Building Regulations

Guidance for building regulations applying to windows, doors, roof lights and roof windows

To ensure that the completed installation of replacement windows etc. complies with the relevant requirements of The Building Regulations, regard should be given to the following;

Use as a Fire Escape

Air Supply and Ventilation

Safety Glazing

Thermal Insulation

Bay Windows


Means of escape in case of a fire;

Means of escape windows e.g. windows to habitable rooms in the upper storey of a building, should have a clear unobstructed opening of 0.33m² with a minimum dimension of 450mm.

Ventilation and Combustion Air

The openable area of a window with a hinge or pivot that opens 30º or more should be equivalent to a minimum of 5% of the floor area of the room. For a hinged or pivot window that opens between 15º and 30º the opening part should be at least 10% of the floor area of the room.

Where the original windows were fitted with controllable trickle ventilators the replacement windows should also include them with minimum unobstructed areas of 5000mm² for habitable rooms and 2500mm² for kitchens, utility rooms and bathrooms.

Where existing windows are not fitted with trickle ventilators it is strongly recommended that replacement windows include them to help with control of condensation and improve indoor air quality.

If an existing window or door has a permanent vent to provide combustion air to heat producing appliances, the new installation should provide at least the same amount of permanent ventilation.

Safety Glazing

Glazing in critical locations should be safety glass in accordance with BS.6206. Critical locations are defined as areas in and adjacent to doors up to 1.5m above floor level and 300m each side, and windows and locations within 800mm of the floor level.

Thermal Insulation

The openable area of a window with a hinge or pivot that opens 30º or more should be equivalent to a minimum of 5% of the floor area of the room. For a hinged or pivot window that opens between 15º and 30º the opening part should be at least 10% of the floor area of the room.

Where the original windows were fitted with controllable trickle ventilators the replacement windows should also include them with minimum unobstructed areas of 5000mm² for habitable rooms and 2500mm² for kitchens, utility rooms and bathrooms.

Bay Windows

Please not that when adding a bay window to an existing home, this will be treated in planning and building regulation terms, as an extension. If you want to convert exisitng windows into bay windows, you must get building regulation approval for that as well as the main extension.

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