Generally speaking, every part (or room) of a property will need to be classified as domestic or non-domestic. As such, any area that has business (or non-domestic) use is liable for business rates, and any area that has domestic use is liable for council tax. That can mean a single building overall can be liable for both, known as a 'composite' property. If, however, there are areas no longer in use, then these will have to be classified at their last usage.