How Much Does a Home Extension Cost in 2026?
The cost of a home extension in the UK varies significantly based on size, location, and specification. On average, expect to pay between £1,800 and £2,500 per square metre for a single-storey extension, with London and the South East typically 20-35% higher than the national average.
Key Cost Factors
- Location: Labour costs vary by up to 40% across UK regions
- Size: Larger extensions benefit from economies of scale
- Specification: Standard vs premium finishes can double costs
- Structural work: Opening up to existing rooms adds complexity
- Glazing: Bi-fold doors and roof lanterns are popular but premium priced
Average Extension Costs (2026)
Small single storey (15m²)
£30,000 - £45,000
Medium single storey (25m²)
£50,000 - £75,000
Large single storey (40m²)
£80,000 - £120,000
Double storey (40m² per floor)
£120,000 - £180,000
Loft conversion (dormer)
£40,000 - £60,000
Extension Cost by Region
Location is one of the biggest factors affecting extension costs. Labour rates, material delivery costs, and local demand all vary across the UK. London and the South East command the highest prices, while regions like the North East and Wales tend to be the most affordable.
Our calculator automatically adjusts costs based on your postcode, using up-to-date regional multipliers derived from trade labour rates and local material pricing. This ensures your estimate reflects real costs in your area rather than a generic national average.
Regional Price Multipliers (vs National Average)
London
+25% to +35%
South East
+15% to +20%
South West & East of England
+5% to +10%
Midlands & North West
Average
North East & Yorkshire
-5% to -10%
Wales & Scotland
-5% to -15%
What Affects Extension Costs?
Beyond location and size, several factors can significantly influence the final cost of your home extension. Understanding these helps you make informed decisions about where to invest and where to save.
Extension type and storey count are the primary cost drivers. A double-storey extension costs roughly 50-60% more than a single storey of the same footprint, not double, because the foundations and roof are shared. Wraparound extensions that combine rear and side elements offer excellent value per square metre due to shared structural walls.
Construction method matters too. Traditional brick and block remains the most common choice, but timber frame construction can be 5-10% cheaper and faster to erect. Structural insulated panels (SIPs) offer superior insulation but at a premium price.
Specification and finishes can swing costs dramatically. A standard kitchen extension with vinyl flooring and basic units might cost £1,800/m², while the same space with underfloor heating, bi-fold doors, a roof lantern, and a high-end kitchen could reach £3,000/m² or more.
Planning permission and building regulations add both cost and time. If your extension falls within Permitted Development rights, you'll save on planning fees and potentially months of waiting. Building regulations approval is always required and typically costs £500-£1,500 depending on the project size and your local authority.
Site access and conditions can catch homeowners off guard. Restricted access for deliveries, sloping ground, poor soil requiring deeper foundations, or the need to reroute drains and services can all add £2,000-£10,000 to the budget.
How Our Calculator Works
Our extension cost calculator combines three data sources to produce accurate, personalised estimates. First, we use current UK trade rates for labour. Bricklayers, electricians, plumbers, plasterers, and other trades, updated quarterly from industry surveys and builder feedback.
Second, we apply regional pricing multipliers based on your postcode. These account for the well-documented variation in labour costs and material delivery charges across different parts of the UK. A £50,000 extension in Manchester might cost £65,000 in London due to these regional differences.
Third, wherever possible we use live material pricing from major UK builders' merchants. This means your estimate reflects actual current prices for bricks, blocks, timber, insulation, roofing materials, and other key items rather than outdated averages. You can see how these prices have been moving on our UK material price trends page. As you answer each question, the calculator refines the estimate in real-time. You can see costs update as you make choices about specification, finishes, and features.
UK Building Material Price Trends
Building material prices are currently trending up, with an overall increase of 38.7% over the past six months. We track 255 materials across 10 categories, with 4 trending down, 6 trending up, and 0 stable.
These price movements directly affect extension costs. Our calculator uses live pricing data to ensure your estimate reflects current market conditions.
Frequently Asked Questions
Common questions about home extension costs, planning, and how to save money on your build.
Builders typically mark up materials by 15-25% to cover their time sourcing and managing supplies, trade account administration, delivery coordination, and the risk of wastage or damage on site. This markup also compensates for their expertise in selecting the right materials and their trade relationships that can secure better availability. By self-managing your build and sourcing materials directly, you can avoid this markup entirely - which is why our calculator shows both self-managed and contractor pricing.
A single-storey extension typically costs £1,800-£2,500 per square metre in the UK. A 20m² kitchen extension might cost £40,000-£60,000, while a 40m² double-storey extension could cost £120,000-£180,000. Costs vary significantly by location, with London 25-35% higher than national averages. Our calculator adjusts for your specific region using live regional pricing data.
Single-storey rear extensions with flat roofs are typically the most cost-effective option, starting from around £1,800 per m². Using timber frame construction can reduce costs by 5-10% compared to traditional brick and block. Minimising structural alterations to the existing house (such as avoiding removing load-bearing walls) also keeps costs down. A simple 15m² rear extension can cost as little as £30,000.
Yes, self-sourcing materials can save 15-25% on material costs compared to having a builder supply them. Our calculator shows both self-managed and contractor pricing so you can see the difference. By comparing prices across multiple suppliers using PriceNailer, you can find the best deals on building materials and potentially save thousands on your extension project.
Many single-storey rear extensions qualify as Permitted Development and do not need planning permission, provided they meet size limits (3m for attached houses, 4m for detached, or 6m/8m under prior approval). Double-storey extensions almost always require planning permission. You’ll also need Building Regulations approval regardless of whether planning permission is needed. Check with your local planning authority for specific requirements.
A typical single-storey extension takes 8-12 weeks to build once work begins. Larger or double-storey extensions may take 12-16 weeks. Add 8-12 weeks beforehand for planning permission (if needed) and building regulations approval. Our calculator provides a project timeline breakdown showing each construction phase and estimated duration.
Kitchen extensions typically add the most value, often recouping 50-70% of their cost in added property value. Additional bedrooms and bathrooms are also strong value-adders. Open-plan living spaces with bi-fold doors, quality finishes, and good natural light (via skylights or roof lanterns) enhance both value and liveability. The key is ensuring the extension is proportionate to the property and neighbourhood.
Our calculator uses current UK trade rates, regional labour multipliers, and live material pricing data from major suppliers. Estimates are typically within 10-20% of actual costs for standard builds. Accuracy increases as you answer more questions (shown by the confidence percentage). For the most accurate estimate, we recommend getting 3 quotes from local builders and comparing them against our breakdown.
Related Calculators
Planning the finer details of your extension? Use our specialist material calculators to get accurate quantities and costs.