SnoGard™ EF Exposed-Fastened Snow Retention

When snow avalanches off a rooftop, it can damage anything in its path. This sudden release of snow can be dramatic—dumping tons of snow all at once. Falling snow forms a temperature-sensitive bond to the surface of a metal roof. As that roof warms, whether from the sun or from building heat loss, the bond with the snow is broken and a thin film of melt water serves to lubricate the roof. This can have dramatic results as a several-ton blanket of snow suddenly slides off the roof and avalanches down upon anything in its path: gutters, vehicles, landscape, even people. Once piled up below, that same snowbank can cause additional troubles, like direct damage to the building walls or even indirect damage caused by funneling melt water into, rather than away from, the wall. This is what makes snow retention devices desirable: they hold the snow back and allow it to leave the roof slowly, either in small amounts of snow or as meltwater, avoiding the dual calamity of the avalanche.

It is very difficult to predict how snow banks will shear when only a portion of the bank is restrained. It will not, however, shear in a straight line from the end of the snow retention system (also known as a snow guard) up to the ridge. This is a certainty. Rather, it will shear in a diagonal line toward the ridge. The angle of that line becomes more acute as the slope of the metal roof increases, resulting in a large, wedge-shaped bank of snow being supported by the system -- not a small, rectangular shaped bank. This is because the snow bank has cohesive strength within itself. The cohesive strength varies with the density and temperature of the snow bank, which always changes. Hence, the angle of shear is impossible to determine with any certainty.