Two things decide what an extension costs in Nuneaton, and neither of them is the size of the room.
The first is what the brick has to match. This is a town built largely out of its own clay, and older Nuneaton brickwork has a colour and texture that no standard modern stock reproduces off the shelf. On an extension that will be seen from the street, and particularly in the Abbey or town centre conservation areas, matching is a sourcing exercise that starts at the quotation rather than an afterthought at first fix. We would rather spend a morning finding the right brick than a decade looking at the wrong one.
The second is the ground, which is covered properly on our groundworks page but belongs in any extension conversation here. Nuneaton has been quarried, mined and dug for clay, and the difference between plots is sharper than in most towns.
The planning position is otherwise ordinary. On the interwar, post-war and modern housing a single storey rear extension of up to four metres on a detached house or three on a semi can fall within permitted development. In the Abbey conservation area an Article 4 direction has removed rights that apply elsewhere, so check before assuming.
There is also the larger home extension route on the unlisted stock: up to eight metres on a detached house or six on any other, by prior approval, with neighbours notified and an answer in about six weeks. Our extensions work is described in more detail there.