Planning a glass extension or conservatory

A glass room at the back of a house can bring the garden a little closer.

Whether it is called a conservatory, an orangery or a glass box, planning one well starts with a few plain questions. The main ones are how it joins the house and how it is heated.

These notes follow the rules for houses in England. Wales may differ, and Scotland and Northern Ireland have their own.

Planning permission

A conservatory falls within the same planning rules as any other extension. Many can be built under permitted development rights, without a planning application, if every limit is met.

The rights apply to houses only, not to flats or maisonettes. Your council may also have removed them in your area. If the work adds more than 100 square metres of floor space, it may be liable for the Community Infrastructure Levy.

When a conservatory is exempt from building regulations

Building regulations generally apply to an extension. The Planning Portal says a conservatory is normally exempt when all of these hold.

It is single storey, at ground level and under 30 square metres in floor area.
External quality walls, doors or windows separate it from the house.
It has its own heating, with separate temperature and on and off controls.
Its glazing and any fixed electrics meet the building regulations.

A new structural opening between the conservatory and the house needs approval, even when the conservatory itself is exempt. The Planning Portal also advises against a conservatory that would block ladder access to escape windows in a loft room.

When the glass room becomes part of the house

The energy guidance for England says a conservatory must be thermally separate from the house. If that separation is taken away, or the house heating is extended into it, it is treated as an extension.

An extension has a limit on glazing. The total area of windows, roof windows, rooflights and doors should not exceed 25% of the extension's floor area. You can add the area of any windows and doors the extension covers up or removes.

There are other ways to show the extension complies. One compares the heat loss of the whole extension with one that meets the limit. Another uses the Standard Assessment Procedure for the whole home. A designer or building control body can tell you which suits your plans.

Safety glass

Glass in a critical area should be safety glazing. The Planning Portal gives a general guide to where that is.

Any panel up to 800mm from the floor.
Any glazed door up to 1500mm from the floor.
Any side panel within 300mm of a door, up to 1500mm from the floor.

Staying comfortable in summer

England's building rules on overheating apply to new homes. They do not apply to extensions or conservatories added to a home after it is built.