Just guessing, but this looks like an uninsulated attic and what you are seeing is the thermal mass of the rafters keeping the roof from dropping below freezing, while the sheathing was able to cool through the night. It's probable that the region had a cold snap and the house was above freezing before this cold night.
No, it was probably insulated just fine, and even with really thick insulation you will still loose heat, just more slowly. The problem is that the insulation typically goes between the studs in a wall and between the rafters in the roof. Both the studs/rafters and the insulation are against the sheathing. Since wood has an insulation value of about R-1 per inch of thickness and insulation has a value of around R-3.5 to R-6 per inch of thickness, more heat transfers through the studs/rafters and can cause the frost to melt. This is what thermal bridging is, and the only way to prevent it is to put continuous exterior insulation between the studs/rafters and the exterior cladding and roofing materials. That is why code in (USA) climate zones 4 and up now requires some amount of continuous exterior insulation. Where I live in climate zone 6 now requires wall assemblies to have 2x6 R-20 walls with R-5 continuous exterior insulation, 2x4 R-13 walls with R-10 continuous exterior insulation, or R-20 continuous exterior insulation with no cavity insulation required.
So in that photo it's not properly insulated?
Just guessing, but this looks like an uninsulated attic and what you are seeing is the thermal mass of the rafters keeping the roof from dropping below freezing, while the sheathing was able to cool through the night. It's probable that the region had a cold snap and the house was above freezing before this cold night.
No, it was probably insulated just fine, and even with really thick insulation you will still loose heat, just more slowly. The problem is that the insulation typically goes between the studs in a wall and between the rafters in the roof. Both the studs/rafters and the insulation are against the sheathing. Since wood has an insulation value of about R-1 per inch of thickness and insulation has a value of around R-3.5 to R-6 per inch of thickness, more heat transfers through the studs/rafters and can cause the frost to melt. This is what thermal bridging is, and the only way to prevent it is to put continuous exterior insulation between the studs/rafters and the exterior cladding and roofing materials. That is why code in (USA) climate zones 4 and up now requires some amount of continuous exterior insulation. Where I live in climate zone 6 now requires wall assemblies to have 2x6 R-20 walls with R-5 continuous exterior insulation, 2x4 R-13 walls with R-10 continuous exterior insulation, or R-20 continuous exterior insulation with no cavity insulation required.