How Are Spokane Warehouses Designed for Heavy Snow?

The engineer maps every snow concentration the roof geometry creates. Windward and leeward drifts form against each parapet, with the leeward wedge typically the deeper; the engineer calculates the drift height from the upwind fetch distance — on a big warehouse roof, the fetch is long and the drifts are correspondingly large. Rooftop units interrupt the wind flow and collect drifts on both faces, so the engineer checks the joists beneath each unit for the surcharge. Where the office or entry section rises above the warehouse roof, sliding snow from the upper roof adds to the drift below, and the engineer designs the lower roof framing for the combined load. Unbalanced loading matters on any sloped or gabled portion: wind scours one side and deposits on the other, and the engineer checks the structure for the full unbalanced case even when the uniform case looks comfortable. For the common gable-roofed warehouse, this means one slope carrying a deep drift while the other is nearly bare — a condition that stresses the ridge framing and the columns differentially. The engineer documents each load case on the structural drawings so the reviewer can trace every drift wedge to its supporting member.

Ponding analysis starts with the roof's flexibility. The engineer computes the deflection of the joist-and-deck system under the rain-on-snow load and checks that the stiffness is sufficient for the deflection to stabilize rather than run away — the code's ponding provisions give the acceptance criteria, and long-span warehouse roofs are exactly the structures they were written for. Where the analysis shows marginal stability, the engineer stiffens the framing or adds camber rather than hoping the drains never clog, because drains do clog — with ice, with snow, with debris — and the roof must survive the clogged condition up to the overflow elevation. Drainage is designed in two layers. Primary interior drains or exterior scuppers handle the design storm; overflow scuppers through the parapet, set slightly above the primary inlet elevation, provide the redundant path that engages when primaries block. The engineer sizes overflows for the full rain-on-snow flow, spaces them so no bay ponds excessively, and details the parapet penetrations with proper flashing so the emergency path does not become a leak path. Roof maintenance access is part of the design: drains that cannot be reached and cleared in winter are drains that will fail in winter.