It is essential when considering whether a structure is a conservatory and therefore not part of the main structure of the property to understand the definition as quoted in the Building Regulations.

The structure needs to have:

· Not less than ¾ of the roof area made from translucent material, and
· Not less than ½ of the wall area made from translucent material
· Either unheated, or heated by a system with own and separate heating controls (ref. Approved Document L1 CL 1.59(b)), and
· Be separated from the main residence by "external" doors

If the structure meets this definition, in full, then it is exempt from the requirement of Approved Document L1.

Furthermore if the structure is less than 30m2 then it is generally not necessary to obtain building control approval (Ref: Schedule 2, Class vii)

It should be noted that whether or not a structure is deemed to be a 'conservatory', or an extension to a dwelling, the requirements of Approved Document N apply.

If the structure is deemed to be a conservatory then all doors and windows between the conservatory and the main residence must, when replaced, comply with Approved Document L1, and to the documents to which it refers. The conservatory is not to be registered with FENSA but replacing the dividing doors and windows needs to be.

If the structure does not meet the full definition of a conservatory it does not have an exempt status and must comply with Approved Document L1. In this situation any doors and windows between the residence and the extension will be classed as internal and exempt from Approved Document L1.