The Town and Country Planning (General Permitted Development) Order 1995

“A.1    Development not permitted

Development is not permitted by Class A if—

(a) the cubic content of the resulting building would exceed the cubic content of the original dwellinghouse—

(i) in the case of a terrace house or in the case of a dwellinghouse on article 1(5) land, by more than 50 cubic metres or 10 %, whichever is the greater,

(ii) in any other case, by more than 70 cubic metres or 15%, whichever is the greater,

(iii) in any case, by more than 115 cubic metres;

(b) the part of the building enlarged, improved or altered would exceed in height the highest part of the roof of the original dwellinghouse;

(c) the part of the building enlarged, improved or altered would be nearer to any highway which bounds the curtilage of the dwellinghouse than—

(i) the part of the original dwellinghouse nearest to that highway, or

(ii) any point 20 metres from that highway,

whichever is nearer to the highway;

(d) in the case of development other than the insertion, enlargement, improvement or other alteration of a window in an existing wall of a dwellinghouse, the part of the building enlarged, improved or altered would be within 2 metres of the boundary of the curtilage of the dwellinghouse and would exceed 4 metres in height;

(e) the total area of ground covered by buildings within the curtilage (other than the original dwellinghouse) would exceed 50% of the total area of the curtilage (excluding the ground area of the original dwellinghouse);

(f) it would consist of or include the installation, alteration or replacement of a satellite antenna;

(g) it would consist of or include the erection of a building within the curtilage of a listed building; or

(h) it would consist of or include an alteration to any part of the roof.