Winter is fully upon us and you may have noticed layers of ice and snow building up on your or your roof. You may have also seen this on other buildings, old or new. This type of accumulation, along with a dip in the temperature, is a perfect combination for ice dams to form. In this article, we will address how to prevent ice dams and how to fix an ice dam once one has formed.
What is Ice Damming and how does it Form?
Ice dams are essentially a build-up of ice that is formed on roofs and causes water to back up into a structure. Most ice dams occur when heat escapes from the interior of the structure into the attic and warms the roof; this causes snow that has accumulated on the roof to melt. When the melted snow reaches the cold overhang at the eaves, it freezes again and forms a dam. This process repeats over time, which creates more and more of an ice dam at the eaves of the roof. Keep in mind that if the snow and ice were only melted naturally from the sun, the entire roof would be clear; no white icicles would be hanging from the gutters.
Preventing Ice Dams
The best way to prevent ice dams from forming is to address the factors in your attic that can contribute to ice dams. The most common cause is heat loss. The best way to prevent heat loss is to seal attic bypasses (warm air leaks). Other ways to help prevent ice dams would be having adequate insulation and proper ventilation in the attic. Below, we have carefully outlined the three most common factors that contribute to ice damming.
#1: Heat Loss
Attic bypasses are passageways for warm air to enter into the attic and are the largest contributor to ice dams. In almost every house with ice dams, there will be warm air leaks into the attic space directly below the start of an ice dam. One of the worst bypasses in homes with ice dam conditions is a careless installation of a bath fan. This fan is exhausting warm, moist air directly into the attic at an extremely high rate. Other common places to find bypasses include:
- Furnaces and water heater vents
- Recessed lights
- Plumbing and electrical penetrations that require sealing
- Space around chimneys
If you plan to have additional insulation added to your attic, be sure to first seal the attic bypasses. This is the driving force behind ice dams and even more important than having insulation added. Many people ask the question of, “Can you really ever have enough insulation?” Simply put, if there are voids in the insulation, they need to be fixed. If there isn’t enough insulation, add more.
Proper attic ventilation is also a factor. If cold air is allowed to pass in through a lower soffit vent and up along the entire underside of the roof deck, the outside surface of the roof may maintain a below-freezing temperature, which will help to prevent snow from melting. Ventilation is required for most attics, but it’s the last thing that should be considered when troubleshooting the causes of ice dams.
Possible causes of inadequate ventilation can be that the roof may not have enough ventilation or improperly installed insulation that is covering the eave vents. If the soffit vents are blocked with insulation, you can install air chutes at the eaves to prevent the insulation from blocking the vents.
WIC recommends that these air leaks (attic bypasses) are located and properly sealed by an energy auditor or insulation firm.
Prevention is Key
Remember, ice damming can create large amounts of damage to a home and unnecessary repair costs if the problem is not resolved quickly. Homeowners with ice damming issues will generally experience torn off gutters, loosened shingles and backed up water that will eventually enter the structure through the roof. Once water enters, problems such as peeling paint, stained walls and ceilings, sagging ceilings, and even mold can occur.
Overall, preventing ice dams is simple. Keep the roof surface below 32° F so the snow that accumulates will stay frozen and not melt.