Just in case you needed more clarification on the small print of permitted development, here's the Ts and Cs, according to the Planning Portal!
An extension or addition to your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:
No more than half the area of land around the "original house" would be covered by additions or other buildings.
No extension forward of the principal elevation or side elevation fronting a highway.
No extension to be higher than the highest part of the roof.
Single-storey rear extensions must not extend beyond the rear wall of the original house* by more than eight metres if a detached house; or more than six metres for any other house.
If the house is in Article 2(3) designated land* or a Site of Special Scientific Interest, this limit is reduced to four metres if a detached house; or three metres for any other house.
Maximum height of a single-storey rear extension of four metres.
Extensions of more than one storey must not extend beyond the rear wall of the original house by more than three metres.
Maximum eaves height of an extension within two metres of the boundary of three metres.
Maximum eaves and ridge height of extension no higher than existing house.
Side extensions to be single storey with maximum height of four metres and width no more than half that of the original house.
Materials to be similar in appearance to the existing house.
No verandas, balconies or raised platforms.
Upper-floor, side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor
The permitted development allowances described here apply to houses and not to:
Flats and maisonettes
Converted houses or houses created through the permitted development rights to change use
Areas where there may be a planning condition, Article 4 Direction or other restriction that limits permitted development rights.
More info on the planning portal here.
To talk through your ideas or clarify Permitted Development in relation to your own plans, please email me to arrange a call at your convenience...