The best extension isn't the biggest one — it's the one that fixes how your home actually works. Before you settle on a shape, it helps to know what each type of house extension does well, roughly what it costs, and where planning permission comes in. Here's a plain-English guide for homeowners across South West London and Surrey.
Single-storey rear extension
The most common project we build. It pushes the back of the house out into the garden — usually to create an open-plan kitchen-diner with bi-fold or sliding doors and far more natural light. It is the go-to for families who want a bigger, brighter kitchen without losing much garden, and many rear extensions fall under permitted development, so no full planning application is needed. As a guide, budget around £1,900–£2,700 per m² for the finished space (roughly £30,000–£80,000 for a typical single-storey rear), with about 12–18 weeks on site once design and planning are done.
Side-return extension
The classic Victorian and Edwardian terrace transformation. It fills in the narrow, wasted alley beside the kitchen — often only a metre or two wide, but enough to square off the room and pour light in through a glazed roof. It works best where the house is long and thin and the kitchen feels cramped; a structural steel and a rooflight do most of the heavy lifting. Costs usually land at £2,100–£2,900 per m² (about £40,000–£90,000), and like rear extensions, many side-returns are permitted development rather than a full application.
Wrap-around extension
A side-return and a rear extension combined into one L-shaped footprint — the biggest change you can make to the ground floor short of rebuilding. It gives you a single, generous open space for kitchen, dining and living, and it is the right call when you want one seamless floor rather than separate rooms. Expect £2,100–£3,000 per m² and £80,000–£160,000 overall. Because of the scale, a wrap-around usually needs full planning permission rather than permitted development.
Double-storey (two-storey) extension
Going out and up at the same time: extra ground-floor living space with a bedroom, bathroom or study stacked above it. It is often the best value per square metre, because both floors share one set of foundations and one roof — so it suits growing families who need an extra bedroom as much as more room downstairs. Budget around £2,400–£3,400 per m² (£80,000–£170,000). Two-storey extensions almost always need full planning permission, and party-wall agreements with next-door neighbours are common.
Going up: loft conversions and added storeys
If your footprint is tight or you would rather keep the garden, the space you need may be overhead. A loft conversion turns the roof void into a bedroom suite or home office, and on some houses a full extra storey is possible. It follows its own rules and structural design — we cover it properly on our loft conversions page.
Garden rooms, orangeries and outbuildings
Not every extra room has to be attached to the house. A detached garden studio, orangery or outbuilding can give you a home office, gym or annexe — frequently under permitted development, and usually the quickest and most affordable route to a usable room. It is worth considering when the main layout already works and you simply need more space.
Which extension is right for you?
The right choice comes down to three things: the shape and size of your plot, your budget, and how you actually want to live day to day. A growing family opening up the kitchen needs something different from a couple future-proofing with a ground-floor suite. Our free cost calculator gives you an instant price range for each type in about two minutes, and a free on-site visit turns it into a fixed, itemised quote. From the first sketch through planning to handover, one in-house team handles it all — see house extensions for the full picture.
