How Much Does an Extension Cost in the UK (2024)?
Building an extension is one of the most effective ways to add value and space to your property, but budgeting accurately is critical. A standard 30sqm single-story extension outside of London will typically start from £55,000 to £70,000+ depending on the level of finish.
Single Storey vs Double Storey
A common misconception is that a two-story extension will cost double the price of a single-story. It doesn't.
The most expensive elements of an extension are the foundations and the roof. Because a two-story extension uses the same foundation footprint and the same roof size as a single-story extension, the cost per square metre is usually cheaper on the second floor. Our calculator automatically adjusts the rate per square metre based on the storey you select.
Basic vs Premium Finish
- Basic (£1,500 - £1,800/m²): Plastered walls, standard radiators, uPVC windows, basic lighting, DIY decorating.
- Standard (£2,000 - £2,400/m²): Mid-range kitchens/bathrooms, bifold doors, underfloor heating, finished flooring.
- Premium (£2,500 - £3,000+/m²): High-end custom glazing (e.g., roof lanterns, oversized sliders), smart home integrations, premium hardwood flooring, luxury bespoke kitchens.
Don't Forget About VAT
When receiving quotes from builders, strictly clarify whether they are quoting inclusive or exclusive of VAT. 20% is a huge sum on a build project. Our calculator explicitly breaks out the 20% VAT element so you aren't hit with unexpected surprises.
The Contingency Fund
As seen in the calculator results, we always calculate a 10% contingency into your maximum range. Groundworks can reveal unexpected pipes. Soil types might require deeper trenches. You might decide you prefer the more expensive tiles midway through the build. Always secure a contingency fund before breaking ground.