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 ever going to the planning committee — saving months 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 — written for 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 (which have no PD rights at all), and they carry strict conditions on size, height, position and materials. Break any single condition and the whole project falls outside PD — needing 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 8m 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 added volume	Up to 50m³	Below the ridge line
Outbuilding (garden room)	Max 50% garden coverage	Max 50% garden coverage	2.5m near a boundary

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 — now a permanent scheme — which needs a prior-approval neighbour-consultation process (adjoining neighbours are notified and can object).

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 and outbuildings

• 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, not forward of the front elevation, and covering no more than 50% of the garden.

When permitted development does NOT apply

• Flats and maisonettes — no PD rights whatsoever.
• Conservation areas, listed buildings and AONBs — heavily restricted; listed buildings need 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 is faster and cheaper than a full planning application, and it removes the risk of an enforcement issue later.

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 — 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 have no PD rights at all — every change needs an application.

Frequently Asked Questions