Extension Cost UK 2026: Complete Pricing Guide for Every Type of Home Extension

A home extension is one of the most significant investments a homeowner can make — and in 2026, it's also one of the most expensive. After years of material price inflation, persistent labour shortages, and rising energy efficiency requirements, extension costs across the UK have reached new highs.

But the range is enormous. A modest single-storey rear extension can cost as little as £28,000. A large double-storey side and rear wrap-around with a high-end specification can exceed £200,000. Getting your budget right from the start is the difference between a project that runs smoothly and one that stalls halfway through.

This guide is based on real project data from Page Building Consultants — estimates we've produced for homeowners and contractors across the UK in the past 12 months. Use it to set a realistic budget before you commit to anything.

Extension Cost UK 2026: Quick Reference by Type

These are indicative cost ranges for a standard mid-range specification, excluding VAT and professional fees. Costs assume a typical 3–4 bedroom house in the Midlands or North of England. London and South East add 20–35%.

• Single-storey rear extension (3m x 4m): £28,000–£48,000
• Single-storey rear extension (4m x 6m): £45,000–£75,000
• Double-storey rear extension: £65,000–£110,000
• Single-storey side extension: £30,000–£55,000
• Double-storey side extension: £60,000–£100,000
• Wrap-around extension (side + rear): £80,000–£140,000
• Basement extension: £120,000–£250,000+
• Garage conversion: £15,000–£35,000
• Orangery or garden room: £25,000–£70,000

What's Included in an Extension Cost?

A professional extension quote should be fully itemised. If a contractor gives you a single lump sum without a breakdown, that's a red flag. Here's what a complete extension cost should cover:

• Groundworks and foundations — excavation, concrete, drainage connections
• Structural frame — blockwork, steelwork, timber frame as required
• External walls — brick, block, render, or cladding to match existing
• Roof structure and covering — flat roof, pitched roof, or glass roof lantern
• External windows and doors — bifold, sliding, or French doors; Velux if applicable
• Internal structural alterations — removing walls, installing RSJ steels
• First fix — electrical, plumbing, underfloor heating pipework
• Insulation — walls, floor, and roof to current Building Regulations standards
• Plastering and internal finishes
• Second fix — sockets, switches, radiators or UFH manifold, sanitaryware
• Flooring — typically an allowance for tiles or engineered wood
• Decoration — walls and ceilings
• External works — making good patio, garden, and drainage

What's Driving Extension Costs Up in 2026?

Extension costs have risen significantly since 2021–2023, and while the rate of increase has slowed, prices remain above the long-term average. Here are the key factors pushing costs higher in 2026:

• Labour costs: Skilled trades remain in short supply, keeping wages elevated
• Timber and structural materials: Prices have stabilised after the 2021–2022 spike
• Insulation and energy efficiency materials: Demand remains high due to building regulations changes
• Groundworks: Fuel and plant costs remain elevated
• M&E (mechanical and electrical): Heat pump and EV charging installations adding cost to new builds

Getting an Accurate Cost for Your Project

Cost per square metre figures are useful for initial feasibility, but they're no substitute for a project-specific estimate. The actual cost of your extension will depend on the specific design, site conditions, specification, and programme.

Page Building Consultants produces detailed extension cost plans and bills of quantities for developers, self-builders, and housing associations across the UK. We can typically turn around an indicative cost plan within 24 hours of receiving your drawings.

Call us on 0800 688 9321 or submit your plans online to get a fast, accurate estimate for your extension project.