Do You Need Planning Permission for a House Extension?

Under the Town and Country Planning (General Permitted Development) (England) Order 2015, a significant range of house extensions can proceed without planning permission. The key permitted development conditions for single-storey rear extensions are:

• •**Terraced and semi-detached houses**: up to 4 metres depth from the original rear wall
• •**Detached houses**: up to 8 metres depth from the original rear wall
• •Maximum height at the eaves: 3 metres (within 2 metres of a boundary)
• •Maximum overall height: 4 metres
• •Materials must be similar in appearance to the existing house
• •No more than half the garden area is covered by extensions

These limits apply to the original house — meaning the house as it was first built, or as it stood on 1 July 1948 if built before that date. Any extensions already built count towards the Permitted Development allowance.

In 2013, the government introduced the Householder Prior Approval scheme — sometimes called the Neighbour Consultation Scheme — which allows larger single-storey rear extensions to be built without full planning permission, subject to a neighbour consultation process.

• Under Prior Approval:
• •**Terraced and semi-detached houses** can build up to **6 metres** (rather than 4 metres)
• •**Detached houses** can build up to **8 metres** (the same as standard PD, but confirmed via the Prior Approval route)

To use Prior Approval, you must notify the council before work starts. The council then consults your immediately adjoining neighbours. If they raise objections, the council assesses the impact. The whole process takes up to 42 days.

Important: Prior Approval is not planning permission. If the council raises no objections, you can proceed. If they do, you may need to reduce the depth or apply for full planning permission.

Full planning permission is required in the following situations:

• **Property type**
• •Flats and maisonettes — Permitted Development does not apply
• •Listed buildings — require Listed Building Consent in addition to planning permission
• •Properties in Conservation Areas, National Parks, AONBs, or World Heritage Sites — PD rights are restricted

• **Design and scale**
• •Any extension that exceeds the PD depth limits (even by a small margin)
• •Two-storey or double-storey rear extensions
• •Side extensions that exceed half the width of the original house
• •Side extensions in Conservation Areas that front a highway
• •Any extension that covers more than half the garden
• •Anything that exceeds height limits

• **Local restrictions**
• •Properties subject to an Article 4 Direction (the council has removed PD rights)
• •Some new-build estates have PD rights removed via planning conditions

Always check your title deeds and call your local planning authority before assuming PD applies.

Double-storey rear extensions almost always require planning permission. There is no Permitted Development route for two-storey rear extensions.

The reason is their greater impact: a two-storey extension increases the bulk of the property significantly and its height means it overshadows neighbouring properties and gardens to a greater degree.

• For a double-storey extension you will need:
• •Full planning application with drawings
• •The council's 8-week decision period (often longer in practice)
• •A design that responds to the character of the area and the impact on neighbours

In London, many boroughs have published Supplementary Planning Documents (SPDs) or design guidance on extensions that go beyond national PD rules. Islington, Hackney, Camden and others can be more restrictive than the national baseline.

Side extensions are the most complex area from a planning perspective. The Permitted Development rules for side extensions are strict:

• •A single-storey side extension may be Permitted Development if it does not exceed **half the width of the original house**
• •It must be **single-storey only** (maximum 4 metres high)
• •In **Conservation Areas**, any side extension that is forward of the principal elevation or fronts a highway requires planning permission
• •Corner plots: properties on corner plots almost always require planning permission for side extensions

A common scenario: a homeowner in a Conservation Area wants to extend to the side. Even if the width is within the PD limit, if the property is on a corner or the side extension is visible from the street, planning permission is likely required.

A wrap-around extension combines a rear extension and a side return extension into an L-shape. This is extremely popular in London terraces where the side return (the narrow passage beside the house) can be enclosed.

• From a planning perspective, a wrap-around extension is assessed as two separate elements:
• •The rear element: assessed against PD rear extension rules
• •The side element: assessed against PD side extension rules

In many cases, the rear part of a wrap-around will be PD, but the side part may require planning permission — particularly if you are in a Conservation Area, on a corner plot, or the side element exceeds the width limit. Each case is property-specific.

Many London boroughs take a specific view on wrap-around extensions. A pre-application enquiry to the council (£50–£300) is well worth it before committing to drawings.

A Lawful Development Certificate (LDC) confirms in writing that your extension is lawful as Permitted Development. It is not planning permission — it confirms permission is not required.

• You should obtain an LDC when:
• •Your extension falls within PD limits and you want written certainty
• •You are planning to sell the property and solicitors will ask for evidence
• •You have a mortgage lender who requires documented confirmation
• •You want protection against any future planning enforcement action

An LDC costs £206 per application in England (2025). The council has 8 weeks to decide. RCB assists clients through this process as part of our pre-construction service — we submit the drawings and manage the process so you don't need to.

This is one of the most important points homeowners miss: **Planning permission and Building Regulations are completely separate.**

Even if your extension is Permitted Development and requires no planning permission whatsoever, Building Regulations approval is always required. This is not optional.

• Building Regulations cover:
• •Structural stability (foundations, beams, connections)
• •Thermal insulation and energy performance (Part L)
• •Ventilation and moisture control (Part F)
• •Fire safety
• •Electrical installation (Part P)
• •Drainage connections

Without a Building Control completion certificate, you will face problems when selling the property, and your building insurer may not cover the extension. RCB manages all Building Control notifications and inspections as part of our principal contractor service.