Adding an extension is one of the best ways to get more from your home, but do I actually need planning permission? Some extensions do, and some do not. Many fall under what is called permitted development, meaning you can build without a full planning application, as long as you stay within the limits. Others need planning permission before the project starts.
What is the difference between Planning permission and permitted development?
Planning permission is formal consent from your local council to carry out building work. You submit an application, the council considers the impact on the area and your neighbours, and it grants or refuses permission.
Permitted development is different. It is a set of rights, granted nationally, that lets you make certain changes to a house without applying for planning permission, provided the work stays inside defined size and design limits. Work outside those boundaries in any way and the permitted development right falls away, meaning you then need a full application.
Permitted development applies to houses, not to flats or maisonettes, which always need permission for an extension. And the limits are measured against the “original house”, meaning the house as it was first built, or as it stood in 1948 if it is older. If a previous owner already added an extension, that is included in what you have left to extend.
What usually counts as permitted development?
Single-storey rear extensions
- A detached house can extend up to 4 metres beyond the original rear wall. A semi-detached or terraced house can extend up to 3 metres.
- The extension cannot be more than 4 metres high.
- If it comes within 2 metres of a boundary, the height at the eaves cannot be more than 3 metres.
Side extensions
- A side extension can only be a single storey, with a maximum height of 4 metres.
- It can be no wider than half the width of the original house.
Two-storey and rear extensions above one level
- A rear extension of more than one storey cannot extend more than 3 metres beyond the original rear wall, and cannot come within 7 metres of the rear boundary.
- The roof pitch should match the existing house as closely as possible, and any new upper-floor windows on the side elevation must be obscure-glazed and fixed shut below 1.7 metres.
The rules that apply to every extension
- The extension cannot be higher than the highest part of the existing roof, and the eaves cannot be higher than the existing eaves.
- No more than half the land around the original house can be covered by extensions and outbuildings combined.
- Nothing can extend forward of the principal elevation, in other words the front of the house facing a road.
- Materials should be similar in appearance to the existing house.
The larger home extension scheme
There is a middle route between permitted development and a full planning application, called the larger home extension scheme. It lets you go further out at the back without applying for planning permission in the usual sense, through a lighter process known as prior approval.
Under this scheme, a detached house can build a single-storey rear extension of up to 8 metres, and a semi-detached or terraced house up to 6 metres. You still notify the council, and it carries out a neighbour consultation: your immediate neighbours are told about the plans and given the chance to comment. If none object on the grounds of impact, the work can go ahead. It is a lighter touch than a full application, but it is not automatic, and it does not apply everywhere, as the next section explains.
When you will need full planning permission
You will need to apply for planning permission if your extension does any of the following: extends forward of the front of the house, goes beyond the size limits above, covers more than half the surrounding land, or sits on a property that has had its permitted development rights removed. Flats and maisonettes always need permission.
The local exceptions: National Landscapes, conservation areas and listed buildings
This is where a lot of Herefordshire and Gloucestershire homeowners are caught out, as much of the county is marked as protected land.
On what planning calls designated land, which includes National Landscapes (the new name for Areas of Outstanding Natural Beauty, and the reason the Wye Valley and the Cotswolds have tighter rules), conservation areas, National Parks and World Heritage Sites, several permitted development rights are switched off. Side extensions and two-storey rear extensions are not permitted development on this land and need planning permission. The larger home extension scheme does not apply here either. Cladding the outside of the house is also ruled out. In short, if you live in the Wye Valley or Cotswolds National Landscapes, assume you have less freedom than the national limits suggest, and check before you plan.
Alongside planning permission, most work to a listed building needs separate listed building consent, and the design has to be sympathetic to the character of the original structure. This is specialist ground, and getting it wrong carries real consequences, so it is always worth taking advice early.
An Article 4 direction, common in conservation areas, withdraws specific rights for a street or area. And newer homes on housing estates often have permitted development removed by a planning condition when the estate was approved. Your council can confirm whether either applies to your property.
Even without planning permission, Building Regulations still apply
Planning permission and Building Regulations are two separate things. Even when your extension is permitted development and needs no planning application, the structural work still has to meet Building Regulations, covering foundations, structure, insulation, drainage, fire safety and more. That approval is a given on any extension we build, and we manage it on your behalf, so it is never something you have to chase.
How to be certain before you build
You can apply to the council for a Lawful Development Certificate, which formally confirms that your extension is permitted development and does not need planning permission. It is well worth having: it protects you if the position is ever questioned, and it reassures a future buyer’s solicitor when you come to sell.
Through our design and planning service, we assess the likely route for your extension at the very start, prepare the drawings, and handle the planning application or prior approval from beginning to end. We have worked with conservation officers at both Herefordshire Council and Cheltenham Borough Council, and we will tell you honestly what is achievable before any application goes in. You deal with one team from the first site visit through to handover, with no guesswork about permissions along the way.
If you are weighing up an extension and want a clear answer on whether you will need planning permission, get in touch. We are always happy to talk it through before you commit to anything.
Frequently Asked Questions
Do I need planning permission for a single-storey rear extension?
Often not. A single-storey rear extension is usually permitted development if it stays within the size limits: up to 4 metres beyond the original rear wall for a detached house, or 3 metres for a semi-detached or terraced house, and no more than 4 metres high. Go beyond those depths and you will need either the larger home extension scheme or full planning permission. On protected land such as the Wye Valley or Cotswolds National Landscapes, check first, as the allowances are tighter.
How big can I build an extension without planning permission?
It depends on your house type and where you extend. As a rough guide, a detached house can add a single-storey rear extension of up to 4 metres under permitted development, or up to 8 metres through the larger home extension scheme with neighbour consultation. Semi-detached and terraced houses can go to 3 metres, or 6 metres under the scheme. Side extensions are limited to single storey and half the width of the house. The safest way to be sure is to have the limits checked against your specific property.
Do the rules change in the Wye Valley or the Cotswolds?
Yes. Both are National Landscapes, formerly known as Areas of Outstanding Natural Beauty, which counts as designated land. Side extensions and two-storey rear extensions are not permitted development there and need planning permission, the larger home extension scheme does not apply, and external cladding is not allowed. If your home is in one of these areas, assume you have less freedom than the national limits suggest and take advice before you plan.
Do I still need Building Regulations approval if I do not need planning permission?
Yes. Planning permission and Building Regulations are separate. Even a permitted development extension has to meet Building Regulations for its structure, foundations, insulation, drainage and safety. We manage this approval on every extension we build, so it is handled for you.
How long does planning permission take?
Councils aim to decide most householder applications within about eight weeks of validating them, though this can vary with the workload of the local authority and the details of your scheme. We set out the likely timeline for your project before work begins, so you always know what to expect at each stage.
Thinking about an extension?
We will tell you honestly whether your project needs planning permission before you commit to anything.
