When this route is relevant
The ordinary single-storey rear-extension depth limits are 3 metres for an attached house and 4 metres for a detached house. The larger-extension procedure is relevant to proposals beyond those depths, within the 6-metre or 8-metre maximum respectively. Measure from the relevant original rear wall, not simply from an existing later addition. [1][3]
This route is not available to flats or maisonettes. It is also excluded on article 2(3) land, which includes conservation areas, and on Sites of Special Scientific Interest. Check rights removed by planning conditions or Article 4 directions before relying on it. [1][4]
A larger depth does not relax everything else
The extension must remain single-storey and no more than 4 metres high. The other relevant limits still apply, including the 3-metre eaves limit within 2 metres of a boundary, restrictions on side extensions and the curtilage-coverage test. A side-return or wraparound element can therefore prevent a proposal qualifying even when its rear depth is within the headline allowance. [3][1]
Existing enlargements which the proposal joins also matter. The assessment cannot disregard a previous extension merely because it was built under a separate planning permission. [1]
The process, step by step
- Confirm eligibility and prepare the drawings. Establish the original house and show the proposal's rear projection, eaves height and overall height. Identify existing enlargements relevant to the assessment. [2]
- Apply before beginning. Supply the required written description, plan, adjoining-property addresses and applicant details, together with the applicable fee. The procedure is not a retrospective approval route for an extension already started. [2]
- Allow neighbour consultation. The council notifies adjoining owners or occupiers, including properties sharing a boundary at the rear, and gives at least 21 days for representations. [2][5]
- Establish the outcome before starting. The procedure allows work after written confirmation that prior approval is not required, after prior approval is granted, or following the prescribed 42-day period without notification, provided the legal requirements are met. [2]
An adjoining objection is not a veto. It causes the council to assess the impact on adjoining amenity under this procedure. A scheme which fails a permitted development limit does not become eligible because nobody objects. [2]
Current fee and changes to watch
From 1 April 2026, the national application fee for this larger home-extension prior-approval route is £249. This is the statutory application fee, not a price for preparing drawings or delivering the project. [6]
Fee reforms have been proposed, with 8 December 2026 recorded by Parliament as the intended commencement date. Use the made regulations and final fee schedule applicable on your submission date. The existing annual-indexation mechanism also needs checking for submissions from 1 April 2027. [7][8][9]
Build the scheme established by the procedure
Keep the submitted plans and written outcome together. Development must follow the relevant submitted or approved details, subject to the procedure's provisions for written agreement to changes. Do not assume that a deeper wall, higher roof or extra side element is covered by the earlier application. [2]
Building regulations and any Party Wall Act requirements remain separate. Resolve them before treating the planning outcome as authority to begin construction. [10][11]