Construction Cost Benchmarker

The cost to build a house in the UK in 2025 ranges from approximately £1,400 to £3,200 per square metre depending on quality, location and specification. A standard three-bedroom detached house of 120m² in the Midlands would cost roughly £216,000 for construction alone, excluding land and professional fees. London prices are typically 30% higher than the national average.

A standard quality extension in the UK costs approximately £1,600 per square metre in 2025. This ranges from £1,200/m² for basic finishes to £3,000/m² for luxury specifications. These rates include all building works but exclude planning fees, architectural drawings and VAT if applicable. Single-storey rear extensions are generally at the lower end while double-storey extensions offer better value per square metre.

Construction costs vary significantly by region. London is the most expensive at roughly 30% above the Midlands baseline. The South East is around 15% above, while the North East and Wales are approximately 10% below. Northern Ireland tends to be the most affordable region at around 15% below average. These differences reflect local labour rates, material transport costs and market demand.

A per square metre rate typically includes all building works: foundations, structural shell, roofing, internal walls, plumbing, electrical first and second fix, plastering, joinery, decoration and external works. It generally excludes land purchase, stamp duty, architectural and engineering fees, planning application costs, building control fees, VAT (if applicable), kitchen appliances and loose furniture.

Loft conversions in 2025 cost between £1,000 and £2,800 per square metre depending on quality and complexity. A typical dormer loft conversion of 30m² at standard quality costs around £42,000. Velux conversions are cheapest as they require minimal structural changes. Hip-to-gable and mansard conversions are more expensive due to extensive roof modifications but add more usable floor space.

Yes, garage conversions are significantly cheaper than extensions because the shell structure already exists. Basic garage conversions start from around £600/m² compared to £1,200/m² for a basic extension. A single garage conversion typically costs £10,000 to £20,000 while providing 15-18m² of living space. They usually do not require planning permission under permitted development rights.

Online construction cost calculators provide indicative budget estimates, typically within a 15-20% range of actual costs. They use average benchmark rates and cannot account for specific site conditions, ground conditions, access constraints, material choices or local contractor availability. For accurate budgeting, obtain at least three detailed quotes from local contractors after preparing full architectural drawings and specifications.

Industry best practice is to allow 10-15% of the total construction cost as contingency. For renovation and refurbishment projects, 15-20% is advisable because unforeseen issues are more likely when working with existing structures. New builds on straightforward sites can often manage with 10%. The contingency covers unexpected ground conditions, design changes, material price increases and weather delays.

A standard new build house of 120-150m² typically takes 6-9 months from foundation to handover. Extensions usually take 3-5 months, loft conversions 6-10 weeks, and garage conversions 3-4 weeks. These timelines assume no significant delays from weather, material shortages or planning issues. The pre-construction phase including design, planning permission and building regulations adds 3-6 months.

New build residential properties are zero-rated for VAT, meaning you can reclaim VAT on materials and contractor labour through HMRC's DIY Housebuilders Scheme. Renovations and extensions to existing properties are subject to the standard 20% VAT rate. Conversions of non-residential buildings to dwellings may qualify for a reduced 5% VAT rate. Always check your specific circumstances with HMRC or a tax advisor.