The designer of a snow and cold country project must be able to solve problems in a flexible and environmentally sympathetic way: Success requires working with the natural law that governs this domain. Here, nature has a different aspect than in tropic or temperate zones. This is an environment that calls for a great deal of study before design and construction (Figure 1). Each site must be evaluated in terms of its unique microclimate; skipping this essential first step can mean serious consequences for the designer, the builder, and the owner.
Because the impact of snow and cold changes with location, site features, sun angle, temperature, wind direction, snow depth, and other factors, the designer must look beyond the rote application of codes and standards to achieve success (Figure 2). IMA examines the key challenges of this domain—snow loads, ice formation, and water penetration—and how roof form and other design aspects may mitigate or exacerbate these special problems.
Snow loading for all roof types is derived from the site's ground snow load. The basic engineering is explained in "Minimum Design Loads for Buildings and Other Structures," Chapter Seven of ASCE-7 (current edition), published by the American Society of Civil Engineers (ASCE). This document provides ground snow–load reduction factors for flat roofs and sloping roofs (warm and cold, slippery and otherwise) as well as increases for unbalanced loads, drift loads, ice dam loads, and so on. The Commentary section on snow loads cites the methodology, philosophical basis, and references behind the standards set forth in Chapter Seven.
A typical starting point for roof-snow analysis in most codes and standards is uniform loading at some percentage of the ground snow load (defined in ASCE-7). However, such loading does not often occur on most buildings, even those with minimally sloping roofs; snow has a tendency to create eccentric, or unbalanced, loads on roofs due to the vagaries of snow depth, sun angle, wind direction, and other site factors such as hills and trees (Figure 3). Moreover, codes and published design standards, such as ASCE-7, are minimum standards. Snow and cold country design prudence requires thorough analysis of each site and all load aspects.
