Ice dams are common throughout the Northeast. The necessary ingredients for ice damming to occur are heat, seeping into the attic from the living space below, cold air from outside, and snow.
How do ice dams form?
Warm air from within the living space escapes into the attic through holes, cracks and other penetrations and causes the underside of the roof sheathing to warm up. The only part of the roof sheathing that does not get warm is at the overhang which is not above the living space and therefore remains cold.
The warm sheathing causes the snow above to melt and the resulting water runs down towards the cold overhang where it begins to freeze. As a result, a ridge of ice can form along the entire length of the home at the overhang.
This ridge of ice or ice dam, causes the flowing water to back up along the length of the overhang where it can get under the roof shingles and seep into the home.
Permanent Fixes for Ice Dams
Consider this: Ice dams occur because heat from the living space escapes into the attic causing snow on the roof to melt. So the goal is to keep the entire attic space at the same temperature as the ambient (outside) air.
Measures such as air sealing, adding additional insulation, and increasing ventilation will help tremendously. As a bonus, you will also be increasing the durability and the energy efficiency of your home in the process.
The goal of air sealing is to close off all penetrations leading from the living space into the attic. Here are some things to look for:
- The attic access. Make certain the material blocking this hole whether plywood, sheetrock, or a folding stairway, is tightly weather-stripped and has insulation applied to the top.
- Look for chimneys running from the basement up through the attic. Large gaps, three inches or more in width on all four sides of a chimney are not uncommon. In most cases, these gaps lead all the way down to the basement. Large amounts of warm airflow upwards through these gaping holes by a process called the stack effect. Note, because a chimney is a potential heat source, these areas should be tightly sealed using non-combustible materials such as metal flashing and fireproof caulk.
- Penetrations caused by wires, plumbing, and vent pipes are usually larger than they need to be and the excess gaps should be filled with expanding foam.
- Recessed lights, especially older versions are not air-tight. These older light fixtures require air to circulate around them to help keep them cool. For this reason, it is not a good idea to seal or insulate over them. Instead, consider replacing these outdated fixtures with an IC-rated fixture that come tightly sealed and can be insulated over.
- Interior partitions are full of warm air. They are located within the conditioned space and end at the attic floor. Both sides are covered with sheetrock or plaster, each of which have open seams allowing warm air to flow upward and into the attic. Most homes have many interior partitions so sealing these open seams is important.
- Seams on exterior walls are treated in the same way as interior partitions.
When properly done, air sealing provides a great defense warm air and moisture infiltration and is the first step in the ice damming prevention process.
Bathroom exhaust fans
It is crucial that bathroom fans are vented directly to the outside and not directly into the attic space. These units are designed to move large amounts of warm, moisture-filled air. A cold attic is the last place you want this warm moist air to concentrate.
For best results, bathroom fans should be vented upward through the roof using a bath fan roof cap. The hose connecting the bath fan to the roof cap should be insulated to prevent condensation build-up as the warm air flows through the cold attic.
Ductwork located within the attic space
During the winter your ductwork moves warm air throughout your home. Ductwork running through an attic must be properly sealed and fully insulated to prevent heat loss. Properly sealed and insulated ductwork can also lead to huge energy savings.
Adding additional insulation helps to keep the heat where it belongs, within the living space. The best insulation for this application is either blown cellulose or blown fiberglass. They are relatively easy to install, can be added over existing insulation and once settled form a seamless blanket.
Most attics in older homes contain far less insulation than new homes being built today. Like ductwork, adding insulation not only helps to prevent ice damming, it may also lead to huge energy savings.
For best results, install a continuous ridge vent coupled with a continuous soffit vent. This arrangement creates a natural airflow, bringing cold air in from the soffit and drawing it up and out through the ridge thus keeping the underside of the roof sheathing cool and dry as it circulates.
Wind baffles should be installed between rafters and extend downward into the soffit. When properly installed they form a channel designed to maintain uninhibited airflow.
If properly followed these helpful tips will prevent ice damming in most attics.
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