass. Most float glass is soda-lime glass, but relatively minor quantities of speciality borosilicate and flat panel display glass are also produced using the float glass process. The float glass process is also known as the Pilkington process, named after the British glass manufacturer Pilkington, which pioneered the technique (invented by Sir Alastair Pilkington) in the 1950s.”
Toughened Glass
According to Wikipedia “Toughened or tempered glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering creates balanced internal stresses which cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards. The granular chunks are less likely to cause injury.
As a result of its safety and strength, tempered glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.”
Laminated Glass
According to Wikipedia “Laminated glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), between its two or more layers of glass. The inter-layer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the glass. “Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered.”
Toughened glass costs more than float glass, and laminated glass costs more than toughened safety glass, so ensure your double glazing installer actually fits what you expect. If the glass is toughened or laminated it will have Kite marks in one or more of the corners of the sealed unit. Most residential double glazing utilises 4mm thick float glass.
Being of a different type of manufacture, toughened and particularly laminate glass help slightly reduce noise pollution, as sound does not travel through these types of glass as easily as it does through float glass. More important than the glass type when it comes to reducing exterior noise is the gap between panes. The wider the gap, the greater the noise reduction, hence way fitting secondary glazing 100mm inside of your existing windows will deliver the optimum sound reduction.
For legal, safety and quality of living environment reasons, it is important to check that any replacement windows and doors that you have supplied and fitted do in-fact have the right glass specification. Not only that, installing the correct double glazed or triple glazed windows brings peace of mind.