Side-return extension cost UK 2026
A side-return extension fills the unused side passage of a Victorian or Edwardian terrace, typically adding 8–12m² to the kitchen and creating an L-shaped or open-plan ground floor. Costs land £45,000–£90,000 in 2026 prices, with London projects at the upper end.
Cost guide ranges
| Project type | Standard | Premium | Luxury |
|---|---|---|---|
| Side-return only (8m²) | £35,000–£50,000 | £48,000–£65,000 | £62,000–£85,000 |
| Side-return + rear (12m²) | £45,000–£65,000 | £60,000–£85,000 | £80,000–£110,000 |
| Wrap-around L-shape (15m²) | £55,000–£80,000 | £75,000–£105,000 | £100,000–£140,000 |
| Full open-plan (20m²) | £70,000–£100,000 | £95,000–£135,000 | £130,000–£180,000 |
| London premium | +25–40% on above |
What's typically included
- Removing existing side wall + structural lintel
- Foundations and underpinning if needed (common in older Victorian)
- New cavity wall on side and rear
- Flat or low-pitch roof with skylights / lantern
- Standard glazing (rear bi-fold optional but priced separately)
- Building regs application + structural calcs
- First fix electrics + plumbing for kitchen extension
- Plaster, decoration, basic flooring
What's typically NOT included
- Kitchen units and worktops (£8,000–£25,000+)
- Bi-fold or sliding rear doors (£3,000–£10,000+)
- Roof lantern (£1,500–£3,500)
- Underfloor heating (£60–£100/m²)
- Engineered wood / large-format tile flooring (£60–£150/m²)
- Party wall agreement with neighbour (£700–£1,500)
- Architect drawings + planning application (£2,000–£5,000)
- Structural engineer fees (£800–£2,000)
What drives the price
Side-return projects in London Victorian terraces are some of the most expensive per-m² extensions in the UK. The drivers:
- Underpinning — older Victorian foundations are often shallow. Underpinning the existing party wall before extending typically adds £8,000–£20,000.
- Party wall agreement — both neighbours have to consent. Surveyor fees + complications add £1,000–£3,500.
- Access — terrace access for materials and skips is often through the house. Adds time and cost.
- Open-plan reconfiguration — most side-returns also remove the kitchen-dining wall. RSJ + structural cost £2,500–£6,000.
- Glazing percentage — most go for floor-to-ceiling rear glazing. Bi-folds, sliding doors, roof lanterns add up.
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How we estimated these ranges
This is a guide only. The ranges below are intended for early budgeting and trade benchmarking. They are not a substitute for a site visit or an itemised quote from a qualified tradesperson. Always get a site-specific quote before agreeing work.
What's included in these ranges: typical labour costs, common materials at standard specification, and routine preparation or installation work for a standard project of this type.
What's excluded: unusual access (multi-storey, restricted parking), unforeseen structural issues, specialist design or architect fees, planning and building control application fees, premium or high-end finishes, emergency or out-of-hours work, and regional extremes.
Regional note: London, the South East and remote rural areas can vary significantly from the UK averages shown. London labour rates in particular can run 30–50% higher than national averages on the same scope.
Sources and checks used: publicly available UK trade supplier pricing (2025–2026), common day-rate and labour-duration assumptions used in trade quoting, internal example quote structures from TailoredQuote platform data, and where relevant cross-referenced regional contractor surveys and BCIS-style construction cost data.
Last reviewed: May 2026 by TailoredQuote. Prices in this guide will be reviewed and updated periodically.
Frequently asked questions
£45,000–£90,000 typically, with London projects at the upper end. A wrap-around (side + rear) on a London Victorian terrace commonly hits £100,000+ once kitchen and bi-folds are factored in.
Underpinning (older shallow foundations), party wall agreements with both neighbours, restricted access through the house for materials, and the structural complexity of opening up the existing rear wall all add cost compared to a clean rear extension on a detached property.
Often yes. Side extensions are more constrained under permitted development than rear extensions. Most side-return projects in conservation areas require full planning. Allow 8–12 weeks for the decision.
Almost always — it converts the unused 1–1.5m side passage into usable kitchen/dining space, increasing both the floor area and the property value. Typical ROI in London is 80–120% of build cost on resale.
Related cost guides
Last reviewed: May 2026
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