Extension Price 2025 – What You’ll Actually Pay
Thinking about adding a sunroom, a garden room or a full‑blown house extension this year? You’ve probably asked yourself, “How much will it cost?” The answer isn’t a simple £10,000‑£20,000 box. It depends on size, materials, location, planning rules and the kind of builder you hire. Below we break down the biggest cost drivers and give you practical ways to keep the price from blowing out.
Key Drivers of Extension Price in 2025
First off, size matters. A 15 m² lean‑to will cost far less than a 45 m² two‑storey addition. In 2025 the average price per square metre for a standard brick‑and‑block extension sits around £1,800‑£2,200, but premium finishes like timber frames or glass walls can push that to £3,000‑£3,500.
Materials are the second big factor. Traditional brick is still the cheapest, while engineered timber, insulated panels, or high‑performance glazing add 15‑30 % to the total. Don’t forget the roof – a pitched roof with slate costs more than a flat roof with felt.
Location plays a role too. Building in London, the South East or coastal areas often means higher labour rates and transport costs for bricks and timber. Rural sites can be cheaper, but you might pay more for site access or for bringing in utilities.
Planning permission or permitted development rights also affect price. If your project stays within the permitted development limits, you save on fees and design time. Anything that requires a full planning application adds architect fees, survey costs and possibly a longer timeline, which can increase finance charges.
How to Keep Your Extension Budget on Track
Start with a clear brief. Sketch out exactly what you need – number of rooms, ceiling height, heating type – before you talk to a builder. The more precise you are, the fewer change orders later, which are the biggest budget killers.
Get at least three quotes and ask each builder to break down the estimate into labour, materials, site work and contingency. Compare line items, not just the total. A lower quote may hide higher material costs or an under‑scoped project.
Consider off‑site construction where possible. Prefabricated wall panels or modular garden rooms can shave weeks off the build and reduce waste, which translates into lower labour costs.
Allocate a 10‑15 % contingency for unexpected issues – like hidden damp or ground movement. Most extensions stay within this range if you’ve done a thorough site survey up front.
Finally, think about the long‑term savings. A well‑insulated extension with double‑glazed windows will cost more now but lower heating bills for years to come. Factor those savings into your ROI calculation.
Bottom line: In 2025 a typical five‑room, 30 m² extension will land between £55,000 and £70,000 for a standard build, but can rise to £90,000‑£110,000 for premium finishes or complex rooflines. By controlling size, material choices and getting detailed quotes you can keep the project within your comfort zone and avoid nasty surprises.
Ready to start planning? Grab a notebook, write down your must‑haves, and schedule a few site visits. Knowing the numbers up front makes the whole process less stressful and more rewarding.
