FWIW, the hottest side of my house is the West, where it collects the late afternoon sun once it is below the eaves, which have an overhang of 3m and I'd make it 4 or 5 if I were to do it again.
The walls are QCon and there is zero heat transfer there, the problem is the window. During the day there is also significant heat reflected off the concrete driveway, which is west of the house, I hadn't anticipated that.