House Extensions

As a realistic starting point, all ex VAT and indicative: on typical London jobs priced on our estimator in October 2026, a single storey rear extension of about 20 m² of new floor, flat roofed with no rooflights, plus making good the room it joins, came to around £57,000, roughly £2,900 per square metre of new floor, and our minimum for a complete project, once finishes and fittings are included, is around £85,000, because even a small extension carries almost the same baseline of work as a larger one. A two storey side return adding around 48 m² of new floor area came to around £128,000. Pairing a 20 m² extension with a full refurbishment of a 130 m² house came to between £165,000 and £195,000. For new above ground space at a standard specification, £2,650 to £2,900 per square metre of new floor is a realistic inner London range before professional fees. These figures price windows, doors, any rooflights, sanitaryware and tiles for fitting only, with the products supplied by you, and leave out kitchen units, worktops and appliances. The rest depends on size, design, specification and the condition of the existing property, which is why the instant estimator prices yours from your own description and sends a realistic range to your inbox in minutes.

Most London houses extend in one of five ways, and the right one depends on the plot, the light and how you want the ground floor to work:

• A rear extension: the simplest way to add a larger kitchen and family room across the back of the house. See rear extensions in London.
• A side return: filling the narrow passage beside a terrace's back addition, which widens the kitchen. Our guide to rear extension or side return compares the two.
• A wraparound: the side return and the rear together, one L-shaped room. See wraparound extension ideas.
• A two storey extension: new space on both floors, usually cheaper per square metre. See two storey extension costs.
• A glazed extension: more light, with more care over heat and glare. See our glass extensions guide.

Not always. In England, as of October 2026, many single storey rear extensions are permitted development: up to 3 metres beyond the original rear wall of a terraced or semi detached house, or 4 metres for a detached house, and no more than 4 metres high. Larger rear extensions, up to 6 metres or 8 metres for a detached house, can go through the prior approval route, in which the council consults the neighbours before deciding. Side extensions under permitted development are single storey, no more than 4 metres high and no wider than half the original house. In a conservation area, on a listed building or for a flat, the rules are tighter and an application is usually needed. We check the position for your street, prepare the drawings and manage the application where one is needed. Building regulations approval applies either way, and party wall notices where the work is on or near a shared wall.

At St Germans Place in Blackheath we built a rear basement extension, and at Milford Mews in Streatham a double storey extension with an open plan living room lit from two aspects.

We deliver house extensions as a complete design and build service in London, from first concept and planning through construction to final finishes, so one team is accountable for the whole project.