Wow! What a first snowfall! Some people are still digging themselves out of the mess.
For all of you who might be wondering, "Are we going to see the same issues with Ice Dams that we had during the winter of 2010 / 2011I?" That winter started out the same way with a huge snow storm on or around December 11th. Read on to find out more about how ice dams form and how you can prevent them.
What is an ice dam?
An 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. The water that backs up behind the dam can leak into a home causing damage to walls, ceilings, insulation and other areas.
The picture posted of the cross section of a home shows an ice dam.
How do ice dams form?
This is a complex answer. An interaction between the amount of heat loss from a house, snow cover, and outside temperatures leads to ice dam formation. If higher portions of the roof's outside surface is above 32°F while lower surfaces are below 32°F, and outside temperatures are below 32°F and sustained for a period of time ice dams can form.
The snow on a roof's surface that is above 32°F will melt. As water flows down the roof it reaches the portion of the roof that is below 32°F and freezes. Voila!—an ice dam.
The ice dams grow when the melting snow above them, limited to the portions of the roof that are on the average below 32°F, becomes water and backs up behind the ice dam. This water remains a liquid and finds cracks and openings in the exterior roof, then flows into the attic, into exterior walls, and through the ceiling and insulation.
Why are there different roof surface temperatures?
Most ice dams form at the edge of the roof, which we can conclude does not have a heat source. The heat is coming another source which is usually the inside of the home itself. The heat gets transferred through convection, conduction, & radiation.
In a house, heat moves by conduction through the ceiling and insulation through the ceiling (see diagram). It is important to use insulation with high R-value per inch to reduce this heat loss since in many homes, there is little space in areas like this.
The photograph of the white home shows the points of heat loss that can be clearly seen in the areas with no snow. The ceiling below this area needs to be examined for air leakage, missing or inadequate insulation, leaky or poorly insulated ductwork.
The photograph of the brick home shows high heat loss from the roof. There is very little snow left on the roof and at its edge is both an ice dam and a "beautiful" row of icicles. The unusually high heat loss on this roof has caused both an ice dam and icicles.
So it is primarily heat flowing from the house that is causing the nonuniform temperatures of the roof surface leading to ice dams.
Preventing and dealing with ice dams
Ice dams are prevented by controlling the heat loss from the home.
- Remove snow from the roof. This eliminates one of the ngredients necessary for the formation of an ice dam. A "roof rake" and push broom can be used to remove snow, but may damage the roofing materials.
- In an emergency situation where water is flowing into the house structure, making channels through the ice dam allows the water behind the dam to drain off the roof. Hosing with tap water on a warm day will do this job. Work upward from the lower edge of the dam. The channel will become ineffective within days and is only a temporary solution to ice dam damage.
- First, make the ceiling air tight so no warm, moist air can flow from the house into the attic space.
- After sealing air leakage paths between the house and attic space, consider increasing the ceiling/roof insulation to cut down on heat loss by conduction.
- Natural roof ventilation can help maintain uniform roof temperatures, but if the long-term actions described here are done effectively, then only small amounts of roof ventilation are needed to maintain uniform roof surface temperatures.
If you have an Ice Dam:
Interior damage should not be repaired until ceilings and walls are dry. In addition, interior repair should be done together with correcting the heat loss problem that created the ice dam(s) or the damage will occur again.
Step 1: Call Paul Davis for an assessment of your issues. We can help you work with your insurance company to see if it is worth filing a claim or just restoring on your own.
Step 2: Remove the ice dam. Have a profeesional remove it with a hot steam power washer.
Step 3: Drying what is wet. Have a professional dry the materials properly whenever possible. If materials have been compromised then they need to be removed and replaced.
Step 4: Restoration. Have a professional restoration contractor structurally and aesthetically restore your home.
Step 5: Prevention. During the restoration process fix the ventilation & insulation issues to prevent further damage from happening
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For more resources and information: http://www.extension.umn.edu/distribution/housingandclothing/dk1068.html#new