These are the workhorses of the serious extension market. A double-storey extension adds rooms on two floors for barely more structure than one: bedrooms and bathrooms above, open living below. A wrap-around turns the side return and the rear into one L-shaped space that rebuilds the whole ground floor around light and the garden. The Extension Company designs and builds both across London and Hertfordshire from our Cockfosters base, on fixed-price terms with planning handled end to end.
Which one is your project?
Choose the double-storey when the pressure is bedrooms. Growing families who love the street they are on get the extra bedroom and en-suite upstairs and the kitchen-diner below in one programme, and the cost per square metre beats a single-storey because the roof and foundations are shared across two floors.
Choose the wrap-around when the pressure is the ground floor. Victorian and Edwardian side returns waste exactly the space the kitchen needs; wrapping side and rear together creates the wide, light room those houses were never given.
Choose both, or more, when the house needs rethinking. On premium plots these schemes are often the first move of a bigger programme, extension plus internal remodel, which is whole-house transformation territory and the heart of our luxury extensions service.
What they cost in 2026
Realistic all-in build ranges across our patch, excluding VAT, professional fees and kitchen fit-out:
| Scheme | Typical London cost | Premium postcodes | On-site time |
|---|---|---|---|
| Wrap-around extension | £85,000 to £160,000 | £90,000 to £190,000 | 4 to 6 months |
| Double-storey rear | £90,000 to £190,000 | £95,000 to £240,000 | 5 to 7 months |
| Double-storey + ground-floor remodel | From £150,000 | £250,000 to £500,000 | 6 to 9 months |
Expect £2,800 to £4,200 per square metre as the baseline and £3,500 to £5,500 in the premium postcodes, with the drivers behind the bands unpacked in the luxury extension cost guide. Every quote is fixed and itemised before work starts.
The planning reality
Neither scheme hides under permitted development: double-storey rears and wrap-arounds go to full application, decided in roughly eight weeks and won on design. That is not bad news. It means the difference between approval and refusal is the quality of the scheme, not the luck of the rules, and design is the fight we pick deliberately: massing that respects the neighbours, materials matched to the host house, daylight assessments where overlooking is the officer's worry. On green belt and conservation plots the extra layers join the case, and we build for those constraints from the first sketch. Party wall procedures apply as usual, managed by us, with surveyor costs of £1,000 to £2,500 per affected neighbour where appointed.
Structure you only want to buy once
Two-storey additions carry real engineering: foundations sized for the load, steels that let the ground floor open up, junctions where new roof meets old that must never leak. Our fixed-price build covers the full chain, structural engineer to building control certificate, with one project lead accountable throughout and the programme dates given in writing with the quote.