How do I bathroom / kitchen / extension? etc.

No. He had a temporary wooden shed thing, that was almost the size of the house, built right up to the boundary. When I moved in and spoke to him about party wall stuff he said he'd like to have an extension too, so I agreed to build the wall in a way that would let him do that in future. But currently he doesn't live there, the windows are broken, there's no floor and the kitchen extension is separating from the main house enough to fit a fist in, so....