What You Can Build Without Planning Permission

Not every extension needs a planning application. Under permitted development (PD) rights, many London homeowners can extend, convert a loft, or add an outbuilding without making a planning application, saving the 8-week wait for a decision and removing a major source of uncertainty. But PD is narrower and more conditional than most people assume, and getting it wrong can mean an enforcement notice and undoing the work.

Here is where the lines sit in 2026, based on England's householder PD rules. Always confirm the detail for your own property, because the conditions vary by house type, by location, and by whether your council has removed PD rights in your area.

What permitted development actually is

PD rights are a national grant of planning permission from central government, so you can build certain things without applying to your local council. They apply to houses, not flats or maisonettes (flats do not get the householder rights to extend, enlarge the roof or build outbuildings), and they carry strict conditions on size, height, position and materials. Break any single condition and the whole project falls outside PD and needs a full householder planning application instead.

Permitted development limits at a glance

Here is how the main allowances compare by project and house type (England, 2026). Treat these as the standard limits: your specific property, and any Article 4 direction, can change them.

Project	Terraced / Semi	Detached	Max height
Single-storey rear extension	3m deep (up to 6m with prior approval)	4m deep (up to 8m)	4m
Side extension	Max ½ the width of the house	Max ½ the width	4m
Rear dormer loft	Up to 40m³ for a terrace, 50m³ for a semi	Up to 50m³	Below the ridge line
Outbuilding (garden room)	Max 50% garden coverage	Max 50% garden coverage	2.5m within 2m of a boundary; otherwise 4m (dual-pitched roof) or 3m

Single-storey rear extensions

This is the most common PD project. You can build a single-storey rear extension up to:

• 3m deep for a terraced or semi-detached house, or 4m for a detached house, with a maximum height of 4m.
• 6m / 8m respectively under the Larger Home Extension route (a permanent scheme), which needs prior approval from the council: adjoining neighbours are notified and have at least 21 days to object, the fee is £249, and the work may start if the council has not decided within 42 days. The route is not available in conservation areas.

If the extension comes within 2m of a boundary, the eaves cannot exceed 3m, and materials should be similar in appearance to the existing house.

Loft conversions and dormers

A rear dormer usually sits within PD, provided the added roof volume stays under 40m³ (terraced) or 50m³ (semi-detached and detached). The catch most people miss: you cannot add a dormer to the principal (front) elevation facing a road under PD, side-facing windows must be obscure-glazed and non-opening below 1.7m, and the dormer must be set back from the eaves. Mansard conversions almost always need full planning permission.

Side extensions, outbuildings and heat pumps

• Side extensions: single storey only, maximum 4m high, and no wider than half the width of the original house.
• Outbuildings (garden offices, gyms): single storey, maximum 2.5m high within 2m of a boundary (otherwise 4m with a dual-pitched roof or 3m with any other roof), not forward of the principal elevation, and, together with other extensions and buildings, covering no more than 50% of the land around the original house. Our garden room and outbuilding rules guide covers the detail.
• Air source heat pumps: since 29 May 2025 the old rule keeping the unit at least 1m from the boundary no longer applies; the unit can be up to 1.5m³ and must meet the MCS 020(a) noise limit of 37 dB(A). See our heat pump guide for Victorian terraces.

When permitted development does NOT apply

• Flats and maisonettes: no householder PD rights (extensions, roof enlargements, outbuildings).
• Conservation areas, listed buildings and National Landscapes (formerly AONBs): heavily restricted; listed buildings need listed building consent for almost any change.
• Article 4 areas: your council can remove PD rights street by street (common across London's conservation areas). Always check your specific address.
• Anything forward of the principal elevation, or beyond the size limits above.

The smart move: a Lawful Development Certificate

Even when your project clearly is permitted, it is worth applying for a Lawful Development Certificate (LDC) from the council. It is a formal confirmation that no planning permission is needed: invaluable when you come to sell, and protection against any future dispute. It costs £274 for proposed householder works (£136 for an outbuilding alone), half the £548 planning application fee, and it removes the risk of an enforcement issue later.

Certificates are usually granted. Between September 2025 and August 2026, London councils granted 90.6% of lawful development certificates for loft conversions, and in the 24 boroughs where both routes could be measured, 52% of loft conversion decisions were certificates rather than planning applications (our 2026 London planning approvals study).

Common permitted development mistakes

The same handful of errors trip homeowners up again and again, and they are expensive to undo:

• Assuming PD applies in a conservation area. Many rights are removed or reduced; side extensions and cladding almost always need permission.
• Forgetting about Article 4. Councils can strip out PD rights street by street, and your neighbour's project being fine doesn't mean yours is.
• Miscalculating depth or roof volume. A few centimetres over the 3m/4m line, or over the 40m³/50m³ loft volume, takes the whole project outside PD.
• Skipping the Lawful Development Certificate. Without it you have nothing to prove the work was lawful when you sell.
• Treating a flat like a house. Flats and maisonettes do not have householder PD rights, so every extension or external change needs an application.

Frequently Asked Questions