Side Return Extension London: Complete Cost Guide 2025
Transform your narrow side passage into valuable living space. Everything you need to know about side return extensions in London, from costs to planning requirements.
Key Takeaways
- Average cost: £55,000-£85,000 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's 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.
Average Costs in London
Side return extensions cost between £55,000 and £85,000 for most London properties. The wide range depends on size, finishes, structural complexity, and your location within London.
| Quality Level | Cost per m² | Total (12m²) |
|---|---|---|
| Budget | £3,500-£4,500 | £42,000-£54,000 |
| Mid-Range | £4,500-£5,500 | £54,000-£66,000 |
| High-End | £5,500-£7,000 | £66,000-£84,000 |
| Premium | £7,000+ | £84,000+ |
Note: These figures assume a typical single-storey side return extension of approximately 12m² (1.2m wide × 4m deep × 3m high). Costs can vary significantly based on access, structural work required, and finishes.
Detailed Cost Breakdown
Typical 12m² Side Return Extension
Typical Size and Dimensions
Most London side return extensions follow these dimensions:
Width
- Typical side passage: 1.0-1.5m
- After extension: Full width to boundary (minus 150mm for gutters)
Depth & Height
- Depth: 3-5m (matching existing rear wall)
- Height: 2.4-3.0m internal ceiling
Result: Typical addition of 10-15m² of floor space, enough to significantly enlarge a kitchen or create an open-plan kitchen-diner.
Planning Permission vs Permitted Development
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)Kitchen Integration Benefits
The primary reason for side return extensions is to create a larger, more functional kitchen. Benefits include:
Island or Dining Table
Extra width allows for a kitchen island or proper dining table
Natural Light
Side-facing glazing brings light into previously dark galley kitchens
Better Circulation
Room for multiple people to work and move around comfortably
Storage Space
Extra width for full-height cabinets and pantry storage
Light and Space Improvements
Beyond the square footage, side returns dramatically improve how the space feels and functions:
Natural Daylight
Most Victorian and Edwardian kitchens are galley-style with windows only at the front and rear. The side return adds a third light source, transforming a dark corridor kitchen into a bright, inviting space.
Glazing Options
- Full-height glazing: Floor-to-ceiling glass on the side wall
- Roof glazing: Skylights or glass roof panels for overhead light
- Clerestory windows: High-level glazing for privacy while maintaining light
- Bi-fold or sliding doors: Connecting to side access or patio areas
Perceived Space
Even a modest 1.2m of additional width makes a dramatic difference. The kitchen shifts from a narrow corridor where two people can't pass to a proper room with breathing space.
Terraced and Semi-Detached Specifics
Terraced Houses
Most common for side return extensions in London:
- Side passage typically 1.0-1.5m wide
- Shared party wall on one side (requires Party Wall Agreement)
- Boundary wall on the other side (may be shared)
- Usually requires planning permission (too narrow for PD)
Semi-Detached Houses
More flexibility but similar considerations:
- One side is detached (may allow PD if wide enough)
- Party wall on attached side requires Party Wall Agreement
- May have driveway access on detached side
- Check if driveway/access must be maintained
Design Considerations
Roof Design
Your roof design significantly impacts both appearance and budget:
- Flat roof with rooflight: Most economical option (£6,000-£10,000)
- Pitched roof: Traditional look, better for matching existing (£8,000-£12,000)
- Full glass roof: Maximum light, contemporary aesthetic (£12,000-£18,000)
- Hybrid (solid + glass): Balance of light and insulation (£10,000-£15,000)
Wall Finishes
External materials should complement your existing house:
- Match existing brick for visual continuity (planners often prefer this)
- Render for a clean, modern look (may need planning justification)
- Consider privacy screening if facing neighbor windows directly
- High-performance glazing (U-value ≤1.4 W/m²K) required by Building Regs
Internal Layout
Plan carefully to maximize the new space:
- Position island or dining table in the widest part
- Consider removing internal walls to create open-plan flow
- Maintain 1.2m circulation space around work zones
- Plan for underfloor heating (works well with large floor areas)
Building Regulations Requirements
All side return extensions require Building Regulations approval for:
Structural Stability (Part A)
Foundation design, wall ties, roof structure, and connection to existing building
Fire Safety (Part B)
Fire-resistant construction, escape routes (if altering access), and compartmentation
Energy Efficiency (Part L)
Insulation standards (U-values), glazing performance, heating system upgrades, and SAP calculations
Ventilation (Part F)
Kitchen extraction, background ventilation, and potential whole-house ventilation requirements
Drainage (Part H)
Rainwater drainage, foul drainage connections if relocating kitchen services
Building Control: You'll need Building Control inspections at key stages (foundations, DPC, drainage, completion). Budget £800-£1,500 for Building Control fees depending on your borough.
Party Wall Requirements
Nearly all side return extensions require Party Wall Agreements under the Party Wall Act 1996.
What Requires Party Wall Agreement
- Building on or up to the boundary line with your neighbor
- Building within 3m of neighbor's structure (with foundations deeper than theirs)
- Inserting a damp-proof course into a shared wall
- Any works to a shared boundary wall
The Process
- 1Appoint a Party Wall Surveyor (or use an Agreed Surveyor with your neighbor)
- 2Serve notice to neighbors at least 2 months before work starts
- 3Surveyor prepares Party Wall Award (legal document)
- 4Schedule of Condition prepared (photographs/description of neighbor's property)
- 5Work proceeds under terms of the Award
Typical Party Wall Costs
Important: Don't start work without completing the Party Wall process. Your neighbor can obtain an injunction to stop construction, and you may have to undo completed work at your own expense.
Get Your Side Return Extension Cost
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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.
Will my neighbor object to the Party Wall works?
Most neighbors consent to Party Wall notices because the process protects both parties. Even if they "object," this simply means they want their own surveyor (at your expense) to review the works. It doesn't stop the project—it just formalizes the process.
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 £80,000-£130,000 for combined side return and rear extension (depending on size and finishes).
What's the best roof type for a side return?
For maximum light: glass roof with structural glazing bars. For best insulation: flat roof with one or two large skylights. For traditional aesthetics: pitched roof matching your existing. Most London planners accept any of these if well-designed and proportionate.
Will a side return add value to my home?
Yes, typically £50,000-£80,000 in added value for London properties, 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'll 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.
What if I don't have side access?
Materials can be carried through your house, though this increases labor time and cost (add 10-15%). Alternatively, if neighbors agree, you can request temporary access through their property (formalized in writing). Some builders use mini-diggers that fit through standard doorways.
Summary
Side return extensions are one of the best investments you can make in a London terraced house. For £55,000-£85,000, 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.