An extension in Coventry starts with two checks that are not needed in most of the towns around the city: whether you are in one of the eighteen conservation areas, and whether one of the fourteen Article 4 directions covers your street. Both change what is permitted, and in a city with that many designations the odds are not negligible.
Where neither applies, and on the interwar and post-war housing out through Coundon, Cheylesmore and Wyken that is usually the case, a single storey rear extension of up to four metres on a detached house or three on a semi can fall within permitted development. Inside a conservation area those figures reduce and a side extension loses its permitted development rights altogether.
The other Coventry specific check is what the house is actually built of. The city has a substantial amount of post-war non-traditional construction, and a house that looks like brick from the pavement is not always brick behind the render. That matters enormously when you want to form an opening in a rear wall, because the structural approach is different and so is the price. We establish the construction type before we design anything into it rather than finding out when the wall is opened.
On the Victorian terraces in Chapelfields and Stoke the constraint is different again: solid walls, shallower foundations than a modern build, and access through the house. All workable, none of it a reason to avoid extending, but all of it a reason to get a price from somebody who has stood in the garden.
Our extensions work is set out in more detail there, including the stages of a build and how the inspections fit around them.