Side Extension vs Rear Extension: Which Is Better?
A side extension uses the gap between your house and the boundary. A rear extension pushes into the garden. Each has different planning implications, costs, and design outcomes. This guide helps you choose.
The details
Planning differences
Rear extensions have generous PD allowances (4m or 8m depth). Side extensions under PD are limited to: single storey, maximum 4m height, width no more than half the original house width. In conservation areas, side extensions lose PD rights entirely. Two storey side extensions always need planning permission.
Design impact
Side extensions are ideal for: widening a narrow kitchen, adding a utility room, creating a side entrance or boot room. Rear extensions are ideal for: open-plan kitchen-diners, new living rooms, and connections to the garden. The best projects often combine both in a wrap-around extension.
Cost comparison
Side extensions tend to cost more per m² because they typically involve underpinning near the neighbour's foundations and party wall considerations. A 3m × 4m side extension costs £30,000–£45,000. A 4m × 5m rear extension costs £55,000–£80,000. The rear extension gives more space for the money.
| Factor | Side Extension | Rear Extension |
|---|---|---|
| PD depth limit | Half the original width | 4m (8m detached with Prior Approval) |
| Planning needed? | Often (especially 2-storey) | Usually PD (single storey) |
| Typical cost | £30,000–£45,000 (12m²) | £55,000–£80,000 (20m²) |
| Cost per m² | £2,500–£3,750 | £2,750–£4,000 |
| Party wall? | Usually yes | Only if near boundary |
| Garden impact | None | Reduces garden |
| Best for | Utility, side entry, widening | Kitchen-diner, living space |
Our verdict
If you have a side passage and need utility space, a side extension makes sense. If you want a large kitchen-diner or open-plan living, a rear extension gives more usable space. A wrap-around combining both is the premium option.
Common questions
Frequently asked questions
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