Do I Need Planning Permission for an Extension? A 2026 Homeowner Guide

Many house extensions in England do not need a full planning application. They are allowed under permitted development rights, granted nationally by the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended). But permitted development has firm limits on size, height, and position, and several common situations remove it altogether. Stay inside the limits with none of the exclusions applying, and you can build without a planning application. Go beyond them, and you need householder planning permission.

The only way to be certain for your own property is to check its planning history and designations. If you want legal certainty, you can apply to your council for a Lawful Development Certificate. A Homeowner Planning Review checks the constraints on your home for £249, in plain English, before you commit to a design or pay an architect.

Permitted development (PD) means the government has granted planning permission in advance, as long as your project meets a set of conditions. It is not a free pass. Exceed any one of the size or height limits, or trigger one of the exclusions further down this guide, and the PD right falls away, leaving you needing a full householder application.

Source: the Planning Portal and the General Permitted Development Order 2015 (as amended). These are national limits at the time of writing.

The deeper projections (8 metres for a detached house, 6 metres for any other house) are only available through the Larger Home Extension route, set out in Schedule 2, Part 1, Class A, paragraph A.4 of the General Permitted Development Order. You must apply to the council for prior approval first. The council notifies your adjoining neighbours under the neighbour consultation scheme, and if any of them object, the council decides whether the effect on their amenity is acceptable. Prior approval is not the same as a full planning permission, but it is a required step, and you cannot start a larger extension until the process is complete.

A single-storey side extension can be permitted development if it is no more than half the width of the original house, no more than 4 metres high, and single storey only. Side extensions are more tightly controlled than rear extensions, and they are removed entirely on designated land (covered below).

A two-storey rear extension can be permitted development, but it must not extend beyond the rear wall of the original house by more than 3 metres, and it must not come within 7 metres of the boundary opposite the rear wall. No extension may be higher than the highest part of the existing roof, or higher at the eaves than the existing eaves. Two-storey extensions are also removed on designated land.

Across everything above, no more than half the area of land around the original house may be covered by extensions and outbuildings combined. If a previous owner already extended the house or added a garden building, that counts against your allowance.

The limits are measured against the original house, meaning the house as it was first built, or as it stood on 1 July 1948 if it is older than that. Any extension a previous owner added reduces what you can still do under permitted development today.

Even when your extension is permitted development and needs no planning application, it will almost always need Building Regulations approval, which covers structure, fire safety, insulation, drainage, and energy performance. The two systems are separate. Clearing one does not clear the other.

If you want proof that your project is lawful permitted development, you can apply to your council for a Lawful Development Certificate. It is not compulsory, but it gives you a formal document confirming the works are lawful, which is valuable when you come to sell, as buyers and their solicitors often ask for one.

Most homeowners discover a constraint only after they have paid for drawings. A Homeowner Planning Review checks your property against the designations and planning history that decide all of this, in plain English, for £249 in 48 hours, and tells you whether you are likely on a permitted development or a full application route. We also set out how we verify every report. For the wider picture, read our guide to permitted development rights.