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Cost Estimator
How Much Does a Home Extension Cost?
Estimate home extension costs based on extension type and size.
📍Your location
⚙️Job details
Factors that affect cost
- Extension type and number of storeys — double-storey adds more value per £ spent
- Specification of finishes, glazing, and structural complexity
- Planning and building regulations fees (typically £500–£2,000)
- Groundworks and foundation type required
💡 Money-saving tips
- 1.Obtain planning permission before getting detailed quotes — saves wasted design costs
- 2.A single-storey rear extension under 4m (detached) or 3m (semi/terrace) often falls under permitted development
- 3.Hire an architect or designer — their fee pays for itself through better design and contractor management
- 4.Build in a 15–20% contingency; extension projects often uncover unexpected issues