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Red tick
Red tick

If you are ever unsure, it is always best to consult with a builder or surveyor just to double check that your replacement windows fall within these boundaries. We are more than happy to offer help and advice regarding your replacement window requirements or upcoming projects.

UPVC window

Before the toughening process, toughened glass is essentially regular or ‘float’ glass. When broken, float glass will break into pieces and can be extremely sharp making it impractical and dangerous to use for all windows. Before undergoing the toughening process, pieces of glass are made to the specific sizes of the window that requires it as toughened glass one complete cannot be cut to size.

When cut to size, the glass is then subjected to a heating and cooling process whereby the surface of the glass is exposed to a high temperature and then rapidly cooled. This process causes the surface to contract whilst also causing tensile stresses in the centre part of the unit. It is this process that enables the finished piece of glass to be up to 5 times stronger than the original float glass whilst retaining the colour and performance aspects of the glass. This process also ensures that when broken the glass shatters into small, blunt fragments.

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When considering replacing your existing windows there is a chance that at least some or part of the replacements will require toughened or safety glass. Toughened glass requirements fall within approved document K of the building regulations and is there to ensure that areas of glass that are considered to be at risk if they are knocked or fallen into break as safely as possible.


The approved document K states that in order to pass the impact test and become a safe breakage the glass must break into separate pieces that are not sharp or pointed. The idea of this is that if a breakage does occur, the glass will not break into tiny sharp pieces and cause harm.

Any piece of glass that is within 800mm from floor level

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When is toughened glass needed?

What is toughened glass?

Toughened glass locations

Any piece of glass that is within 300mm of a door that is also 1500mm from floor level

Toughened Glass

As the image indicates, glass in areas 2, 4, 5, 6, 7, 8 and 11 all are required to be toughened as they are deemed to be in critical locations. Even if parts of the unit fall within these locations, the whole unit must be toughened.

The key areas that require toughened glass are as follows:

The shaded areas in the image below indicates where toughened glass is necessary to comply with building regulations: