House Extensions in Bournemouth: Costs, Planning & Timings
House extensions in Bournemouth are one of the jobs we price most often, and the conversation nearly always starts with the same questions. What will it cost? Do we need planning permission from BCP Council? And how long are we going to be living with builders? This guide answers them with current 2026 figures from our own work across Southbourne, Charminster, Moordown, Queens Park and Westbourne.
Bournemouth's housing shapes a lot of the answer. A 1930s semi in Kinson, a Victorian villa near Boscombe and a 1960s bungalow in Throop all extend differently, and the ground under them varies more than most people expect.
How much does a house extension cost in Bournemouth?
We price every extension from a proper site survey, but here's where the numbers sit at south-coast rates as of October 2026. These are our customer prices, taken through to plastered, decorated and ready to use:
Single-storey rear extension, standard spec: £2,300 to £3,250 per m²
A typical 20 m² kitchen-diner extension: £46,000 to £65,000 for the build itself
Two-storey extension: £2,400 to £3,350 per m² of new floor area
What pushes a job towards the top of that range? Usually the glazing (a long run of aluminium sliders or a roof lantern), a steel beam to open up the back of the house, and whatever the ground decides to do. Kitchens, flooring and new heating sit on top, so it's worth deciding early whether those are in our scope or yours. Smaller extensions also cost more per square metre, because the drawings, groundworks set-up and building control don't shrink much with the footprint.
Do you need planning permission for an extension in Bournemouth?
Often you don't. Plenty of single-storey rear extensions go ahead under permitted development, with no full planning application. For a typical house the main limits are:
Single-storey rear: up to 3 m deep on a semi or terrace, 4 m on a detached house, and no more than 4 m high
Within 2 m of a boundary, the eaves can't go above 3 m
Side extensions: single storey only, and no wider than half the original house
Extensions and outbuildings together can't cover more than half the garden
You can go deeper, up to 6 m on a semi or 8 m on a detached house, through the prior approval route. That costs £249 and gives the neighbours a chance to comment. Anything bigger, or a two-storey extension close to a boundary, needs a householder application. The council fee for that is £548, and the target for a decision is eight weeks.
There are catches. Flats and maisonettes have no permitted development rights at all, and parts of town such as Meyrick Park and Talbot Woods or Boscombe Spa are conservation areas, where the rules tighten. Some houses have had their rights removed by a condition on an earlier consent, which we see on newer estates more often than you'd think. Even when you don't need permission, we'd usually suggest a Lawful Development Certificate. It's half the planning fee, so £274, and it gives you proof when you come to sell.
Bournemouth ground conditions, trees and drains
Most of Bournemouth sits on sandy, free-draining ground, which is generally kind to foundations. The complication is trees. The town's pines are everywhere, lots of them carry Tree Preservation Orders, and roots near the footprint can push foundations well past the standard metre deep. That's why our survey looks at what's growing next door as well as in your own garden.
Drains are the other one. Plenty of older Bournemouth terraces have a shared sewer running across the back gardens, right where an extension wants to go. If yours does, you'll need a build-over agreement with Wessex Water before we start, and we've written up how build-over agreements work if you want the detail. We CCTV the drains while we're planning the job, so nobody gets a surprise once the digger's on site.
How long does a house extension take in Bournemouth?
On site, a single-storey extension usually takes 10 to 16 weeks from groundworks to decoration. A two-storey job is closer to 16 to 24 weeks. Before that there's the lead-in: drawings and structural calculations, planning or prior approval if it's needed, and a building regulations application, with an inspector visiting at each key stage of the build.
Realistically, if you call us this autumn with nothing drawn yet, you're looking at a spring start. That isn't a bad thing. Groundworks go in on drier ground and the shell is up by early summer. Glazing is the one that catches people out, as aluminium doors and roof lanterns are made to order, so we get them on order as soon as the openings are confirmed.
What you get when we build your extension
We run the whole job ourselves, from foundations and steelwork through to the electrics, plumbing and underfloor heating, so you're not trying to line up separate trades and work out whose fault a delay is. You get one point of contact, a fixed written quote after the survey, full insurance, and the building control completion certificate in your hands at the end. It's how we approach all our extensions and general building work across Dorset and Hampshire, and it's why so much of our Bournemouth work comes from neighbours who watched the last one go up.
Related reading
Planning an extension in Bournemouth?
If you're weighing up a rear or side extension anywhere in Bournemouth, Poole or Christchurch, book a site survey with Complete Builds. We'll come out, measure up, check where you stand on planning and give you a fixed price in writing.
Comments