How long does an extension take?
Allow around four to nine months from first visit to completion for a typical single-storey extension: roughly 4 to 12 weeks for design and drawings, up to 8 weeks for planning if needed, a few weeks for building regulations and ordering, then 10 to 16 weeks on site. Two-storey extensions take longer on site, and permitted development projects can start sooner.
How long does each stage take?
| Stage | Typical time |
|---|---|
| Survey and design | 4 to 12 weeks |
| Planning application (if needed) | 8 weeks from validation |
| Prior approval for a larger rear extension (England) | 42 days |
| Building regulations approval and structural design | 3 to 6 weeks |
| Party wall process (if needed) | 1 to 3 months |
| Single-storey build | 10 to 16 weeks |
| Two-storey build | 14 to 24 weeks |
| Loft conversion | 6 to 14 weeks |
What causes delays?
Late decisions on doors, glazing and kitchens (which have long lead times), slow party wall responses, unexpected drains or poor ground, and wet weather during groundworks. Ordering long-lead items early is the single most effective way to keep a build on programme.
Related projects
This guide is general information about building work in the UK, not legal or tax advice. Rules change, so check the current position for your property with the council, HMRC or a qualified adviser before relying on it.