The enlargement of a dwellinghouse (including the erection of an extension or conservatory).
Conservatories are considered as an extension for the purposes of Permitted Development and as such a conservatory may be erected under certain conditions, provided that the area does not exceed 15sqm beyond that of the original house when first constructed.
a) the general conditions applicable to Section A (page 15 refers);
b) the floorspace (measured externally) of the extension must not exceed 15sqm beyond that of the original dwellinghouse;
c) the extension must not exceed 4 metres in height above ground level;
d) no part of the extension may be nearer to any highway which bounds the curtilage of the dwellinghouse than
i) that part of the dwellinghouse nearest to that highway, or
ii) 20 metres,
whichever is the nearer,
e) no part of the extension may be nearer than 1 metre to the boundary of the curtilage of the dwellinghouse;
f) the external finish of any walling must match that on the major part of the dwellinghouse; and
g) operations within this class are allowed only if, on completion of the operations, at least 2 car parking spaces remain within the curtilage of the dwellinghouse.
For the purpose of paragraph (g) the minimum size permitted for a car parking space is 6 metres by 3.25 metres.
Click this link to download the full order, Class 14 Page 16 refers.