A single-storey rear extension in Cornwall typically costs between £1,500 and £2,200 per square metre for a standard build. A 20m² extension would therefore cost between £30,000 and £44,000 including labour and materials. Costs vary depending on specification, location and site conditions.
Two-storey extensions offer better value per square metre than single-storey, typically costing between £1,200 and £1,800 per square metre. A two-storey extension adding 40m² of floor space would cost between £48,000 and £72,000. The additional cost of the upper floor is relatively modest compared to the extra space gained.
Key factors affecting extension costs in Cornwall include: size and complexity of the design, specification of materials and finishes, site access and ground conditions, proximity to the coast (which may require additional weatherproofing), planning requirements, and the time of year. We always provide detailed, itemised quotes.
Planning permission applications in Cornwall cost £206 for householder applications (2025 fees). Building regulations approval costs between £500 and £1,500 depending on the size of the extension. Structural engineer fees typically add £500 to £1,500. We can advise on all statutory costs as part of our free consultation.
Timber frame extensions are broadly similar in cost to masonry in Cornwall, though timber frame can save money through faster build times and reduced labour costs. The choice between methods should be based on design requirements, planning constraints and personal preference rather than cost alone.
Kitchen and bathroom extensions involve additional costs for plumbing, electrical work and specialist fittings. A kitchen extension with a new fitted kitchen typically costs between £40,000 and £80,000 depending on kitchen specification. A bathroom extension adds £5,000 to £15,000 for the bathroom fit-out on top of the structural costs.
The most reliable way to get an accurate cost for your extension is to have a detailed design drawn up and obtain quotes from at least three reputable local builders. A.V.A Building & Construction Ltd provide free, no-obligation quotes for all extension projects across Cornwall. Contact us to arrange a site visit.
Watch out for costs that are sometimes omitted from initial quotes: VAT (20% on most building work), skip hire and waste disposal, temporary accommodation if required, landscaping and reinstatement of garden, and snagging and defects rectification. A.V.A always provide fully inclusive, transparent quotes with no hidden extras.
A.V.A Building & Construction Ltd provide free, detailed quotes for all extension projects across Truro, Falmouth and surrounding villages in Cornwall. As members of the Guild of Master Craftsmen, all our work is fully insured and guaranteed.
Contact us today on 01872 719546 or email avabuildingltd@outlook.com to arrange a free site visit and quote.
