ASCE 7-98 Code Snow Loading Analysis - Snow drifts are frequently observed at roof steps, that is, at the common wall between two nominally flat roof surfaces at different elevations. When wind blows from the lower roof towards the upper roof, some of the snow on the lower roof is transported towards and settles at the roof step, resulting in a windward roof step drift on the lower-level roof. When wind blows from the upper roof towards the lower roof, some of the snow on the upper roof settles on the lower roof adjacent to the roof step, resulting in a leeward roof step drift on the lower roof. Current building code provisions relate the size of these drifts to the size of the snow source area (i.e., upper-roof length for leeward drifts).
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