How to prevent ice dams on roofs

Anyone who lives in cold climates should take preventive measures to protect their home from the formation of ice dams.

Ice dams occur when roof gutters become clogged with ice and debris. As rainwater or snowmelt runs off the roof into the gutter, it is trapped between the ice inside the gutter and the roof tiles. With nowhere for runoff to go, the water can back up and pass under the roof tiles. Once the water passes under the shingles, it can remain there for an extended period of time undergoing a long series of freeze / thaw cycles. If water remains under the roof shingles, it won’t be long before the water begins to damage the roof deck and rot the wood.

Repairing water damage as a result of ice dams is expensive.

Avoiding ice dams is easy and inexpensive. Avoid ice dams during new construction or re-roofing by employing the following measures:

1. When installing a new roof, always install a good quality ice and water barrier in the first 3 feet of all roof eaves at a minimum (or 2 feet after the first interior wall). Lower pitched roofs may require 6 feet of ice and water barrier or more. The minimum building code for most Wisconsin municipalities requires that the ice and water barrier extend from the edge of any roof overhang to two (2) feet beyond the interior wall. In most situations, the ceiling panel (cantilever) is 1 foot or less wide. Therefore, the standard ice and water barrier manufactured in three (3) foot wide rolls will meet the minimum building code. This is why most roofers include one row (first three feet) of ice and water barrier in their roofing offerings. If you have a wider soffit, carefully read the minimum building code for roofs in your municipality and be prepared to install more than one row of ice and water barriers. Also note that this is the “minimum” building code. Generally speaking, more is better in this situation, but the ice and water barrier is relatively expensive compared to the traditional tar paper base. One must weigh the costs and benefits of going beyond the minimum building code in this situation.

2. Install gutters and downspouts large enough to handle all the water runoff from your roof. Most contractors will be able to estimate the required gutter capacity based on the size of the roof. Larger roofs will require larger gutters with more water capacity. Custom seamless gutters are a bit more expensive than pre-made gutters, but they pay for themselves once durability and maintenance is considered. Always make sure water has a clear path out of downspouts and away from the foundation of the house.

3. Optimize roof ventilation by balancing intake vents (soffit or gable vents) and exhaust vents (ridge vents or box vents). There should be a 50/50 balance between the cold air inlets and the hot air outlets in the attic space directly under the roof deck. Cold air from outside enters through the intake louvers and pushes warm air out of the attic space through the vents in a properly functioning system. Without proper ventilation, hot air is trapped in the attic space. This hot air will heat the roof and melt accumulated snow. At the same time, cold air outside can freeze melting snow and create ice, and the freeze-thaw cycle continues.

Ice dams on existing roofs can be prevented by following the steps below:

1. Maintain and clean your gutters and downspouts regularly. Make sure the water can flow freely and away from your roof. Once a downspout becomes clogged and the water freezes inside a gutter, it’s too late! Installing gutter guards is a good investment that will save you time and prevent clogs.

2. Install heated roof cables in areas where ice dams frequently occur. Heated roof cables are readily available, low voltage heating elements attached to the eaves and gutters of your roof. These cables can prevent ice from forming in the first place.

3. Install additional insulation in attic spaces to ensure that hot air from the home does not escape into the attic and heat the roof.

4. Calculate the amount of roof ventilation that exists in the attic space. Add intake or exhaust vents if there is less than 1 square foot of ventilation area per 300 square feet of attic floor space. There should be a balance of 50% intake ventilation and 50% exhaust ventilation.

Preventing ice dams and the damage they will cause can be as easy as cleaning your gutters regularly. If you can’t do it on your own or if you have frequent ice-blocking areas, call a reputable local roofing company for help.