Each winter season, ice and snow build-up on surfaces of buildings discharges onto sidewalks and streets below, risking damage and creating potential dangers for passersby. Concerns have become more widespread with the growing popularity of exterior shading devices to limit solar gain and facilitate natural daylighting.
As covered in ASCE/SEI 7 “Minimum Design Loads for Buildings and Other Structures,” ice build-up is possible across almost the entire US. The thickness and weight of ice and snow build-up depends on climate, but every surface - vertical, horizontal or sloped - will inevitably accumulate ice under certain weather conditions. Melting and refreezing of drifted snow create added concerns. For urban sites, ice can also impact nearby buildings and surfaces, within the “footprint” of wind-blown discharge.
It is important to note that falling ice and snow is not a “sunshade problem,” but rather, an inherent characteristic of the built environment. Sun shades are only one source of ice and snow on the exterior of buildings. Aluminum sun shades are not protection from falling ice; instead, they should be considered both sources and targets.
Areas with pedestrian access should be protected from falling ice and dense snow, or such access curtailed, as soon as the potential for discharge exists. Similarly, if there is any indication that falling ice has impacted sun shades or other projections, inspection and remediation should follow as soon as possible.
AAMA 514-16 “Standard Test Method for Static Loading and Impact on Exterior Shading Devices” now provides design teams with a uniform laboratory procedure for project-specific evaluation of downward static ice and snow loads, as well as falling ice impact loads on horizontal exterior shading devices.
