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Replacement windows, doors, roof lights and roof windows

From March 2003 all replacement window installations will come within the scope of the Building Regulations. From then, anyone who installs replacement windows, doors, roof lights and roof windows will have to comply with strict thermal performance standards. You can install wood, metal or PVCu windows providing they are draught-proofed and give reasonable thermal insulation.

If you are not covered by the exemption afforded under the Building Regulations 2014 Schedule 2 Class 7 for this type of work, subject to compliance with Part L1 of the Schedule 1 of the same, a full application for Building Regulations must be made.


You must have double glaze unless the building is an historic building or in conservation area and you must replace the windows to match the existing to comply with planning legislation, in which case there is some flexibility.

You must use a low emissivity glass such as Pilkington K on the inner pane. The air gap between the panes of glass must be at least 16mm.

The glazing in conservatories should be low E glass and the conservatory is separated with a wall and a door from the rest of the house. The heating in the conservatory must have separate heating controls from the rest of the house. If you don't want to use low E glass you may be able to use triple glazing, i.e. three panes of glass.

Safety glass

Safety glass, toughened or laminated must be used in all doors. Also all windows within 800mm of the floor must be safety glass to cope with the weight of someone falling against it, further measures may be necessary to deal with the risk of anyone falling from low level window openings.

The same regulations apply if more than half of the door and frame, including the fanlight, is glazed. Any glazing in the door or door side panel should be safety glass, unless the panes are less than 250mm wide.

Care must be taken with the threshold of the door. The upstand can be dangerous and this should be discussed with your customer. An upstand can be particularly difficult for people with wheelchairs and pushchairs. Many modern homes have a ramped or level entrance and in these cases a door threshold with an upstand should not be used.

Other things to consider

Opening windows - The room will need ventilation, so an opening window is needed. The opening window needs to be at least the size of the existing opening or not less than 1/20th of the floor area of the room. You also need to put in ventilation for any gas fires or boilers in the room. Check to see if the room already has air bricks installed, otherwise you will need to put in some fixed vents in the windows. It is also necessary to have 'trickle ventilators' to avoid condensation.

Fire safety - You need to talk to the Building Control Officer about fire safety and means of escape in case of fire. You may need to have 'means of escape windows' especially upstairs or from rooms that do not have direct access to a hallway or external door.

Cleaning the windows - You need to consider the means of cleaning the windows - can a ladder be used outside by a window cleaner, or will 'tilt and turn windows' be better. Can you reach the windows to open them?

For further information or to discuss any aspect of the Building Regulations, please contact us: 

DEFA Planning and Building Control

Murray House

Mount Havelock


Isle of Man


Telephone:+44 1624 685950

Email:Send Email

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