How much does a home extension cost in 2026? – Price per m² guide

What does an extension cost per m²?

Simple single-storey extension without wet rooms, such as an extra bedroom or living area: often around EUR 2,200–3,000 per m² in Western Europe.

Extension with a kitchen or bathroom: often around EUR 3,000–4,000 per m², because plumbing, drainage and electrics add significant cost.

Second-storey or loft extension: often EUR 3,000–4,500 per m² or more, depending on how much of the structure and roof must be rebuilt.

Costs differ greatly between countries. A 25 m² extension in Western Europe often lands between EUR 55,000 and 100,000.

Why small extensions cost more per m²

Foundation, roof, the connection to the existing house and design cost almost the same whether you build 15 or 30 m², so the price per square metre falls as the extension grows.

Removing part of the existing wall, moving services and adapting the roofline are often extra.

Permits and fees

Most extensions need planning permission or a building permit; smaller ones may be allowed under local permitted-development rules. Always check with your municipality.

Permits, structural engineering, inspections and design belong to the client costs (K1) and are often 10–20% on top of construction.

Common pitfalls

Forgetting that existing heating, electrics and ventilation may need upgrading.

Underestimating groundwork – rock, clay or a sloping site affects the foundation.

Comparing quotes that do not cover the same scope, such as finishes, painting or windows.

Estimate your extension

Our calculator covers 11+ countries and five currencies. Choose renovation/extension, enter area, standard, location and ground conditions to get a breakdown per building part and K1/K2, VAT shown separately and a PDF report.