We started putting up the joists for the first floor a couple of weeks ago, to provide a platform for building the first floor walls proper. This went really well, with the lounge/study ceiling going up quickly and easily.
However, when we went to start the kitchen ceiling, in the east end of the house, we found someone had beaten us to it.

The location of the nest , in the top corner of the utility window. (back right hand corner of the room pictured above, behind the scaffold tower)
In a corner of what will be the utility window, in a gap between straw and frame, a pair of wrens had quietly built a nest whilst we were occupied at the other end of the house. We found the nest when the chicks (at least three) were about half grown, so we left them to it for a week or so, whilst they fledged and we put up the bathroom floor. I can now report that they fledged successfully around 1 week later, and have been seen fluttering around the garden in an amateurish way since!
Meanwhile, we have finished the joists on the first floor, in preparation for installing the window posts for the bedroom windows, all in advance of our colleagues from StrawWorks coming at the end of July to help us put up the bedroom walls.