Rear Extension Cost UK
A rear extension is one of the most popular ways to add living space to UK homes — typically £40,000–£80,000 for a standard single-storey build of around 20m², with costs driven by size, glazing, foundation type and regional labour rates. Whether you want a larger kitchen-diner, open-plan living area, or additional reception room, extending to the rear can transform how you use your home without the need to move. For broader project context, see our full house renovation cost guide and our Victorian terrace renovation guide (terraces are the most common property type for rear extensions), and for how regional labour rates shift the budget see the average UK renovation costs by region insight.
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Get Your Free EstimateUK Rear Extension Costs (2026)
Small Single Storey (15m²)
£30,000 - £50,000
Basic kitchen extension
Standard Single Storey (20-25m²)
£45,000 - £75,000
Kitchen-diner extension
Large Single Storey (30m²+)
£60,000 - £100,000
Open-plan living space
Two Storey (40m² total)
£80,000 - £150,000
Kitchen + bedroom above
What Affects Rear Extension Costs?
- Size: Larger extensions cost more overall but less per square metre
- Storeys: Two-storey extensions cost 50-60% more than single storey for double the space
- Foundation type: Standard strip foundations vs piled foundations on poor ground
- Roof design: Flat roofs are cheaper than pitched or lantern roofs
- Glazing: Bi-fold doors and skylights add £3,000-£15,000
- Internal finish: Budget, mid-range, or high-end specification
- Location: London and the South East cost 25-40% more than northern regions
Single vs Two-Storey Rear Extension
A single-storey rear extension is the most common choice, typically used to create a larger kitchen, kitchen-diner, or family room. They are quicker to build, often fall under permitted development, and cause less disruption during construction.
A two-storey rear extension offers better value per square metre, adding both ground floor and first floor space. While more expensive overall (typically £80,000-£150,000), the cost per square metre is lower. They require planning permission in most cases and take longer to build.
Popular Rear Extension Features
Modern rear extensions often include large glazed openings to the garden, typically bi-fold or sliding doors. Roof lanterns and skylights bring natural light deep into the space, while vaulted ceilings create a sense of openness.
Many homeowners combine their rear extension with internal remodelling, removing walls to create open-plan living areas. Underfloor heating is popular in rear extensions, providing comfortable warmth without radiators taking up wall space.
Planning and Building Regulations
Single-storey rear extensions often fall under permitted development, allowing you to build without formal planning permission. However, all extensions require building regulations approval, covering structural safety, insulation, drainage, and electrics. Budget £500-£1,500 for building regulations fees and inspections.
Calculate Your Rear Extension Cost
Every rear extension project is different. Get a personalised estimate based on your property type, location, and requirements using our free renovation calculator.
Enter your details to see realistic cost ranges for your rear extension, then use this as a starting point when obtaining quotes from local builders.
How We Calculate Costs
RenoCost estimates are calculated from published UK cost benchmarks and RenoCost's documented per-module cost assumptions. The model adjusts these assumptions using the property characteristics, selected renovation scope, finish level and broad postcode-based pricing region, then presents a low, mid and high planning range.
- Published UK benchmarks — macro reference points for construction costs and materials and labour trends, used to sense-check RenoCost's own assumptions.
- RenoCost's per-module assumptions — cost and duration assumptions for each renovation module, reviewed and updated periodically by the RenoCost team.
- Estimate ranges — low, mid and high bands set to reflect the realistic spread between competitive and premium specifications, rather than a single fixed price.
Data confidence note
Completed calculator estimates are used to produce anonymous renovation-planning insights. They are not contractor quotations, invoices or confirmed final project costs. RenoCost estimates are intended for initial planning and budgeting. Property condition, specification, access, contractor availability and site-specific requirements can change the final cost. Always obtain detailed written quotations before committing to a project.
Regional adjustments are applied based on postcode area to reflect broad differences in local labour and material rates. See our Method Glossary for definitions of the terms used here.