Home extension costs have risen again in 2026, driven mainly by three things: tighter building regulations, higher labour costs, and an increase in the planning application fee. For a typical single-storey extension, this has added a few thousand pounds to the overall budget compared with last year. Want to see what your own project might cost with today’s figures? Try our instant extension estimator for a ballpark price in under a minute.

What’s actually changed since last year

Building regulations got tighter. New Part L building regulations came into effect and now set stricter requirements for insulation, air-tightness and ventilation in any new extension. Walls, roofs, floors, windows and doors all need to perform to a higher standard than before. This is a good thing for your energy bills long term, but it adds real cost to the build, typically somewhere between £3,000 and £8,000 depending on the size and design of the extension. If a builder’s quote looks suspiciously low, it’s worth checking whether they’ve actually priced in current Part L compliance or left it out to win the job.

Labour costs are up. Skilled tradespeople, particularly bricklayers and carpenters, remain in short supply across the country. Labour rates have risen roughly 7 to 11 percent year on year in 2026, and that’s before you factor in regional demand. Extensions are a labour-heavy job, so this has a direct knock-on effect on the final bill.

Planning fees have gone up too. From April 2026, a standard householder planning application in England costs £548, up from £528 the year before. It’s a relatively small increase in the context of a whole project, but it’s one more line that’s crept up.

Material costs remain high. Prices haven’t spiked the way they did a few years ago, but they’ve stayed well above pre-2020 levels and continue to edge upward. Timber, insulation and glazing in particular have not come back down.

What this means in real terms

Put together, these changes mean a typical single-storey extension now costs somewhere in the region of £1,800 to £3,000 per square metre across the UK, with the exact figure depending heavily on location, size and specification. In Nottinghamshire and the wider East Midlands, that tends to sit at the lower to middle end of the national range, usually £1,800 to £2,600 per square metre, which is one of the reasons this part of the country still offers reasonable value compared with London or the South East.

For a 20m² extension, a common size for an open-plan kitchen-diner, that works out at roughly £40,000 to £55,000 including VAT once you factor in current regulations and labour rates. A year or two ago, the same project would likely have landed a few thousand pounds lower.

Curious what your own numbers look like? Our instant extension estimator is built around current 2026 pricing, so you can set your extension type and dimensions and see a realistic range straight away, rather than working from an out-of-date average.

Why some quotes still look cheaper than others

If you’re comparing quotes and one comes in noticeably lower than the rest, it’s worth asking exactly what’s included. The most common reasons for a big gap are:

  • Part L compliance left out or under-specified. Some builders quote to an older, cheaper standard and leave the extra insulation or glazing costs as a surprise later.
  • Preliminaries missing. Scaffolding, skip hire, site welfare and project management are sometimes left off a rough quote and added afterwards.
  • No contingency. A sensible contingency of 10 to 15 percent covers things like drains that need diverting or ground conditions that weren’t visible until digging started. If a quote has no room for the unexpected, the final bill often ends up higher than the number you were originally given.
  • Basic specification as standard. Budget bricks, uPVC windows and a flat roof will always come in cheaper per square metre than matching brick, aluminium glazing and a proper roof structure. That’s not dishonest, but it should be made clear upfront.

A fixed price, agreed in writing before work starts and based on a proper specification, is the best protection against costs creeping up once the build is underway.

Is it still worth extending in 2026?

For most homeowners, yes. Even with costs having risen, extending remains cheaper than moving in most cases once you factor in stamp duty, estate agent fees and the cost of finding a new property in the current market. A well-planned extension, particularly one that adds an open-plan kitchen-diner or extra bedroom, continues to add meaningful value to a property, and the higher insulation standards now required mean the space will also be cheaper to run for years to come.

The key in 2026 is going in with realistic expectations from the start. A ballpark figure based on this year’s actual costs, not a number from an old guide or a builder’s memory of a job from three years ago, gives you a far more useful starting point for budgeting.

Get a realistic figure for your project

If you’re planning an extension in Nottinghamshire, South Yorkshire or Derbyshire and want a number based on current 2026 pricing rather than guesswork, the quickest way is to try it yourself.

Try the Instant Extension Estimator →

Set your extension type and size, see a live price range built on today’s costs, and get in touch when you’re ready for an accurate quote from Rosebrick Developments.