Side Return Extension London: Complete Cost Guide 2026
Transform your narrow side passage into valuable living space. Everything you need to know about side return extensions in London for 2026, from costs to planning requirements.
Key Takeaways (2026)
- Average cost: £60,000-£95,000 for a typical London side return extension
- Typical size: 1.2m wide by 3-5m deep, adding 10-15m² of space
- Most require planning permission due to London narrow plots
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What Is a Side Return Extension?
A side return extension fills in the narrow passage that runs along the side of terraced and semi-detached houses in London. This typically unused space - often just 1-1.5m wide - can be transformed into valuable living area, usually to create a larger kitchen or open-plan living space.
Side returns are one of the most popular extensions in London because they maximize the footprint of narrow Victorian and Edwardian terraced properties without extending far into the garden.
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Get Free EstimateAverage Costs in London (2026)
Side return extensions cost between £60,000 and £95,000 for most London properties in 2026. Prices have risen approximately 3-4% from 2025 due to labour cost inflation.
| Quality Level | Cost per m² (2026) | Total (12m²) |
|---|---|---|
| Budget | £3,800-£4,800 | £46,000-£58,000 |
| Mid-Range | £4,800-£5,800 | £58,000-£70,000 |
| High-End | £5,800-£7,500 | £70,000-£90,000 |
| Premium | £7,500+ | £90,000+ |
Note: These figures assume a typical single-storey side return extension of approximately 12m² (1.2m wide x 4m deep x 3m high). Costs can vary significantly based on access, structural work required, and finishes.
Detailed Cost Breakdown (2026)
Typical 12m² Side Return Extension
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The Reality for London Properties
While side extensions can theoretically be built under permitted development, most London terraced houses require planning permission because:
- PD requires the extension to be at least 7m from the opposite boundary
- Most London terraced properties are only 5-6m wide total
- Conservation areas remove PD rights for side extensions entirely
- Many boroughs have Article 4 directions restricting side extensions
Good news: Side return extensions are generally viewed favorably by London planning authorities and have high approval rates (typically 85-90%) when properly designed.
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Check PD Rights (Free)Return on Investment (2026)
Side return extensions typically add more value than they cost in London. Here is what you can expect:
The improved kitchen and open-plan layout are highly desirable features that estate agents consistently report as top buyer priorities in London.
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Frequently Asked Questions
Do I need planning permission for a side return extension?
Most London terraced houses do need planning permission because the side passage is typically less than 7m from the opposite boundary. Conservation areas and Article 4 directions also remove permitted development rights. Use our free PD checker to confirm your specific situation.
How long does a side return extension take to build?
8-12 weeks for construction once you have approvals. Add 2-4 months for planning permission and 2 months for Party Wall process. Total timeline from start to finish: 6-9 months.
Can I combine a side return with a rear extension?
Yes, this is very common and called an L-shaped or wrap-around extension. It maximizes both width and depth for a large open-plan space. Expect costs of £90,000-£145,000 for combined side return and rear extension in 2026 (depending on size and finishes).
Will a side return add value to my home?
Yes, typically £55,000-£90,000 in added value for London properties in 2026, often exceeding the construction cost. The improved kitchen and open-plan layout are highly desirable features for buyers. ROI is generally 120-150% in high-demand areas.
Do I need to move out during construction?
Not usually. Most families stay in place with a temporary kitchen setup. You will lose use of your kitchen for 2-4 weeks during the connection phase. Expect dust and noise, especially when breaking through existing walls. Good builders will contain dust with heavy-duty plastic barriers.
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Summary
Side return extensions are one of the best investments you can make in a London terraced house. For £60,000-£95,000 in 2026, you transform a narrow, dark kitchen into a light-filled family space that typically adds more value than it costs.
While most require planning permission and Party Wall agreements, approval rates are high (85-90%) when properly designed. The process typically takes 6-9 months from initial design to completion.
Start with accurate pricing and check your planning requirements before commissioning detailed designs. Our free tools can help you understand costs and planning constraints in under 2 minutes.