Do I need planning permission for a single-storey extension?

The short answer

You may not need to make a full planning application for a single-storey extension if it qualifies as permitted development. Whether it qualifies depends on the type of property, where the extension sits, its depth and height, the amount of land already developed, and whether any local or property-specific restrictions apply.

A modest rear extension is the most likely type to fall within permitted development. Front extensions usually need planning permission, while side and wraparound extensions are subject to tighter rules.

This guide applies to houses in England. Planning rules differ in Wales, Scotland and Northern Ireland.

What counts as a single-storey extension?

A single-storey extension adds accommodation at ground-floor level only. Common examples include a larger kitchen, dining room, utility room, home office, accessible bedroom or family room.

For planning purposes, the exact shape matters. A rear extension, side extension, front extension and wraparound extension are assessed differently, even if they have the same floor area.

Single-storey rear extensions

Under the standard permitted development limits in England, a single-storey rear extension may extend beyond the rear wall of the original house by up to:

• 4 metres for a detached house.
• 3 metres for any other house, including semi-detached and terraced homes.

The extension must not be more than 4 metres high. Where any part of it is within 2 metres of a boundary, its eaves must not be higher than 3 metres.

The “original house” normally means the house as it stood on 1 July 1948, or as it was first built if it was constructed after that date. Earlier extensions count when the council assesses how far you can extend now.

Can I build a larger rear extension?

The larger home extension process can allow a single-storey rear extension of up to:

• 8 metres for a detached house.
• 6 metres for any other house.

These larger limits are not automatic. You must use the council’s prior approval process before starting work. The council will notify adjoining neighbours and consider the effect of the extension on their amenity.

Prior approval is different from a full householder planning application, but it is still a formal process. Do not begin building until the required procedure has been completed.

Single-storey side extensions

A side extension can sometimes be permitted development when it:

• Is single storey.
• Is no more than 4 metres high.
• Is no wider than half the width of the original house.
• Meets the other limits applying to the property and site.

On certain designated land, a side extension is not permitted development. Side extensions can also become more complicated where the house sits on a corner plot or has more than one elevation facing a highway.

Do front extensions need planning permission?

A single-storey extension forward of the principal elevation, or forward of a side elevation that fronts a highway, will normally need planning permission. The principal elevation is usually the main front of the house, but its identification can depend on the building’s design and setting.

A small porch has its own permitted development rules, but a larger front extension used as a room is generally assessed through a householder planning application.

What about a wraparound extension?

A wraparound extension combines a rear extension with a side return. These designs are popular on Victorian and Edwardian terraces, but they do not always fit neatly within permitted development.

Even where the rear and side parts appear to meet their individual limits, the combined design may be assessed as one enlargement. A full planning application is often the clearer and safer route for a wraparound extension.

Other permitted development limits

Depth and height are not the only tests. Your extension must also satisfy the wider conditions, including:

• Land coverage — extensions and other buildings must not cover more than half the land around the original house.
• Overall height — the extension must not be higher than the highest part of the existing roof.
• Eaves height — its eaves must not be higher than the eaves of the existing house.
• Materials — external materials should be similar in appearance to those used on the existing house.
• Raised features — verandas, balconies and raised platforms are not included within the normal house-extension rights.
• Previous work — earlier extensions and additions can reduce the remaining permitted development allowance.

When will I need planning permission?

A full householder planning application is likely to be needed when:

• The extension exceeds the relevant permitted development depth, height or width limits.
• It is positioned in front of the principal elevation.
• The design is a wraparound extension that does not comply with the permitted development rules.
• The property is a flat or maisonette.
• The building is listed, or the work affects a listed building.
• The site is on designated land where the relevant rights are restricted.
• An Article 4 direction or a condition on an earlier permission has removed permitted development rights.
• The proposed materials or appearance fall outside the permitted development conditions.

Should I get a Lawful Development Certificate?

Even where a single-storey extension appears to be permitted development, applying for a Lawful Development Certificate is often worthwhile. It gives you a formal council decision confirming that the proposed work is lawful for planning purposes.

This can reduce uncertainty before construction and provide useful evidence when the property is sold or remortgaged. The application normally needs existing and proposed plans, elevations and a site plan that clearly show the dimensions being assessed.

For a broader explanation, read our guide: What is permitted development and does it apply to my extension?

Do building regulations still apply?

Yes. Planning permission and building regulations are separate systems. Most single-storey extensions require building regulations approval even when they are permitted development.

Building control will consider matters such as foundations, structure, insulation, ventilation, drainage, fire safety, glazing and electrical work. Structural calculations may also be required where walls are removed or steel beams are introduced.

What about the Party Wall Act?

You may also need to consider the Party Wall etc. Act 1996 if the work involves building on or close to a boundary, working on a shared wall, or excavating near a neighbouring building.

Party wall requirements are separate from both planning permission and building regulations. Receiving planning permission does not remove your responsibilities under the Act.

What drawings will I need?

For a planning application, Lawful Development Certificate or prior approval submission, the usual drawing package includes:

• Existing floor plans showing the property before the work.
• Proposed floor plans showing the extension and new layout.
• Existing elevations showing the current external appearance.
• Proposed elevations showing the extension’s height, roof, doors, windows and materials.
• Location and site plans showing the property, boundaries and surrounding context.

The drawings should include clear dimensions so the council can test the design against the relevant planning rules. They also give builders a more reliable basis for pricing the project.

What should I check before starting?

• Confirm whether the property is a house, flat or maisonette.
• Identify the original house and measure from its original walls.
• Check the property’s planning history for earlier extensions and restrictive conditions.
• Check whether the site is listed, in a conservation area or covered by an Article 4 direction.
• Prepare dimensioned drawings before deciding which application route applies.
• Apply for prior approval, planning permission or an LDC where appropriate.
• Arrange building regulations approval and check whether the Party Wall Act applies.

Summary

Many modest single-storey rear extensions can be built under permitted development in England. The usual rear depth is up to 4 metres for a detached house and 3 metres for other houses, with larger extensions potentially available through prior approval.

Side extensions face tighter width restrictions, front extensions normally require planning permission, and wraparound designs need careful assessment. Property type, location, planning history, boundaries and previous extensions can all change the answer.

Accurate drawings are one of the best ways to establish whether your proposal meets the rules and to support whichever application route is required.