Extension Cost Estimator
Get a rough cost for a single, double, loft or basement extension.
Budget around
Tell us the size and type of extension.
How it works
Per-square-metre rates vary by structure type. Basements need waterproofing and excavation. Lofts are cheaper because much of the shell already exists.
Premium finishes — bespoke joinery, high-end glazing, designer kitchens — typically add 30–40% to the base build.