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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