The top surface of the insulation is warmer than the other surroundings in the attic.In many homes, there is little space in regions like this for insulation, so it is important to use insulation with high R-value per inch to reduce heat loss by conduction. In a house, heat moves through the ceiling and insulation by conduction through the slanted portion of the ceiling. This heat transfers from the sun to you by radiation. Another example of radiation is to stand outside on a bright sunny day and feel the heat from the sun. Heat also transfers from the hot pan to your hand by electromagnetic waves and this is called radiation.The rising air carries heat/energy to your hand. The air right above the frying pan is heated and rises. If you put your hand above the frying pan, heat will reach it by the other two methods.The heat moves from the bottom of the pan to the handle by conduction. A good example of this is the heating of a cast iron frying pan. Conduction is heat energy traveling through a solid.Heat from the house travels to the roof surface in three ways: conduction, convection and radiation. It is primarily heat flowing from the house that causes the nonuniform temperatures of the roof surface leading to ice dams. From the attic it could flow into exterior walls or through the ceiling insulation and stain the ceiling finish. This water finds cracks and openings in the exterior roof covering and flows into the attic space. So the water above backs up behind the ice dam and remains a liquid. The dam grows as it is fed by the melting snow above it, but it will limit itself to the portions of the roof that average below 32F.
As water flows down the roof it reaches the portion of the roof that is below 32F and freezes. The snow on a roof surface that is above freezing will melt. For a portion of the roof to be below freezing, outside temperatures must also be below freezing. These are average temperatures over sustained periods of time. For ice dams to form there must be snow on the roof and, at the same time, higher portions of the roof's outside surface must be above 32 degrees F (freezing) while lower surfaces are below 32F. Heat loss from a house, snow cover and outside temperatures interact to form ice dams. Nonuniform roof surface temperatures lead to ice dams. Take immediate action to get rid of the water source, clean the home environment and maintain its air quality.Prevent the growth of mold and mildew by immediately drying out portions of the house that are wet or damp.Moisture entering the home from ice dams can lead to the growth of mold and mildew. The water that backs up behind the dam can leak into a home and cause damage to walls, ceilings, insulation and other areas. Cross section of house roof with an ice dam What is an ice dam?Īn ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off the roof.
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