Ideally, the roof should have a nice even coating of snow across the entire roof. This indicates that there is a slow even release of heat through the ceiling and thus through the roof. In other words, the airsealing and insulation are working properly and the insulation is even and at a reasonable depth. Remember, the insulation only slows down the heat flow, it does not stop it. In general, more insulation means a slower release of the heat and without airsealing the insulation can not do its job properly.

This older house has some obvious problems in the center of the house. Most likely a combination of air leakage and inadequate insulation. Additionally, the skylight does not look to have been done well from an insulation/airsealing perspective. The garage is on the left where the snow is nice and even.

This newer house is near the ideal image house. The room above the garage most likely has a sloped ceiling(cathedral ceiling) on either side of a center flat (attic ceiling). The insulation in this cathedral section is questionable. Note the roof of the house just beyond this one (far left side of image). It is solid white (i.e. good snow coverage).

This is one of the most interesting houses I found that day. This roof faces North, so sun cannot be blamed. I would guess that the upstairs room was cold , so they added insulation to that section of the ceiling/roof, but did not fully airseal. The rest was not fixed and shows lots of heat loss, probably from a combination of no airsealing and inadequate insulation. Note the garage section of the roof has the least amount of snow (meaning the most heat flowing thru it). This is most likely because the wall insulation and airsealing between the upstair room and garage attic was poorly done.

This newer house shows signs that the vent stack was not airsealed properly, see the dip in the snow to the right of the vent. Additionally, there is something going on in the last bay of the bump out, where there is almost no snow at the peak.

This newer house clearly has a lot of heat leaking into the garage attic from the main house. Yes, it is South facing , but check out the porch roof and the house beyond (no it is not due to the South facing roof)

Notice all the depressions in the snow on either side of the left most vent stack and other places. Most likely an airsealing issue.

This apartment complex was brand new, it had just opened a couple months earlier, but there is clearly a problem in the left side of the three story section. The rest of the roof appeared to be evenly coated with snow

This commercial building has a dropped ceiling and the HVAC system is in the attic. Clearly there is no airsealing and inadequate insulation. By the way the lines are the trusses, if you look closely you will notice that the trusses are actually providing more insulating effect from all the heat leakage into the attic.

This metal roof house is just to show that this type of roof is more difficult to analyze since we can not tell if the snow slid off due to weight or melting. Note: the center section of the roof is slightly shallower than the left or right sides.