Building Costs per Square Metre in London 2026

Introduction

Understanding building costs per square metre is the starting point for budgeting any residential construction project in London. Costs have risen substantially over the past decade — driven by labour shortages, material price inflation, and the increasingly high specification expectations of London homeowners — and vary significantly by project type, specification level and contractor quality. This guide provides a realistic framework for cost per square metre in London for 2026, based on market data from north London residential projects.

What Does Cost per Square Metre Include?

Building cost per square metre (£/sqm) is typically quoted as a construction cost — meaning it includes contractor's preliminaries, materials, labour, sub-contractor works, and the main contractor's overhead and profit. It does not include:

• Professional fees (architect, structural engineer, M&E consultant, quantity surveyor) — typically 12–18% of construction cost
• Planning application fees and disbursements
• Building Regulations fees
• Fit-out and furniture (where not in the contractor's scope)
• Value Added Tax (VAT) — currently 20%, though some residential work may be zero-rated or reduced-rated
• Party wall surveyor costs
• Contingency (typically 10–15% of construction cost)

Single-Storey Rear Extension

A typical single-storey rear extension of 25–40 sqm in north London at mid specification costs £70,000–£140,000 in construction cost before fees and VAT. The relatively high cost per sqm for smaller extensions reflects the significant fixed preliminary costs (site setup, scaffolding, temporary works, connections) that are proportionally higher for a small project.

Two-Storey Extension

Two-storey extensions achieve a lower cost per sqm than single-storey because the fixed preliminary and structural costs (foundations, scaffold, connections) are spread over more floor area.

Loft Conversion

Basement Extension

Basement construction costs significantly more per sqm than above-ground construction due to excavation, temporary works, waterproofing, underpinning, and the complexity of basement engineering. Total costs for a typical single-level basement under a north London terrace house (40–80 sqm) range from £140,000–£480,000+ in construction cost.

New-Build Residential

Full House Refurbishment

Factors Affecting Cost in North London

The following factors drive costs above or below the typical ranges:

• Access constraints: Properties on narrow streets with limited vehicle access, restricted scaffold zones, or basement excavation without rear access add preliminary cost
• Ground conditions: London clay, underground services, old basements, contaminated ground, and high water tables all add cost
• Conservation area and listed building requirements: Materials restrictions and the requirement for specialist craftsmen add cost in conservation areas
• Existing building condition: Unexpected structural defects, asbestos, lead pipes and other legacy issues add cost in renovation projects
• Market conditions: Contractor demand relative to supply affects tender prices — in a busy market, prices are higher than in a quiet market

Conclusion

Building cost per square metre is a useful planning tool but not a substitute for a detailed cost plan prepared by a quantity surveyor for a specific project. For north London residential projects in 2026, construction costs at mid-to-high specification are substantially higher than national averages — London labour costs, higher material transport costs, and the complexity of inner-city construction all contribute. Engaging a quantity surveyor to prepare an elemental cost plan at RIBA Stage 3 (before the tender stage) provides the most reliable basis for budget management. See the professional fees guide for a complete picture of the costs involved in a residential project beyond construction.