Permitted development, explained
What permitted development covers, the limits that catch people out, and how to prove afterwards that you stayed within them.
Permitted development rights let you build certain things without a full planning application. Here's what that covers, and the limits worth knowing before you design.
Permitted development can save you weeks of waiting and a layer of cost, which is why it is worth understanding properly. It is also widely misread, and the mistakes tend to surface at the worst possible moment, usually when you come to sell.
What permitted development actually is
Permitted development is a national grant of planning permission, given by legislation rather than by your local council. It allows specified works within specified limits, so if your project stays inside them you can build without applying.
Two things are worth understanding straight away. It is a right, not an approval, so no paperwork is issued by default. And it can be taken away locally, by an Article 4 direction or by a condition attached to an earlier permission on your property.
The main household allowances
Each type of work has its own dimensions and conditions. These are the ones most homes rely on.
- Single-storey rear extensions: 3m on terraced and semi-detached houses, 4m on detached, within a 4m height cap
- Larger rear extensions: 6m and 8m respectively, through the prior approval route rather than automatically
- Loft conversions: 40 cubic metres on terraced houses, 50 cubic metres on other houses, keeping the roof shape
- Outbuildings and garden rooms: single storey, 2.5m maximum overall height within 2m of a boundary
- Porches: up to 3 square metres, 3m high, and at least 2m from any highway
Prior approval: the middle route
Between doing nothing and a full application sits prior approval, which covers larger single-storey rear extensions. You notify the council, they consult your immediate neighbours, and if no objection is upheld the work can proceed.
It is not a full planning application and it is not automatic either. Most people have never heard of it, which is why larger rear extensions are often assumed to be impossible when they are not.
The limits that catch people out
Refusals and enforcement cases rarely come from the headline dimensions. They come from the conditions attached to them.
- Allowances are measured against the original house, so earlier extensions may already have used yours
- Outbuildings must not cover more than half the land around the original house
- Side extensions are limited to half the width of the original house
- Materials should match the existing house, and side-facing upper windows must be obscure glazed
- Nothing may project forward of the principal elevation facing a highway
Where rights disappear entirely
Flats and maisonettes have no permitted development rights at all. Listed buildings need consent for work that would otherwise be permitted. Conservation areas, national parks and areas of outstanding natural beauty have reduced rights, and many newer estates carry planning conditions that remove them.
An Article 4 direction can also withdraw rights street by street, which is why a neighbour's completed extension is never proof that yours is allowed.
Proving it afterwards
Because there is no application, there is no decision notice to keep. A lawful development certificate fills that gap: a formal confirmation from the council that the work was permitted development.
It is optional, but a buyer's solicitor will ask how the work was authorised, and an unanswered question at that point costs far more than the certificate would have.
Where we come in
We confirm which route applies to your property in writing, free, prepare the drawings, and handle the application with the council. See extension drawings, or get your drawings quoted with no obligation. If any application we submit is refused, you get a 100% refund within 5 days.
Your planning route, the real limits, and the mistakes that get extensions refused.