GuideUpdated 25/10/2026
How long does an extension take to build?
Short answer
Allow 4 to 6 months from first visit to completion for a typical single-storey extension: around 6 to 12 weeks for design and approvals and 10 to 14 weeks on site. Double-storey extensions take longer on site, and planning applications add time.
Design and approvals
- Survey and design: 2 to 6 weeks.
- Planning application: about 8 weeks for a decision, or a lawful development certificate if it is permitted development.
- Building regulations drawings and calculations: 2 to 4 weeks.
- Party wall notices: 1 to 2 months’ notice in England and Wales.
On site
| Project | Typical time on site |
|---|---|
| Single-storey extension | 10 to 14 weeks |
| Double-storey extension | 14 to 20 weeks |
| Rear dormer loft conversion | 6 to 9 weeks |
| Garage conversion | 3 to 6 weeks |
| Orangery | 8 to 12 weeks |
What causes delays?
Long lead times on glazing and kitchens, bad weather during groundworks, unexpected drains or poor ground, and design changes after work starts. We order long-lead items early and agree changes in writing.
Sources and further reading
This guide is general information, not legal or tax advice. Rules change and depend on your property; we confirm what applies to your project at the survey.
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