How much does a house extension cost in Derby? (2026)

Typical extension costs in Derby

A single-storey rear extension of around 20–25 sq metres — the most common type — generally costs £28,000 to £45,000 in Derby fully finished, including foundations, structure, glazing, and plastering. That works out at roughly £1,400 to £1,800 per square metre, which is a fair benchmark for the East Midlands.

A double-storey extension adds a bedroom or bathroom above the ground floor and costs more per square metre because the structural and roofing work is proportionally larger. Expect £55,000 to £90,000 for a decent double-storey job in Derby. Side-return extensions, wraparounds, and basement conversions all carry higher costs again — basements in particular can reach £150,000 or more once waterproofing, tanking, and underpinning are factored in.

These figures assume a standard brick-and-block build with a pitched or flat roof. Timber frame, steel frame, or heavily glazed designs — such as a garden room or orangery — will push costs up by 15 to 30 per cent. Fitting out the new space (kitchen, en suite, flooring) is always on top of the build cost and should be budgeted separately.

What affects the price

Ground conditions are one of the biggest variables. Derby has areas of made ground, old mine workings, and clay soils that can all require deeper foundations or specialist engineering. If your builder quotes without a soil survey and the ground turns out to be problematic, you can face five-figure overruns. A basic trial pit survey costs £300 to £600 and is worth every penny.

The existing house matters too. Extending a semi-detached typically means a party wall agreement with your neighbour, which adds £700 to £1,500 in surveyor fees. Listed buildings or properties in conservation areas may need planning permission where permitted development rights would otherwise apply, and the design restrictions that come with listed consent add cost.

Labour rates vary more than most homeowners expect. A sole trader with low overheads will quote less than a well-established building firm with a site manager, but that does not automatically mean better value. A credible contractor will provide a detailed written quote, a clear payment schedule, and evidence of public liability insurance. Be cautious of anyone asking for more than 10 to 15 per cent upfront before any work starts on site.

How to get an accurate quote and avoid overpaying

Get at least three quotes from builders who have actually visited the site. Phone estimates are not quotes. A proper quote should itemise groundworks, structure, roof, windows and doors, internal finishes, and VAT — which is charged at 20 per cent on most extension work. If a quote is presented as a single lump sum with no breakdown, ask for the detail before you accept it.

Agree everything in writing before work starts: the scope, the payment schedule, who supplies materials, what happens if unexpected issues arise, and the expected completion date. A simple contract protects both sides. The Federation of Master Builders has a free contract template that is a good starting point. Never pay the final tranche until you are satisfied the snagging list has been addressed.

Posting your job on Rank My Builder puts it in front of verified tradespeople local to Derby whose reviews you can read before you pick up the phone. Jobs are capped at five quotes, so you get a shortlist of genuine interest rather than a flood of calls from firms who are too busy to take you seriously.

FAQs