Extension Planning Guide
Plan your home extension with confidence. Estimate build costs, project timelines, and check permitted development eligibility instantly.
Estimate Your Extension Project
Enter your extension details below to instantly estimate build costs, expected timelines, and planning permission requirements based on current UK averages.
Project Details
Enter your planned extension specifications
Project Evaluation
Estimated budget, timeline, and planning status
Typical Costs & Planning Rules
General guidelines for extension costs per square metre and Permitted Development (PD) limits in England.
| Extension Type | Avg. Cost per sqm | Permitted Development? |
|---|---|---|
| Single-Storey Rear | £1,500 – £2,000 | Yes (up to 4m detached, 3m attached) |
| Double-Storey Rear | £1,800 – £2,500 | No (Full Planning usually required) |
| Loft Conversion | £1,200 – £1,800 | Yes (up to 40cu.m terraced, 50cu.m detached) |
| Wrap-Around | £1,700 – £2,400 | Subject to combined PD limits |
Extension Planning FAQ
Everything you need to know about navigating the UK home extension process.
Many single-storey rear extensions and loft conversions fall under ‘Permitted Development’ (PD) rights, meaning you do not need full planning permission, provided they meet specific size and height limits. However, double-storey extensions, front extensions, or properties in conservation areas typically require a full planning application.
As of 2024, a standard single-storey extension typically costs between £1,500 and £2,000 per square metre. Double-storey extensions range from £1,800 to £2,500 per sqm, while high-end finishes or London locations can push costs to £3,000+ per sqm.
Under the Party Wall etc. Act 1996, if your extension involves building on or near the boundary with a neighbour, excavating near their foundation, or altering a shared wall, you must serve them a formal Party Wall Notice. If they dissent, a Party Wall Award must be drawn up by surveyors.
A typical single-storey extension takes 3 to 4 months to build after planning and design are complete. Double-storey extensions or wrap-around projects usually take 4 to 6 months, while loft conversions can be completed in 2 to 3 months.