The Swiss understand the principles of cold country design very well. The old chalets (Figure 7), were divided vertically into three thermal zones with the farm animals on the lowest level, which was often partly dug into the hillside for insulation. Considerable heat was generated by the animals and by the decomposition of their wastes. The heat rose to the next zone and warmed the spaces occupied by the family. Over the family zone was unheated storage for hay and grain that acted as insulation for the living creatures below. This upper space provided summer cooling, as well as a storage area for dry fodder to feed the livestock through the winter when snow was on the ground.

The broad wooden eaves with their stout bracing sheltered the exterior openings in the lower chalet walls, which were sometimes made of square-cut logs and sometimes of thick masonry, decorated with timber balconies. If ice dams did develop, the broad eaves usually kept the dripping water beyond the walls.

The close association between man and beast has its redolent drawbacks. Less rural chalets are heated by beautiful "airtight" stoves, often decorated in ceramic tile, but the attic is usually an unheated storage area. If the average winter temperature in the attic stays below freezing, there will be minimum ice damming at the eaves. Stones hold the snow on the roof, preventing the snow from falling onto people who may be standing below. In addition, the snow provides an insulative cover that retards the heating of the attic by the sun.

In most locations where there is a significant daily temperature swing through the freezing point, the best way to control ice dams is to use a warm roof with additional insulation (R30 or more) so that the building heat melts the snow at a slower rate. In fact, if the snow blanket is thin and the air is cold, there may be no melting from building heat.

Insulation thickness should be reduced at the roof edge, creating a natural temperature gradient so that the water at the eave line is less likely to freeze, and ice dam formation is controlled. A common maintenance mistake when ice damming occurs is to remove the snow a few feet back from the edge of the roof. As the
dam is caused by melted water's contact with cold air, partial snow removal merely changes the point at which the ice dam forms. A sloping roof should either be completely shoveled or not shoveled at all. The building heat should be carried out to the roof edge even in cases where the roof extends out over unheated decks and balconies. A warm roof must never drip onto an unheated roof.

At least the lower 10 feet of all pitched roofs should be underlain with an impermeable membrane, such as Jiffy Seal or Bituthene, to assure water tightness. Sidewalls that abut the eave line of an adjoining roof should be similarly protected. The membrane should be carried up the wall above the top of the largest anticipated ice dam.

Heat tape is often seen laced into roof edges to attempt to control ice dams. It can be effective in piercing the face of the dam and relieving the water pressure that is causing leakage, but sooner or later the snow and ice will slip from the roof, often carrying the heat tape with it. It is not easy to replace the tape under winter conditions. Heat tape cannot be controlled by a thermostat, and manual control requires close attention to snow and temperature conditions.

Vents, chimneys, and other protuberances in the roof plane should be located at the ridge line or in flat portions of the roof. An alternative is to bring them through the sidewalls away from the roof slope. If a chimney or vent must be located at the eave line, it should be heavily reinforced and completely waterproofed, and it should assume a knife-like shape to encourage snow to slip around it.

A rough or ribbed roof will prevent the snow from slipping around a chimney or vent, so such obstructions must be set in a smooth, slippery field that lies well above and to the side of the obstructions.(Figures 8, 9). The tops of vents should be high enough above the roof so the snow will not plug their openings. Plugging can asphyxiate building occupants. Drip lines at roof edges should be beyond balconies and decks, and balconies and entrances below eaves should be protected by roof overhangs. Overhead electrical and telephone lines should never be led into buildings under sloping eaves where sliding snow will break them. Underground utility services are far more practical than overhead ones in the snow country.

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The Neglected Hazards of Snow and Cold
Coping with them demands special design techniques—and stronger codes.
By Ian Mackinlay, FAIA

Article © 1983 Used with permission from the AIA Journal.
Drawings by Jocelyn Bates Helgerson. Photos © 1982 Ian Mackinlay except as noted


Figure 8
Figure 9