Planning Permission for House Extensions in North London: Permitted Development Explained

Most single-storey extensions to houses in England do not need a planning application. They are "permitted development" under the Town and Country Planning (General Permitted Development) (England) Order 2015, provided they stay within limits on depth, height, width and coverage, and provided the house is not a flat, is not in a restricted area and has not already used its allowance. Everything else — wraparounds, most double-storey schemes, anything on designated land that goes beyond the basic limits — needs a householder planning application, which costs £258 and takes eight weeks to decide. This guide sets out the rules as they stand in September 2026 and how the North London councils apply them.

Permitted development limits for extensions (Class A)

"Original house" means the house as first built, or as it stood on 1 July 1948 if built before then. Every previous extension — including one built by a previous owner — counts against the allowance, which is why we check the planning history of a property before advising. The Planning Portal's extensions guidance is the authoritative summary; the Order itself is Schedule 2, Part 1, Class A.

The larger home extension scheme (prior approval)

If a single-storey rear extension needs to be deeper than 3 m (or 4 m on a detached house), up to 6 m (8 m) is possible without a full application through prior approval. You notify the council with a plan and description; the council writes to adjoining neighbours, who have 21 days to object; if nobody objects, the council confirms within 42 days that prior approval is not required and you may proceed. If a neighbour objects, the council decides whether the extension's effect on their amenity is acceptable. The fee is £120. The scheme does not apply on designated land (conservation areas, AONBs, National Parks) and does not override Article 4 directions.

When you need a planning application

• Wraparound extensions. Rear and side extensions cannot be joined under permitted development, so an L-shaped scheme needs an application.
• Most double-storey extensions. Two-storey side extensions are never PD; two-storey rear extensions only within tight limits (3 m, 7 m to the boundary), which rules out most North London gardens.
• Anything on a flat or maisonette. No PD rights; the freeholder's consent is usually needed too.
• Designated land beyond the basic limits. On conservation-area land, side extensions, two-storey rear extensions and cladding need permission.
• Article 4 areas. Where a council has made an Article 4 direction, the rights it names are removed and an application is required for those works.
• Listed buildings. Planning permission and listed building consent, including for many internal works.
• Where a previous extension has used the allowance.

A householder application costs £258 in England (from 1 April 2025) and must be decided within eight weeks of validation unless you agree an extension of time. The council consults neighbours for 21 days and assesses the scheme against its local plan, its residential design guidance and, in conservation areas, the character appraisal. Refusals can be appealed to the Planning Inspectorate, but it is far cheaper to design an approvable scheme first.

How the North London councils apply the rules

Barnet

Barnet has 16 conservation areas, including Hampstead Garden Suburb, Totteridge, Mill Hill and Monken Hadley, ten of which carry Article 4 directions. Outside them, Barnet's 1930s housing stock retains full PD rights and rear extensions, hip-to-gable lofts and rear dormers are routine. Barnet's residential design guidance expects side extensions to be set back and subordinate, and applies the 45-degree daylight test to rear extensions next to neighbours' windows. In Hampstead Garden Suburb, the HGS Trust's consent is needed in addition to planning permission.

Harrow

Harrow's residential design guide is specific: single-storey rear extensions generally accepted; side extensions set back from the front and subordinate; two-storey side extensions keeping around 1 m to the boundary at first floor to avoid a terracing effect. Thirty conservation areas — Harrow on the Hill, Pinner High Street, Stanmore Hill among them — and several Article 4 directions bring external alterations under control.

Haringey and Camden (Highgate, Muswell Hill, Crouch End)

Large conservation areas with Article 4 directions cover most of the period housing. Side-return and modest rear extensions are commonly approved on application; large dormers and front-facing changes are resisted. Camden has an additional basement policy requiring impact assessments. Decision times are often longer than the statutory eight weeks; plan for it.

Enfield

Generally receptive to rear extensions and rear dormers on semis outside its conservation areas (Enfield Town, Winchmore Hill Green, Grange Park, Bush Hill Park, The Lakes Estate, Southgate Green), where Article 4 directions cover many front-facing changes.

Hertsmere (Radlett, Bushey, Elstree, Borehamwood)

Outside the Radlett and Bushey conservation areas houses retain PD rights. Hertsmere has Article 4 directions on several groups of Radlett bungalows and Bushey streets, and applies green belt policy to the village edges: extensions must be proportionate to the original house, measured as a percentage increase, and replacement dwellings must not be materially larger.

Building Regulations are separate — and always required

Planning permission (or the lack of need for it) says nothing about whether the extension is safely built. Every extension needs Building Regulations approval covering foundations, structure, insulation, glazing, drainage, ventilation, electrics and fire safety, inspected at stages by the council's building control or an approved inspector. We submit full plans with the structural engineer's calculations before starting so nothing is built on an assumption.

Party walls are separate too

If the extension is built up to or on the boundary, if steels bear on a shared wall, or if you excavate within 3 m of a neighbour's foundations, the Party Wall etc. Act 1996 requires written notice — one month for a new wall at the boundary or for excavation, two months for work to an existing party wall — before work starts. Neighbours who dissent, or who do not respond within 14 days, trigger surveyors and a party wall award. It is not a planning matter and the council will not check it, which is why it is so often forgotten until the week before work starts.

Get a Lawful Development Certificate even if you don't need permission

A scheme can be permitted development and still cause trouble later if you cannot prove it. A Lawful Development Certificate (£129, up to eight weeks) is the council's formal confirmation that the extension was lawful. Solicitors ask for it when you sell; lenders ask for it when you remortgage; neighbours cannot reopen the question. We apply for one on every PD extension we build.

What we do

At the first site visit we establish the planning route — PD, prior approval or application — from the property's history, its designation and the brief, and we design to that route so approvals come first time. See house extensions and architectural design and planning, or read about the risks of building without permission.