Can I build an extension without planning permission?
Many single-storey extensions are permitted development — within strict size and height limits. The basis is the GPDO 2015 (Class A). A single-storey rear extension can be up to 3m deep on an attached house or 4m on a detached one, with a maximum height of 4m. The Larger Home Extension route allows up to 6m (attached) or 8m (detached), but only via a prior-approval notification with a 42-day neighbour consultation — you must wait for the decision. Within 2m of a boundary, eaves are capped at 3m. Side extensions can be single-storey, up to 4m high and half the width of the house. You can't build forward of the principal elevation facing a highway, can't exceed the existing ridge, and extensions plus outbuildings can't cover more than 50% of the garden. Building Regs always apply. In short: yes within the limits, or via prior approval for bigger.
📋 The rules
- Single-storey rear: 3m attached / 4m detached, max 4m high
- Larger Home Extension: 6m/8m via prior approval (42-day notice)
- Eaves max 3m within 2m of a boundary
- Not forward of the principal (highway) elevation
- Extensions + outbuildings: max 50% of the garden
🔓 Exceptions
- No permitted development for flats or maisonettes
- Designated land: no side extensions; the 6m/8m scheme is unavailable
- Article 4 directions or planning conditions can remove PD
⚠️ Penalties & fines
If you need full permission, the England householder fee is £548; the Larger Home Extension notification is about £120, and a Lawful Development Certificate is around £274. Building without the permission you needed can lead to a refused retrospective application and an enforcement notice (a criminal offence to ignore, unlimited fine), within the 10-year enforcement window. Beware a myth: "anyone can build a 6m or 8m extension without telling the council" is false — that's only possible via the prior-approval scheme with a 42-day neighbour consultation; building first risks enforcement. And remember permitted development never removes Building Regs. (Scotland and Wales use their own permitted-development metrics and have no 6m/8m neighbour scheme.) Before building: check the depth, height and 50% limits, use the prior-approval route for larger extensions, and book Building Control.
📎 Official sources
- GOV.UK — planning permission →
- Planning Portal — extensions permitted development →
- GPDO 2015 — Schedule 2, Part 1 →
❓ Frequently asked
How big an extension can I build without permission?
A single-storey rear extension can be up to 3 metres deep on a terraced or semi-detached house, or 4 metres on a detached one, with a maximum height of 4 metres, as permitted development. Larger rear extensions of up to 6 or 8 metres are possible, but only through the Larger Home Extension prior-approval route with neighbour consultation.
What is the Larger Home Extension scheme?
It's a permanent prior-approval route that lets you build a single-storey rear extension up to 6 metres deep on an attached house, or 8 metres on a detached one. You must notify the council, which consults your neighbours for 42 days. If no neighbour objects, or the council approves, you can proceed; you can't simply build first.
Can I extend the front of my house?
Generally not under permitted development. You can't build an extension forward of the principal elevation that fronts a highway without planning permission. Permitted development is aimed at rear and, in limited cases, side extensions. A porch has its own separate, smaller permitted-development allowance, but a full front extension needs an application.
Is there a limit on how much of my garden I can build on?
Yes. Extensions, together with any outbuildings, must not cover more than 50% of the area of land around the original house, as it stood in 1948 or when first built. This 50% curtilage rule is a key permitted-development limit, so large or multiple structures can quickly use up your allowance.
Do extensions need Building Regulations?
Yes, always. Whether or not your extension needs planning permission, it will need Building Regulations approval covering structure, foundations, insulation, drainage, fire safety and more. Building Control should be involved from the start, and a completion certificate is important when you come to sell or remortgage the property.
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