In contrast to Zermatt, modern towns in mountain settings can be insensitive to environmental factors. Tall buildings can create their own negative microclimates. They can block solar access and shadow streets and parks, making them cold and uninviting. At Snowmass, Colo., the main shopping mall rises three stories high along the south side of a central plaza. Shops with entrances in the shade are not as prosperous as those with entrances in the sun.

Modern cities in the cold country have a problem from the phenomenon known as "aerodynamic shade," created when tall buildings alter wind patterns, sheltering lower roofs from prevailing winds. Unanticipated snow loads can build up on the lower, shadowed structures. Until building codes deal with this special problem, the only solution is to design all buildings for higher snow loads.

Avalanches are a hazard not adequately considered by cities in North America. The typical avalanche slope is a barren, north-facing slope with an angle of 30 to 40 degrees, although avalanches have occurred on hills with all exposures and with slopes from 10 to 60 degrees. Steeper slopes seldom avalanche because the snow slips off before dangerous depths accumulate (Figure 15).

Juneau, Alaska's capital, faces the most severe avalanche danger of any sizable city in the U.S. Major avalanches have swept the west-facing Behrends Chute on Mt. Juneau six times in the past century.
Before 1946, there was only one building in the slide path; today there are 30 houses, a 500-boat marina, part of a high school, and a motel (Figure 16).

In 1972, the Borough of Juneau made an extensive study to define the potential avalanche hazard. One expert predicted that a Juneau house under the Behrends Chute has a 96 percent probability of being hit by an avalanche if it stands for 40 years. The study suggested such precautions as monitoring snowfall, developing warning and evacuation systems, controlling the removal of vegetation and reforesting certain areas. The most practical solution is to construct snow support structures high up on Mt. Juneau and on the other high hills above the city. So far, little has been done, and the people of Juneau seem nonchalant about the danger.

The majority of people in Juneau, together with many others who live on avalanche prone sites, appear to feel that the danger is overstated. This is a curious attitude in a nation that has building codes and zoning laws to protect people from their own folly in choosing to live in the paths of floods, over earthquake faults, or in buildings that are firetraps. Unfortunately, the codes probably will not be changed until possibly hundreds are killed by a great avalanche.

The American Planning Association has no reference manual on avalanche ordinances. A survey of 20 states, 165 counties, and 14 municipalities found that only four states, 15 counties, and six municipalities
had any sort of avalanche zoning regulations. The models for the avalanche zoning ordinances in Vail, Colo., and in Ketchum, Sun Valley, and Blaine County, Idaho, came from Switzerland, where the national government even provides funds to help communities build snow support structures and diverters to keep avalanches from populated areas.

All of the major building codes in the United States have shortcomings in their treatment of snow loads and the special problems of cold country design. Building Officials and Code Administrators (BOCA) and Southern Building Code Congress (SBCC) have almost identical methods for calculating nonuniform accumulations of snow on pitched, curved, or multispan roofs and increased loads caused by snow sliding off sloping roofs onto adjacent roofs, or by projections such as penthouses, cooling towers, and parapet walls'. The codes reflect many of the provisions of the 1972ANSI standards. At a minimum, these codes should be upgraded to completely comply with 1982 ANSI standards.

1

2

3

4

5

6

7

8