Do I Need Planning Permission for a Two-Storey Rear Extension? (2026)
Usually yes. A two-storey rear extension can sometimes fall under permitted development (PD), but the limits are tight: the extension can extend no more than 3m from the original rear wall, must not come within 7m of the rear boundary, the roof pitch should match the existing house, and upper-floor side windows must be obscure-glazed and non-opening below 1.7m. Miss any one of those and you need a full householder planning application. This guide walks the exact rules, the cost and time to apply, and how to maximise your chance of approval.
When a Two-Storey Rear Extension Is Permitted Development
All of these must be true to avoid a full planning application (England, 2026):
- Depth ≤ 3m from the original rear wall (single-storey rear extensions get more; two-storey is capped at 3m).
- At least 7m between the new rear wall and the rear boundary.
- Roof pitch matches the existing house as far as practicable.
- Eaves and ridge no higher than the existing house; eaves within 2m of a boundary capped at 3m.
- Side-facing upper windows obscure-glazed and non-opening below 1.7m from floor.
- Materials similar in appearance to the existing house.
- Property is not a flat, maisonette, listed building, or in a conservation area / AONB (Article 2(3) land removes most PD rights).
Cost & Timeline of a Householder Application (2026)
A two-storey rear extension also needs a Party Wall Award if it sits on or near a shared boundary, and full Building Regulations approval regardless of the planning route. Before you commission drawings it pays to plan the extension step by step, and when you are ready for prices, use our checklist on how to compare extension builders and check their reviews so you hire on evidence.
Common Questions
Related Guides
More planning and extension guides.
Two-Storey Extension Planning 2026
The full permitted-development rules for double-storey extensions.
Read Guide →