Prior approval: the larger home extension (6m and 8m) rule

The larger home extension scheme lets you build a single-storey rear extension deeper than standard permitted development allows — up to 6 metres on a terraced or semi-detached house, and up to 8 metres on a detached one — without a full planning application. It is one of the most useful permitted-development rights for London homeowners. It is also one of the most misunderstood, because it is not "no permission needed": it is a prior-approval process, with a neighbour consultation built in, and missing a step can cost you the right to use it at all.

This page explains exactly how the larger home extension works, the limits that apply, the neighbour-consultation mechanics and timescales, why it can never be retrospective, and how it differs from the separate prior-approval route for adding a storey on top.

The limits

• Single-storey rear extension only — it does not cover side returns, two-storey extensions or wrap-arounds.
• Up to 6m beyond the original rear wall for a terraced or semi-detached house; up to 8m for a detached house. ("Original" means as the house was built, or as it stood in 1948 — not as you bought it.)
• Maximum height 4m overall, and no higher than the eaves of the existing house. Where the extension is within 2m of a boundary, the eaves height is limited to 3m.
• It must not extend beyond a side elevation, and together with other extensions must not cover more than half the area of land around the original house.
• Not available on designated land — conservation areas, national parks, Areas of Outstanding Natural Beauty and World Heritage Sites are excluded, and the right does not apply to flats, maisonettes or listed buildings.

How the prior-approval process runs

• You apply to the council for prior approval, describing the extension and its dimensions, with a plan and the addresses of adjoining properties. As at 2026 the prior-approval fee for a larger home extension is £249 (from 1 April 2026) — planning fees re-index every 1 April, so confirm the current figure on the Planning Portal fee calculator.
• The council notifies the owners and occupiers of adjoining properties — the neighbour consultation scheme — giving them a minimum of 21 days to object on the grounds of impact on their amenity (light, outlook, overbearing effect).
• If no adjoining neighbour objects, the council cannot refuse on amenity grounds and prior approval is effectively granted. If there are objections, the council assesses the impact on neighbours' amenity and decides whether to grant prior approval.
• The council must determine the application within 42 days of a valid submission. If they don't notify you of a decision within that period, you may proceed — but get written confirmation of the deemed approval before building.

Larger home extension vs adding a storey

People often lump "prior approval" together, but the larger home extension (a deeper single-storey rear extension) is a different right from the upward-extension route introduced in 2020, which allows additional storeys on certain houses. The upward-extension right (Class AA) has its own, stricter prior-approval process covering external appearance, neighbours' amenity, natural light to existing windows and the impact on the street — and far more conditions. If you're thinking about going up rather than back, that's a separate route with a separate set of tests.

When the larger home extension is the wrong tool

• Your home is in a conservation area or is listed — the right doesn't apply; you need full planning permission (and, if listed, listed building consent).
• An Article 4 direction has removed the right on your street — common across inner London. The Planning Permission Checker area check flags this.
• Your property is a flat or maisonette — permitted development doesn't apply to flats at all.
• You want a side return, a wrap-around or a two-storey extension — none of these are covered; the larger home extension is single-storey rear only.

How this connects to your Planning Permission Checker report

Whether the larger home extension is even available at your address turns on the designations the Planning Permission Checker report checks — conservation area, Article 4 direction and listed status — against official planning.data.gov.uk geometry. If the report shows your street is clear, the larger home extension may be a genuine route; if it flags a designation, assume a full application. For feasibility and to prepare the prior-approval submission, enquiries route to Hampstead Chartered Surveyors, an RICS-regulated practice (Firm Reg. 923064).