The cost of an extension varies hugely, depending on the size and complexity of the project. Traditional brick extensions typically used to cost more than conservatories, but with modern designs, the gap between the styles, and therefore costs, of these is getting smaller.
General builders will tend to quote around £1,500 per metre² for an extension. Average extensions can cost anywhere between £20,000 and £70,000 for the building works, but interior fittings and decorations can cost extra. Flat roofs tend to be cheaper than pitched roofs, but tiled or glass lantern roofs are more stylish. External works like driveways and paths are also not included in the price.