The principle is pretty simple: the less insulation in a house attic or at the rafters, the more heat escapes through the roof. That escaping heat melts the snow. As I'm driving into town, if I see that most of the nearly two feet of snow we received is still sitting there and the depth even, I can be pretty sure I'm looking at a well-insulated and tight house.
I was reminded of this because of an article in the Independent, where they write that Melting snow being used by police to find cannabis farms in the Netherlands; Police are encouraging residents to look for roofs without snow and rat out their neighbors.
“No snow on the neighbours’ roof? You can report suspected cannabis farms anonymously,” police in the city of Haarlem tweeted, urging people to be watchful. The technique appears to be working, with arrests of illegal cannabis growers being recorded across the country since the wintry weather started.
The lack of snow on the roof appears to be a really good indicator; in another bust in Amersfoort, police found 500 plants worth €50,000. ( US $56,492)
“Officers were investigating because the house was completely obscured and the roof was remarkably dry compared to other roofs in the street,” a police spokesperson said.
I would have thought that by now the grow-ops would have learned about the benefits of cool and efficient LED bulbs, but evidently they still prefer fluorescent grow-lux lamps.
There are other, possibly more useful things to be learned from a drive-by energy audit. As Canadian construction know-it-all Mike Holmes writes in the National Post:
After a snowfall, every homeowner should take a look at their roof and check for hot spots — areas on the roof where the snow has melted. It’s normal for some melting around venting and fireplace exhausts, but you shouldn’t see any bare patches on your roof. A snow-covered roof means your attic is doing its job.
Another problem that comes from having either not enough insulation or a grow-op in your house is the possibility of an ice dam. This occurs when the snow on the roof overhang does not melt but the snow over the attic does, thanks to heat loss and insufficient attic ventilation. The unmelted snow acts as a dam, letting water build up behind it until it gets high enough to get under the shingles and into your house. While this might be useful in a grow-op as a sprinkler system, it is not something you want otherwise.
There are many good reasons for having a properly insulated roof; you save money on heating, reduce the risk of expensive roof leaks, and have less danger of killer icicles crashing down on you. And now, you can add to the list that there is less chance that the police might be knocking down your door looking for your indoor marijuana plantation.