Permitted development (PD) rights allow homeowners to build a single-storey rear extension without applying for planning permission, subject to specific size limits and conditions. Understanding exactly what is and is not allowed under these rules can save you thousands in planning fees and months of waiting — or prevent you from building something that turns out to require permission after all.

This guide sets out the full permitted development rules for single-storey rear extensions in England as of 2025, including the larger home extension scheme, conditions that apply regardless of size, and the scenarios where PD rights are restricted or removed entirely.

The Basic Permitted Development Size Limits

Under Class A, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015, a single-storey rear extension is permitted development if it does not exceed:

• 3 metres beyond the rear wall of the original dwellinghouse for a terraced or semi-detached house
• 4 metres beyond the rear wall of the original dwellinghouse for a detached house

The “original dwellinghouse” means the house as it was built, or as it stood on 1 July 1948 if built before that date. Extensions already built since then count toward these limits — so if a previous owner added a 2-metre extension, only 1 metre more is available under PD rights (for a semi-detached house).

The Larger Home Extension Scheme (Prior Approval)

The larger home extension scheme allows single-storey rear extensions beyond the basic limits, up to:

• 6 metres for a terraced or semi-detached house
• 8 metres for a detached house

This scheme requires a prior approval application to the local planning authority. The council notifies neighbours, and if any objection is received, the council must consider the impact on amenity and decide whether to approve or refuse. If no objection is received within 21 days, the extension can proceed. This is a significantly lighter-touch process than a full planning application but is not automatic.

Height Limits

The single-storey rear extension must not exceed:

• A maximum height of 4 metres
• A maximum eaves height of 3 metres if within 2 metres of the boundary

For a lean-to or flat-roof extension built close to the side or rear boundary, the 3-metre eaves restriction is the practical limiting factor. Most single-storey extensions have eaves at around 2.5–2.8 metres with a roof above, so the 4-metre overall maximum is rarely an issue.

Materials Condition

Materials used in the exterior of a permitted development extension must be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse. This condition is often misunderstood — it does not mean identical materials, but materials that are visually similar in appearance.

In practice, a brick-built extension on a brick house should use matching or closely similar brick. A render finish may be acceptable if the existing house has rendered elements. A contemporary zinc or glass extension may not satisfy this condition on a traditional brick property without a prior approval or planning application.

Other Conditions That Apply to All PD Extensions

• No extension on land in front of a principal elevation: The extension must be to the rear, not visible from the principal road-facing elevation
• Total enlarged area must not exceed 50% of the curtilage: All existing and proposed outbuildings and extensions combined must not cover more than half the land around the original house
• No verandas, balconies or raised platforms: These are not permitted development and require planning permission even if part of an otherwise PD extension
• No extension beyond the side elevation of the original house: The extension must not extend beyond the side walls of the original house (this restricts wrap-around extensions from being fully PD)
• Roof pitch must not exceed the existing house’s roof pitch (for pitched roofs)

When PD Rights Are Restricted or Removed

Designated Areas

Permitted development rights are more restricted in:

• Conservation areas: Extensions visible from a public highway in a conservation area require planning permission. Rear extensions not visible from the road may still be permitted development, but the restriction depends on the specific elevation.
• National Parks and Areas of Outstanding Natural Beauty (AONB): Side extensions are not permitted development; rear extensions are subject to the same limits as elsewhere
• World Heritage Sites and the Broads: Similar restrictions apply
• Listed buildings: Listed building consent is required for any extension regardless of PD rights — permitted development does not apply to listed buildings

Article 4 Directions

A local planning authority can remove permitted development rights for specific areas using an Article 4 Direction. These are common in conservation areas, historic town centres, and some London boroughs. You can check whether an Article 4 Direction applies to your property by searching the local planning authority’s website or calling their planning department.

Conditions Attached to Planning Permissions

If your house was built under a planning permission that includes a condition removing or restricting permitted development rights, those conditions override the standard PD rights. This is common on new-build estates. Check the planning history of your property on the local authority’s planning portal.

Flats and Maisonettes

Permitted development rights under Class A do not apply to flats, maisonettes, or properties that have been converted from houses into flats. All extensions to such properties require planning permission.

Do I Need Building Regulations Approval for a PD Extension?

Yes. Permitted development means you do not need planning permission — it does not mean you are exempt from building regulations. Any extension must comply with the Building Regulations 2010, including structural requirements (Part A), fire safety (Part B), thermal performance (Part L), drainage (Part H), and ventilation (Part F).

You must submit a building regulations application (either a full plans application or a building notice) before work starts, and a building control inspector will visit during and after construction.

Do I Need a Lawful Development Certificate?

Technically no — if your extension genuinely meets all PD conditions, you can build it without any formal confirmation from the council. However, obtaining a Lawful Development Certificate (LDC) from the local planning authority provides written confirmation that the development is lawful. This is strongly recommended because:

• It proves lawfulness when you sell the property
• It protects you if the council subsequently disputes the PD status
• It removes ambiguity about boundary measurements or conditions

An LDC typically costs £103 for a householder application (half the planning fee) and takes 4–8 weeks to process.

Frequently Asked Questions

Does a permitted development extension affect my neighbours?

Under the basic PD limits (3m/4m), there is no formal neighbour notification requirement. Under the larger home extension scheme (up to 6m/8m), neighbours are formally notified. Regardless of planning, if your extension is within 3 metres of the neighbour’s foundations, the Party Wall etc. Act 1996 requires you to serve a party wall notice.

Can I build a single-storey rear extension if there are trees in the way?

Tree Preservation Orders (TPOs) and conservation area tree protection are separate from planning permission. If a protected tree stands within the footprint of your proposed extension, you will need consent to remove or prune it before or during construction, regardless of whether planning permission is needed for the extension itself.

Does the 3-metre or 4-metre limit include the wall thickness?

The depth is measured from the original rear wall of the house to the furthest external face of the new extension. Wall thickness is included in this measurement.

Can I have a flat roof on a permitted development extension?

Yes — flat roofs are acceptable for permitted development extensions. However, no part of the roof should be used as a balcony or raised terrace, and rooflights must not project more than 150mm above the roof surface.

What is the maximum width of a permitted development rear extension?

There is no specific width limit for single-storey rear extensions under Class A, but the extension must not extend beyond the side walls of the original house and must not cover more than 50% of the curtilage. In practice, most rear extensions span the full width of the house’s rear wall.

How do I measure the ‘rear wall of the original dwellinghouse’?

The measurement is taken from the original rear wall of the dwellinghouse — not from any subsequently added extensions. If a 1.5-metre extension was added in 2010, the PD depth limit still runs from the original wall, meaning that extension counts toward your PD allowance. Only 1.5 metres of new depth remains (for a semi-detached house with a 3-metre allowance).

Get a Free Feasibility Check

Crown Architecture & Structural Engineering provides free initial feasibility assessments to confirm whether your extension can proceed under permitted development. We handle LDC applications, building regulations submissions, and full planning applications where required.

Call 07443804841 or complete the form above to speak to an architect.