The larger home extension route: going deeper without a full application
There is a middle path between permitted development and a full planning application. It lets a single-storey rear extension go to 8m on a detached house, or 6m on anything else — provided the neighbours get their say first.
What it actually is
Ordinary permitted development caps a single-storey rear extension at 4m deep on a detached house and 3m on a semi or terrace. The larger home extension scheme doubles both, to 8m and 6m. It was introduced as a temporary measure in 2013 and made permanent in 2019, and it is still one of the least-known routes in householder planning.
It isn't planning permission. You're still building under permitted development — you just have to tell the council first and let them consult your neighbours. Councils call this prior approval, and the process has a nickname that describes it better: the neighbour consultation scheme.
The catch is in that word, consultation. You are handing your neighbours a formal opportunity to object, on a timetable, in writing. Most don't. But the ones who do can stop the extension at 4m or 3m, and there is no appeal against a neighbour simply disagreeing with you.
The limits you still have to meet
Depth is the only thing the scheme relaxes. Everything else in Class A still applies, and getting one of them wrong voids the whole thing:
| Condition | Detached | Semi, terrace, end-terrace |
|---|---|---|
| Maximum depth from the original rear wall | 8m | 6m |
| Maximum height overall | 4m | |
| Maximum eaves height within 2m of a boundary | 3m | |
| Storeys | Single storey only | |
| Designated land (conservation area, National Park, AONB, World Heritage Site) | Scheme not available | |
“Original” means the house as first built, or as it stood in July 1948 if that's earlier — not as you bought it. A previous owner's extension eats into your allowance, and people are caught by this more often than by any of the numbers above.
How the process runs
You submit a prior approval application with a written description, a plan of the site and drawings showing the extension and the neighbouring properties. There's a fee, well below a full householder application — the Planning Portal's fee calculator has the current figure, and it changes.
The council then writes to the adjoining owners and occupiers. They get 21 days. If nobody objects within that window, the council confirms and you can build. If somebody does object, the council has to consider whether the impact on the neighbour's amenity is acceptable, and decide either way.
The whole thing is meant to take 42 days. Start to finish, budget six to eight weeks before you can put a spade in the ground, and don't order materials against the earlier date.
One practical point that catches people: you cannot start work before the council responds, even if the 42 days run out. Building anyway makes the extension unauthorised, and no amount of arguing about deadlines fixes that.
When it's worth it, and when it isn't
The scheme earns its keep on a terrace or semi where 3m gets you an awkward galley and 6m gets you a room. That extra 3m is often the difference between an extension that changes how the house works and one that just makes the kitchen slightly less cramped.
It's worth less than people expect on a detached house with a long garden, because 4m already buys a usable space and going to 8m starts to eat lawn you'll miss. And it's worth nothing at all if you're on designated land, where the scheme simply doesn't apply and a full application is the only route.
Cost scales roughly with floor area, and the model puts a single-storey extension at an indicative £24,928 to £50,200 across 519 UK towns — BestBuilders' 2026 regional cost model, not quotes we hold. Going from 3m to 6m on a typical 4m-wide return roughly doubles the footprint, so plan for the upper half of that range. The detailed per-metre breakdown lives on BestBuilders' extension cost page, which is a sister site of ours.
Frequently asked
Where the rules come from
The scheme sits in Class A of Part 1, Schedule 2 of the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended. The Planning Portal's householder pages and the government's technical guidance on permitted development for householders both set out the conditions in plainer English than the Order does. Everything on this page is England only — Scotland, Wales and Northern Ireland each run their own permitted development regimes and the figures differ.
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