When it's cold and frosty in the morning, and I'm out walking the dog contemplating the different methods to assess the impacts of thermal bridging (it's a thing), I often notice how the frost melts at different rates in different areas on different roofs around my neighbourhood.
Some situations:
Vertical striping on the roof is telling me that we've got some thermal bridging going on. Not sure why - could be a cathedral ceiling in there? Maybe the roof has been insulated during recent re-roofing? Not sure exactly why, but it can be dramatic.
Horizontal frost lines on a gable roof suggests we've got a difference in insulation level between the cathedral (sloping) portion of the roof and the area behind the knee-walls. Or maybe some air leakage into the "lower attic" behind the knee-wall?
Way less frost on one roof than it's neighbour is a good indication that the less frosty house:
has a less insulated attic
has air leakage or ventilation issues in the attic (like a bathroom fan that isn't properly vented through a roof vent)
is way warmer inside
Weird patchiness is a head scratcher. My intuition says air leakage but I'm not totally sure.
Lots of melt at the peak of a hip or gable and less lower down (but not as far down as the eaves) suggests some air leakage induced melting, as that warmer air rises within the attic space.