Side Return Extension Guide: Costs, Planning & Design 2026
A side return extension fills the narrow alley that runs alongside your kitchen — typically found on Victorian and Edwardian terraces. It is one of the most transformative home improvements for terraced properties, turning a narrow galley kitchen into a bright, open-plan kitchen-diner.
What you need to know
What is a side return extension?
The 'side return' is the narrow passage (typically 0.9m–1.5m wide) between your house and the boundary wall that leads to the back garden. A side return extension fills this space and opens it up to the existing kitchen, dramatically increasing width and light. Most side returns are single-storey with a flat or glazed roof.
Why it works so well
A side return adds 30–50% more floor area to your kitchen without reducing garden space. The new width allows a proper kitchen island, a dining table, or both. Large glazed panels in the roof flood the previously dark kitchen with natural light. It transforms the most-used room in the house.
Design considerations
The key decisions are: (1) how far back to extend — flush with the existing rear wall, or continue into the garden; (2) roof type — flat, pitched, or glazed; (3) whether to open the full length of the party wall or leave a structural pier. We design layouts that maximise the gained space without compromising the structure.
How much does it cost?
| Item | Typical Cost Range |
|---|---|
| Side return only (8–12m²) | £25,000–£45,000 |
| Side return + rear extension (18–25m²) | £40,000–£70,000 |
| Glazed roof (per m²) | £400–£800 extra |
| Professional fees | £2,000–£4,500 |
| Kitchen | £8,000–£25,000 |
| Party wall (per neighbour) | £700–£1,500 |
Prices based on Dorset rates, 2026
Planning permission
Most side return extensions fall under Permitted Development as they do not project beyond the existing rear wall. However, if your property is in a conservation area or if the side return extends into the garden beyond the rear wall, you may need planning permission.
A side return that does not project beyond the existing rear wall and stays below the existing eaves height generally qualifies as PD. If combined with a rear extension, the rear element must comply with standard PD depth limits (4m/8m).
Building regulations
Building Regulations apply. Key considerations include: opening up the party wall (structural engineer required), drainage connections (the side return often contains the soil stack), damp-proofing where the new structure meets the existing house, and ventilation requirements.
Typical timeline
| Phase | Duration |
|---|---|
| Design | 2–3 weeks |
| Planning (if required) | 0–8 weeks |
| Structural calcs | 1 week |
| Build | 8–12 weeks |
Frequently asked questions
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