The upper story of part of this house (1930s) is tile-hung stud work on top of the old attached garage (which itself has been turned into accommodation). So, plenty of room but that part of the house is always cold in winter. Starting to understand why now.
Floor is up in one of the bedrooms, as plumber is running new pipework. So he's taken up the chipboard floor parallel and near to the north-facing outside wall. The floor joists there run north-south, and stretch out to the OSB sheet that the tiles are hung off. The sole plate for the upper story stud work is on top of the joists. So far so good.
However, although there's a fair bit of insulation (fibreglass under the floor, it doesn't extend out under the sole plate to the OSB. You can reach under the sole plate and feel the OSB sheet - only mm from the hanging tiles. Looks like it's missing a good couple of feet of insulation there, probably all the way along that wall. We can probably fix it in that bedroom, and other rooms as we go.
But what a gash job.