Permitted Development Extension Rules 2027: How Big Can You Build?

Permitted development extension limits (England)

These rules apply to England under the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended), Schedule 2, Part 1, Class A. Scotland, Wales and Northern Ireland have different systems. Always check your local planning authority and any Article 4 direction before you dig foundations.

For a single-storey rear permitted development extension, the Planning Portal and GOV.UK technical guidance still use these depth limits measured from the rear wall of the original house:

Figures above are the current Planning Portal / GPDO position as of November 2026. “Original house” means the house as first built, or as it stood on 1 July 1948 if built earlier. A previous owner’s extension counts against your remaining depth.

Single-storey rear extensions within the 3 m / 4 m band are not subject to the neighbour consultation scheme. Once you go beyond those depths (but stay within 6 m / 8 m), you must use larger home extension prior approval before works start.

Larger home extension prior approval

Prior approval for a larger home extension applies only to single-storey rear extensions that extend beyond the original rear wall by:

• Detached: over 4 metres and up to 8 metres.
• Any other house: over 3 metres and up to 6 metres.

It is not available on Article 2(3) land (conservation areas, National Parks, the Broads, AONBs, World Heritage Sites and certain other designated areas) or on Sites of Special Scientific Interest. In those places the larger 6 m / 8 m route does not apply — you fall back to the tighter limits or full planning permission.

1. Notify the council before work starts. Apply online via the Planning Portal for “Prior Approval: Larger Home Extension”. You cannot do this retrospectively.
2. Include the required details. Written description with rear projection, eaves height and overall height; a site plan; addresses of adjoining premises; and the fee.
3. Neighbours are consulted. If an adjoining owner or occupier objects, the council decides whether the impact on amenity is acceptable.
4. Wait for the trigger to start. Do not start until the council confirms prior approval is not required, grants prior approval, or 42 days pass without a decision on a valid application.

Even with prior approval, the extension must still meet every other Class A condition (height, materials, side-width rules, and so on). The council can refuse if the proposal is outside permitted development.

Do I need planning permission for an extension?

You usually need a full householder planning application if any of the following apply:

• Depth beyond PD. Rear projection past 4 m (detached) or 3 m (other) without a valid larger-extension prior approval route, or past 8 m / 6 m in any case.
• Two-storey rear. Two-storey rear extensions have tighter Class A limits (including a 3 metre rear depth in many cases) and often need planning permission on constrained plots.
• Side extensions on protected land. Side additions facing a highway, or wrapping side-and-rear “infill” that breaks width or depth tests.
• Flats, listed buildings, Article 4. Householder PD does not cover flats. Listed buildings need listed building consent. Article 4 directions can remove PD rights street by street.
• Front elevations and principal elevations. Extensions that go beyond a wall forming a principal or side elevation fronting a highway are tightly restricted.

If you are unsure, apply for a Lawful Development Certificate (proposed). It is optional but useful for buyers and lenders. Building Regulations are separate from planning and still apply to almost every extension.

Height, width and other Class A limits

Depth is only one test. A permitted development extension must also stay within other Class A limits, including:

• Height. Single-storey enlargements under the rear rules must not exceed 4 metres in height.
• Eaves and ridge relative to the house. The extension must not be higher than the highest part of the existing house roof, and eaves rules apply where the extension comes within 2 metres of a boundary.
• Side width. Where a side extension is involved, total width must not exceed more than half the width of the original house.
• Materials. Exterior materials should be of similar appearance to the existing house (with limited exceptions such as conservatories).
• Garden coverage. Enlarged parts plus outbuildings must leave enough of the curtilage undeveloped — Class A uses a “more than half the area of the curtilage” test against the original house footprint.

Wrap-around side-and-rear extensions must satisfy both rear and side tests at once. That is a common reason “designs that look like PD” still need planning permission.

Worked example: semi-detached rear extension

What is not current law

From time to time, government consultations and press coverage float bigger permitted development depths or new householder rights. Unless the change appears in the GPDO on legislation.gov.uk and is reflected in Planning Portal / GOV.UK guidance, treat it as a proposal, not something you can build under today.

As of November 2026, the live Planning Portal guidance still shows the familiar 3 m / 4 m standard rear limits and 6 m / 8 m larger rear extensions with prior approval. Do not assume a bigger limit is already in force because a minister announced an intention or a draft Order was discussed.

Once you know the lawful footprint, size materials and budget with the Home Extension Calculator. For kitchen-specific pricing, see our kitchen extension cost guide; for roof-space alternatives, compare loft conversion types.

Certificates and next steps

A Lawful Development Certificate (proposed) is not mandatory, but it is often worth the fee when you plan to sell or remortgage soon after building. Buyers’ solicitors routinely ask how a deep rear extension was authorised. Prior approval decision notices and Building Control completion certificates should live with your deeds pack.

Sequence the project like this:

1. Measure from the original rear wall and list any existing extensions.
2. Check designations — conservation area, listed status, Article 4, SSSI, national park.
3. Pick the route — standard PD, larger home extension prior approval, or full planning.
4. Appoint design and structural input before you demolish.
5. Submit Building Regulations (building notice or full plans) in parallel with planning where needed.

If your goal is an open-plan kitchen, confirm services moves and boiler position while the planning route is still flexible. Depth that is lawful on paper can still be a poor buy if it leaves a useless strip of garden or fails daylight rules on a neighbour’s window — prior approval exists partly to surface those amenity fights early.

Frequently Asked Questions

Sources

• Planning Portal — Prior approval for extensions — Confirms 3m/4m standard and 6m/8m larger rear extension prior approval thresholds.
• GOV.UK — Permitted development rights for householders: technical guidance — Class A rear depth, height and neighbour consultation rules for England.
• Planning Portal — Larger Home Extension guidance note (PDF) — Process, definitions of original house and Article 2(3) land.
• legislation.gov.uk — GPDO 2015 Schedule 2 Part 1 — Statutory Class A permitted development conditions.

When you are ready to estimate materials or cost for your project, open the Home Extension Calculator and enter your measurements.