I realise this is a bit of a finger in the wind type question, but here goes. We have had a single storey extension finished recently ~2 to 3 months ago. I notice that it's losing around 5-6 degrees overnight. Is this normal? The heating is a 1kw rad in each room with 1 being 2.5m X 3.5m and the other 2m X 2.5m. the bigger room does have a window in that's about 1.8m wide, and both are essentially 2 outside walls. It's an apex roof rather than a flat roof. There is insulation in there, but not as much as I would have expected, think about 6-10 inches or so (I remember it being the thickness of the joists and they were about that). The loss is from when the heating clicks off at 10pm and it clicks on at 5 am. The drop is from 20ish to 14ish.