Know your glass when choosing overhead glazing

Richard Burgess, Managing Director of patent glazing and roof light manufacturer Lonsdale Metal Company Ltd, has analysed the considerations for selecting glass, including costs, thermal and solar performance and safety.

Safety is the most paramount factor in overhead glazing, with the below table summarising how the varying type of glass comply with current Building Regulations.

Occasionally, it is desirable to use Wired Glass in double glazed combinations but a high risk of breakage exists because of the thermal stress. Therefore, advice ought to be requested from the sealed unit manufacturer.

Toughened glass should not be used in single glazing or to the inner pane of double glazed units in instances such as swimming pools, food & beverage preparation units or anywhere in which the small broken pieces that come with this glass type could cause injury by contamination.

Laminated glass or polycarbonate are recommended for these scenarios.

In terms of double glazing, the outer pane should typically always be toughened glass. When it comes to performance, the following features to consider include:

Low-e coating; improving thermal efficiency by retaining more heat within the building.

Tinted anti-sun glass can be used as the outer pane when combined with a laminated low-e softcoat glass, giving the benefit of reducing solar heat gain in the summer months at a decent cost. 

Neutral solar control glass features a special coating which provides enhanced solar control and gives a more neutral appearance, in colour with a slightly grey/green tint. 

All these glass types can be combined in triple glazed units, achieving both improved sound insulation and low U-values.

For large pane rooflights, the most economic glass tends to be 4-6mm thick, which rarely can be installed wider than 1000mm. However, the current trend for is seeing single pane rooflights installed up to 3m x 6m in one pane of glass, which calls for specialist manufacturing and installation by experienced companies with the necessary handling equipment and expertise.