• About Double Glazing
• Glass Types
• Glass Care
• Glass Staining
• Guide To Glass Selection
• History Of Glass
• How Glass Is Made
• Types Of Windows
• Window Frames
• Window Styles
• Sash Windows Problems
• General Window Problems
• Broken Windows
• The Glazing Industry

What is double glazing?

Double glazing is now the standard fitting on modern window replacements. Instead of a single sheet of glass, double glazing as the name implies, uses two. The two sheets are installed into a sash or frame with a gap between them creating a sealed unit. They are kept separated by a spacer filled with silica balls which serve to extract moisture from the air.

There are generally two types of glass used: float glass and toughened or tempered glass.Float glass is the standard design of glass used in smaller sealed glazing units, usually located higher up in buildings where there is less chance of them being broken.Tempered glass is a safety glass that shatters into smaller, less harmful fragments when broken. It is a requirement of the Glass and Glazing Federation that toughened glass be used in larger double glazed sealed units like patio doors.

Why install it?

There are many benefits of double glazing installations versus single glazing which is why the majority of window replacements undertaken are double glazed. The safety aspect is significant, particularly in family homes. Standard single glass windows contain a single glass sheet which if hit has a tendency to break into long and potentially dangerous shards.

The main sales pitch for double glazing however usually relies on its insulating qualities. Our homes can lose up to 25% of their heat through the windows, but the double layer of the glass prevents much of the heat escaping thus saving you money on your heating bill. It has the added bonuses of being more environmentally friendly as your home will waste less heat, and also in reducing noise levels.

Double glazing is even more efficient if the gap between the two panes is slightly larger, and if argon is used to fill the space instead of air. Argon has a lower convection than oxygen and nitrogen found in the air. A low emissivity (Low E) coating can also be applied to the glass which allows heat into the building but prevents it from leaving.

The insulation value of double glazing is measured the value U, standing for the measurement of heat transference through the glass. U is worked out by assessing the unit gap size, whether it has air or argon, and whether it has a Low E rating like Pilkington K glass.

Triple glazing - Triple glazing introduces a third piece of glass creating a second sealed unit into the window. It provides even greater energy savings and increased sound insulation, and as such is generally installed on homes under flight paths or other highly noisy locations. However, triple glazing costs around 20-40% more than double glazing and inevitably weighs more.