I am thinking of adding an exempt extension to the rear of my house.
When talking about a maximum of 40 sq.m. in size, does that just include the actual internal floor space or also the external walls?
Thereis anecdotal evidence on these forums about people having obtained a Section 5 Declaration in relation to extensions to the rear which protruded to the side, but these are rare and picorette has advised you correctly.
There may be a grey area in relation to whether extending behind a front garage complies even if its not seen from the road because technically a garage isn't part of the house in terms of residential use.
There are several other issues of a technical nature in the legislation.