Rear extension depth limits and the larger home right

The standard rear extension depth limit under permitted development is 3 m beyond the original rear wall for a semi-detached or terraced house and 4 m for a detached house, for a single storey extension. Above that, and up to 6 m and 8 m respectively, the work can still be permitted development under the larger home extension route, but only after a prior approval notification to the council and a neighbour consultation period. All of this sits in Class A of Part 1 of Schedule 2 to the General Permitted Development Order 2015, and every limit has to be met, not most of them.

Standard depth limits by house type

Measure from the rear wall of the original dwellinghouse, meaning the house as it stood on 1 July 1948 or as first built if later. An extension added by a previous owner in 1995 does not move the starting line.

Two further limits apply to both routes. The extension must not exceed 4 m in height overall. And where it comes within 2 m of the boundary of the curtilage, the eaves height must not exceed 3 m, which is the limit that catches most terraced-house schemes long before depth does.

The 50 per cent rule sits alongside them: the total area of ground covered by buildings within the curtilage, other than the original house, must not exceed half the area of the curtilage excluding the ground area of the original house. Sheds, outbuildings and earlier extensions all count towards that figure, which is why a long-extended house with a garden room can be out of permitted development before anything is drawn.

The larger extension route and its notification step

The larger home extension right is a prior approval procedure, not a free pass. Before any work starts, the developer gives the local planning authority written notice, and that notice has to contain specific information.

1. A written description of the proposed development, including how far it extends beyond the rear wall of the original dwellinghouse, its maximum height, and the height of the eaves.
2. A plan of the site showing the proposed development.
3. The addresses of any adjoining premises, meaning properties sharing a boundary including those to the rear.
4. A contact address and an email address if the applicant is content to be contacted that way.
5. The relevant fee.

The council then notifies the adjoining owners and occupiers and allows 21 days for representations. Work must not begin until the council has notified the applicant that prior approval is not required, or has granted it, or until 42 days have passed from receipt without any decision being issued.

There is also a completion step that gets forgotten. The developer must notify the council in writing as soon as reasonably practicable after the extension is finished, giving the name of the developer, the address and the completion date. It is a small administrative act and leaving it out muddies the position later.

How the neighbour consultation works

This is the part most homeowners misunderstand. The council does not reopen the design.

If no adjoining owner or occupier objects within the 21 days, the council cannot refuse on amenity grounds and the development proceeds. If an objection is received, the council considers one question only: the effect of the proposed extension on the amenity of adjoining premises. Not its appearance, not its effect on the street, not the applicant's reasons for wanting it.

That narrow scope cuts both ways. Objections about loss of light, overshadowing and an overbearing effect on a neighbouring garden or window are on the point. Objections about parking, noise during construction, drainage, or dislike of the materials are outside the scope of the assessment, though people still raise them. Where privacy and overlooking are the concern, the arguments tend to carry more weight on upper floors, and the way councils test them is set out in the piece on balconies and the overlooking test.

Height, eaves and the limits that still apply

The larger home route relaxes depth and nothing else. Everything else in Class A still applies in full.

Maximum height remains 4 m. The eaves limit within 2 m of a boundary remains 3 m. The extension must be single storey. Materials must be of a similar appearance to those of the exterior of the existing house, a requirement examined in materials of similar appearance. No verandas, balconies or raised platforms are permitted under this class, and a raised platform means anything more than 300 mm above ground level.

The extension must not extend beyond a wall forming a principal elevation fronting a highway, or beyond a side elevation fronting a highway. And it must not be higher than the highest part of the roof of the existing house.

Where a scheme fails any of these, the larger home route is unavailable and a full householder planning application is the route, whatever the depth.

Designated land and other exclusions

The larger home extension right does not apply on designated land at all. That means conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites. On that land the standard 3 m and 4 m limits are the ceiling for permitted development, and anything deeper needs planning permission.

Other exclusions bite more quietly:

• Article 4 directions, which individual councils make to remove permitted development rights in defined areas, commonly in conservation areas and sometimes across whole estates.
• Conditions on an earlier planning permission removing permitted development rights, which is standard on new housing estates and on approvals granted close to the limit of acceptability.
• Flats and maisonettes, which have no Part 1 rights at all.
• Houses created through certain prior approval routes, where the Order restricts the rights that would otherwise follow.
• Listed buildings, where listed building consent is required for works affecting the building's character regardless of permitted development.

Check the title, the planning history and the council's Article 4 map before relying on any of this. Where a side return is involved rather than a straightforward rear extension, the geometry of the principal elevation rule becomes the controlling factor, as the piece on side return infill on a Victorian terrace explains.

Evidence to submit with the prior approval

Keep it tight and factual. A site location plan, a block plan showing the extension and the boundaries with adjoining premises marked, existing and proposed floor plans and elevations at a stated scale, and a short written description covering depth beyond the original rear wall, overall height and eaves height.

Add a note identifying the original dwellinghouse and any later additions, with dates if known, because the case officer's first question is where the original rear wall sat. Where the house has been extended before, a marked-up plan showing the original footprint saves a round of correspondence.

A prior approval notification is not a planning application and does not need a full supporting statement. Where the scheme is borderline, a short planning statement explaining the amenity relationship with each adjoining property is useful, because it gives the officer something to weigh against an objection.

Where a full application is the faster route

Prior approval takes up to 42 days and the outcome is binary. A householder planning application takes eight weeks and allows negotiation.

Go straight to a full application where the scheme also involves a side extension or a change to the roof, where the house is on designated land, where permitted development rights have been removed, where the 50 per cent curtilage figure is close, or where you already know a neighbour will object on amenity grounds and the design has room to move. In those cases the prior approval is likely to fail and the time is lost.

A Lawful Development Certificate is the only formal way to confirm that works are lawful under permitted development, and it is worth having where the house will be sold or remortgaged.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. To see which documents your extension is likely to need, enter your postcode on PlanScope.