Building Costs per Square Metre: How to Compare Your Budget

A price per square metre can help compare early building budgets, but only when you know what the figure includes. A rate from an old article is not a quotation for your property. For a Norfolk extension, conversion or new home, use a current estimate based on your drawings, specification and site conditions.

What does the rate actually measure?

Ask which floor area has been used and whether it is measured internally or externally. Check whether the price covers the whole finished project, the building work only or a shell. Two figures cannot be compared fairly if they use different areas or include different work.

Check the inclusions before comparing prices

• Groundworks, foundations and any known drainage changes.
• Structural work and the connection to the existing house.
• Roofing, glazing, insulation and external finishes.
• Heating, plumbing, electrical work and internal finishes.
• Kitchen, bathroom and other fixtures or allowances.
• Professional fees, surveys, applications and building control fees.
• External works, access arrangements and site clearance.
• VAT: ask how it has been treated in each quotation.

Record exclusions alongside the headline price. Something absent from the builder’s quotation may still need to be included in your overall project budget.

Why similar-sized projects can cost different amounts

Compare the proposed scope rather than assuming an extension is automatically cheaper per square metre than a new build. Access, ground conditions, structural alterations, the condition of existing buildings and your selected finishes can change the work involved. A listed-building repair or barn conversion particularly needs a property-specific assessment.

Separate allowances from confirmed prices

Ask which items are fully specified, which are provisional and how changes will be priced. Keep a separate contingency appropriate to the uncertainties identified by your project team. Confirm how long each quotation remains valid and whether the anticipated start date affects it.

Build a usable project budget

1. Prepare a written brief and the drawings available so far.
2. Use the same scope when requesting comparable quotations.
3. List exclusions, fees, VAT treatment and provisional items alongside each total.
4. Agree a written process for approving changes to price or specification.

Our builder’s quotation guide explains the detail to look for. For an example of the work behind a completed scheme, see our South Walsham extension; its photographs and description are not a price benchmark for another property.

For a project-specific discussion, send us your address, plans and priorities.

Updated September 2026. The previous unsourced price ranges have been removed because they were not a reliable basis for a current quotation.