We currently have a flat roofed garage which is at basement level. The side door of our house opens onto the garage roof - the house is set into a slope so at the front (street side) is at ground level with driveway to the side sloping down to the garage, but at the back is at first floor level IYSWIM. There was planning permission (obtained by previous owner) for a two storey extension on top of the garage, but the permission lapsed a couple of years ago.
We are considering a side extension ourselves and believe (although we don't know) that the garage will need demolishing, the foundations strengthening and then building up again. Whether we were to decide on a one or two storey extension can anyone advise on the likely costs of doing this/what percentage extra cost will be incurred in having to strengthen foundations in this way?
A couple of doors down another house of the same design as ours has a one storey side extension over the garage - we don't know the people who live there and they didn't have the extension built so I can't really ask them about it.