Do I need extension planning permission is probably the question at the top of your list.

There are many factors that influence extension planning permission but the good news is that extensions are classed as Permitted Development and as such, extension planning permission will NOT be required, subject to the following conditions. (If you wish to find more information about these detailed aspects of extension planning permission, visit the Planning Portal website.)

• No more than half the area of land around the "original house" can be covered by an extension
• No extension must sit forward of the principal elevation of your home, or the side elevation if fronting a highway.
• Your extension must not be higher than the highest part of the existing roof.
• A single-storey rear extension must not extend beyond the rear wall of the original house by more than three metres if an attached house (such as a terraced or semi-detached) or by four metres if a detached house.
• (regarding the point above about extension planning permission, increased limits of 4m and 8m respectively apply up to 30^th May 2019 with regard to designated land and sites of special scientific interest. (subject to the prior notification of the proposal to the Local Planning Authority and the implementation of a neighbour consultation scheme. If objections are received, the proposal might not be allowed.)
• The maximum height of a single-storey rear extension on your home must be no more than four metres or extension planning permission will apply.
• Extensions of more than one storey must not extend beyond the rear wall of the original house by more than three metres.
• There is a maximum eaves height of three metres for an extension that sits within two metres of the boundary or extension planning permission will apply.
• The maximum eaves and ridge height of any extension must be no higher than that of the existing house.
• If you are wanting to add an extension to the side of your property, this must be a single storey with a maximum height of four metres and width no more than half that of the original house.
• For two-storey extensions, they must sit no closer than seven metres to rear boundary.
• If your extension is higher than one storey, the roof pitch must match that of the existing house.
• Any materials used in the building of your extension must be similar in appearance to the existing house – e.g. red brick, render.
• No verandas, balconies or raised platforms.
• Any windows on an upper floor of an extension that is side facing must have obscure glazing and any opening must be at least 1.7m above the floor.
• On designated land, there is no permitted development for rear extensions of more than one storey.
• On designated land, no cladding of the exterior of an extension is permitted or extension planning permission will apply.
• On designated land, no side extensions are allowed.