Extension prices in South London sit noticeably above the national average, and Croydon is no exception. Most homeowners here should budget somewhere between £2,200 and £3,500 per square metre for the build itself, before fees and VAT. Here is an honest breakdown of what that means for a real project on a real street.
For a straightforward single storey rear extension on a Croydon terrace or semi, a sensible working range is £2,200 to £3,000 per square metre for a standard finish. That puts a typical 4m x 5m rear extension at roughly £44,000 to £60,000 for the build, with kitchens, glazing upgrades and professional fees on top.
Double storey extensions work out cheaper per square metre because the roof and foundations are shared across two floors, often £1,900 to £2,600 per square metre. Side return infills, common on Victorian terraces around areas like South Norwood and Thornton Heath, tend to cost more per square metre than their size suggests because access is tight and there is a lot of structural steel relative to the floor area gained.
The single biggest variable is specification. A basic finish with standard bifolds, painted plasterboard and a mid range kitchen sits at the bottom of the ranges above. Structural glazing, underfloor heating, flat roof lanterns and flush thresholds can add 20 to 40 percent without changing the footprint at all.
Ground conditions matter more in Croydon than many people expect. Parts of the borough sit on clay with significant tree coverage, which can mean deeper foundations than the standard one metre trench. If a build over agreement is needed because you are within three metres of a Thames Water public sewer, which is common on rear extensions, allow extra time and a few hundred to a few thousand pounds depending on whether it needs a formal approved agreement.
Build cost is not project cost. Architectural drawings and structural engineering for a typical rear extension usually come to £3,000 to £7,000. A householder planning application to Croydon Council currently costs a few hundred pounds, though many rear extensions fall under permitted development, where a lawful development certificate is a worthwhile safeguard. Building control fees typically add £700 to £1,200.
VAT at 20 percent applies to most extension work carried out by a VAT registered builder, and it is worth checking whether quotes include it. Finally, hold a contingency of at least 10 percent. On older Croydon housing stock, the unknowns behind the walls and under the floors are where budgets usually slip, not the headline quote.
Ask each builder to price against the same set of drawings and a written specification, otherwise you are comparing guesses. A quote that is dramatically cheaper than the others usually excludes something: check whether it covers making good, decoration, electrics certification, and connection of the new space to your existing heating.
A staged payment schedule tied to completed work, rather than large sums up front, is standard practice with reputable local builders. It is also reasonable to ask for addresses of recent extensions in the borough and to speak to those homeowners directly. Croydon has plenty of similar housing stock, so a builder who has worked on your street type before will price more accurately and surprise you less.
Many single storey rear extensions fall under permitted development, meaning no full planning application is needed, though limits on depth and height apply and flats and maisonettes are excluded. A lawful development certificate from Croydon Council is a sensible way to prove the work was legal when you sell.
A single storey rear extension usually takes 10 to 14 weeks on site, while a double storey or wrap around can run 16 to 24 weeks. Add two to four months beforehand for design, approvals and party wall matters.
In much of the borough, added floor space is valued at more than the typical build cost per square metre, so a well built extension usually adds value as well as space. That said, returns vary street by street, so it is worth checking local sold prices for extended versus unextended equivalents before committing.
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