Key Takeaway
Work out an indicative extension budget by size and type, then check the cost and planning context for your address.
How do project costs and planning routes compare?
Extensions add to the building, while loft and garage conversions work with existing space; each has different structural and planning considerations. The route depends on the property, so these comparisons are not an individual planning decision or quotation.
| Project | Typically needs planning? | Main cost factors | Typical design route |
|---|---|---|---|
| Single-storey extension | May qualify for permitted development if all conditions apply | Footprint, foundations and specification | Survey, layout, planning check and technical drawings |
| Two-storey extension | Depends on the design and permitted development limits | Structure, roof design and specification | Survey, planning check and coordinated structural information |
| Loft conversion | Some roof works may qualify, subject to restrictions | Roof type, stairs and structural work | Roof and layout assessment, planning check and Building Regulations |
| Garage conversion | Often possible without a planning application, but exceptions apply | Insulation, structure and services | Survey, planning check and Building Regulations design |
Start with your address and project type
Use our free extension cost calculator and planning check to explore an indicative budget for a single-storey or two-storey extension. The result is not a contractor quotation.
Have a project in mind? Start with a few details about your home.
Build an initial project budgetSingle-storey and two-storey budgets
Choose the proposed extension type and size in the calculator. Measure both floors when budgeting for a two-storey extension. Our two-storey cost guide explains the existing indicative £1,800–£2,600 per m² + VAT range and worked examples.
Allow for the full project scope
Building work, professional and statutory fees, kitchen and bathroom fit-out, unusual groundworks and contingency are separate budget considerations. Compare written contractor scopes and check VAT treatment before comparing quotations.
Ready to apply these ideas to your own home?
Check your project costsDesign and planning checks
Design packages start from £1,950 + VAT. Compare the existing package scope. Structural calculations are prepared by an independent qualified structural engineer. Planning restrictions and permitted development rights must be checked for the property.
A useful next step for your home
Share a few project details to explore an initial budget and planning view.
Get an initial cost and feasibility view