How Much Does a House Extension Cost in the UK in 2026?
Blueprint UK
6/18/20261 min read
One of the first questions homeowners ask when considering an extension is: "How much is this actually going to cost?" Unfortunately, there is no one-size-fits-all answer, as extension costs vary significantly depending on location, size, specification, and structural complexity.
In 2026, a typical single-storey rear extension in the UK generally costs between £2,000 and £3,500 per square metre, although projects in London and the South East can exceed this range. For many homeowners, a modest rear extension may fall between £35,000 and £80,000, depending on finishes and design requirements.
It is important to remember that construction costs are only part of the overall budget. Many projects also require:
Architectural drawings
Planning Permission or Permitted Development advice
Structural calculations
Building Regulations drawings
Building Control fees
Party Wall matters (where applicable)
One of the biggest mistakes homeowners make is obtaining builder quotes before the design has been properly developed. Without drawings and structural information, builders often have to make assumptions, which can lead to inconsistent or inflated quotations.
A clear design package allows builders to price the same scope of work, giving homeowners more confidence when comparing quotations.
At Blueprint UK, we help homeowners understand the full project journey—from initial feasibility and planning advice through to structural engineering and Building Regulations support—allowing projects to progress with greater certainty and fewer surprises.
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