Realistic UK investment ranges for single-storey, wrap-around and double-storey extensions, updated for 2025–2026.
Extension costs vary significantly based on size, structural complexity, specification and access. This guide reflects typical fully managed projects across Milton Keynes, Northampton, Bedford and surrounding areas — including foundations, structure, roof, windows, first and second fix, plastering and decoration. Kitchen fit-out, bi-folds and landscaping are priced separately unless included in your quotation.
£2,200 – £3,200
Per square metre for a fully managed extension shell with standard specification — before kitchen, bi-folds or premium finishes.
£45,000 – £75,000
The most common project — opening the rear of your home to the garden. Typically includes foundations, block and brickwork, flat or pitched roof, windows and doors, insulation, electrics, plumbing first fix, plastering and decoration.
£28,000 – £48,000
Narrow side infill popular on Victorian and Edwardian terraces. Access constraints and party wall considerations often affect cost.
£75,000 – £120,000
Rear and side combined — maximum ground floor space for open-plan kitchen-diners. Higher structural complexity and longer programme.
£85,000 – £150,000+
Ground and first floor space in one project — bedrooms, bathrooms and living areas. Usually requires full planning permission.
Clay soil, trees, drains and poor access increase foundation costs. A site survey reveals the true picture before you commit.
Steel beams, chimney breasts, load-bearing walls and tie-ins to existing roofs all affect engineering and labour.
Standard mid-range finishes vs premium tiles, bi-folds, underfloor heating and integrated kitchens can significantly change the investment.
Full planning applications, Prior Approval and Party Wall notices add time and professional fees — we advise early.
Terraced properties, narrow drives and limited storage increase programme length and labour costs.
Compare like for like: Compare quotations on scope, not headline price. A lower figure that excludes steelwork, Building Control, insulation standards or decoration will cost more once extras are added.
Size, structural work, roof type, specification and access all vary dramatically between properties. Our guide ranges reflect real projects — your free survey produces a fixed quotation for your specific property.
Base build costs typically cover the structural shell, windows, doors, electrics, plumbing first fix, plastering and standard decoration. Kitchen fit-out is quoted separately unless specified in your scope of works.
The planner uses the same rate structure as our surveys — it gives a realistic guide range. Your fixed quotation follows a free property survey where we assess ground conditions, structure and access.
Our quotations are inclusive of VAT where applicable. Planning application fees, structural engineer fees and Party Wall surveyor costs are advised separately where required.
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