Planning guide · England & Wales
Most single-storey rear extensions can be built under permitted development — no full planning application needed. But the limits are easy to trip over, and they differ between England and Wales. Here is how it works, and how we get yours drawn and approved at a fixed price.
Often, no. A large share of single-storey rear extensions are classed as permitted development — a national grant of planning permission that lets you build within set limits without a full application. Whether yours qualifies depends on its size, your property type and where you live.
You are likely to need a full planning application if your extension goes beyond the permitted-development limits below, if your home is a flat or maisonette (these usually have permitted development removed), or if your property sits on designated land — a conservation area, national park or Area of Outstanding Natural Beauty — or is subject to an Article 4 Direction that withdraws permitted development rights. Listed buildings need separate consent on top.
The single biggest mistake homeowners make is mixing up the England and Wales rules — they are set by different legislation. Here is how single-storey rear extensions are treated in each.
We are an online architectural design service — the practical alternative to a traditional high-street architect. Our qualified design team draws your plans, works out whether you are permitted development or need a full application, and deals with the council on your behalf.
Not always. Many single-storey rear extensions fall under permitted development and can be built without a full planning application, provided they stay within set size and design limits. You are more likely to need full planning permission if the extension is large, is on a flat, sits on designated land such as a conservation area, or your home has an Article 4 Direction.
In England, a single-storey rear extension can reach up to 3m beyond the original rear wall (terraced or semi-detached) or 4m (detached) as standard, doubling to 6m and 8m under the Larger Home Extension prior-approval route. Overall height is capped at 4m. Wales uses its own order — broadly similar standard depths, but different rules for larger extensions — so the exact limit depends on your property and authority.
In England, larger single-storey rear extensions (beyond the standard 3m or 4m, up to 6m or 8m) are allowed under permitted development but must go through prior approval. The council notifies your adjoining neighbours, who have 21 days to object on amenity grounds. It is lighter than a full application, but must be applied for before any work begins.
Yes. Planning rules govern whether you can build; building regulations govern how — structure, insulation, drainage, fire safety and ventilation. Almost every rear extension needs building regulations approval, whether or not it needed planning permission.
We strongly recommend it. Even when your extension is permitted development, a Lawful Development Certificate from your council is formal proof the work was lawful — which makes selling your home far smoother, as buyers and solicitors often ask for it.
With Arkiplan, drawings are typically ready in three to six weeks after your design call. A prior-approval or full planning decision usually takes around eight weeks from a valid submission, though this varies by council.
No call required, no card required — just a tight, fixed-price range tailored to your project, with the planning route confirmed for your address.
This guide is general information, not planning advice, and permitted development rules change and depend on your specific property and local authority. We confirm the current position for your address as part of every project.