Snow retention systems...
Snow guards, Avalanche guards, Snow retention systems are protruding metal or plastic devices (or lengths of bars) that are installed in intermittent locations on a roof that is intended to prevent accumulated snow and ice from sliding in great sheets off the roof. They encourage the gradual melt and breakdown of the snow mass into smaller sections. They vary in their method of attachment to the roof, as well as their colour (they usually match the roof or are transparent), and their material (typically, they're made of metal or polycarbonate).
Snow and ice are surprisingly heavy, a single cubic foot of ice weighs more than 52 pounds (24 Kg) and when they avalanche from a roof, they can cause a great deal of property damage and injury. Roof avalanches can injure pedestrians and, bend gutters, and damage vehicles, lower roofs, HVAC equipment, and other property below. This typically happens when warm weather follows a snowstorm, creating meltwater that lubricates the roof.
Snow guard placement should be consistent with the following safety and efficiency standards:
Snow guards should be mounted on the lowest portion of a roofing panel where the snow and ice actually move. Snow guards mounted on a high seam will be ineffective when the snow and ice compact beneath them.
Snow guards should not be mounted beyond the bearing wall on an extended roof section, as this placement can result in ice damming and roof damage.
Snow guards should be installed over sidewalks, doorways, driveways, and anywhere else that people are likely to walk or gather, or where property is stored.
There should not be more snow guards installed than are necessary, as they might allow too much snow to accumulate and damage the roof. Snow guards should be installed in the critical areas listed, but not necessarily in areas where snow and ice can be released safely onto the ground by gravity and natural warming.