Here is eastern Canada pitched rooves are capable of withstanding about a metre of snow. Wet snow supposedly has a mass of close to a tonne per cubic metre, a c

Here is eastern Canada pitched rooves are capable of withstanding about a metre of snow. Wet snow supposedly has a mass of close to a tonne per cubic metre, a cube of pure water is one tonne at 4C. I can't imagine these devices would weigh more than a tonne (1,000 kg) per square metre.