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Where Do Ice Dams Form?

Updated: Jun 15, 2023

The five most common areas on your roof for ice dams to occur.

While giant icicles hanging from a roof may look like a thing of beauty, they could be pointing to a severe problem—ice dams. An ice dam is a thick ridge of ice that forms on your roof and prevents the proper drainage of melting snow. Without the proper drainage, the water finds somewhere else to go—usually inside your home. Education is often the key to prevention. This pertains to ice dams, too. To prevent ice dams, you need to understand how and where they form. Armed with this knowledge, you’ll know how to keep them off of your roof and keep their damaging effects out of your home. Although ice dams usually form on the edge of your roof, they can develop on other areas of your roof as well. In this article, we will highlight the five main areas that are most prone to ice dam formation.

1. Eaves

The eaves are the parts of the roof that hang over the edges of a building. They mark the junction of the outside wall of the building and the roof. Eaves not only provide a nice look to a home, but they also have practical purposes. Eaves can help maintain comfortable temperatures in the building. They prevent direct sunlight into windows from the high-level, more-intense summer sun. On the other hand, they allow the low-level winter sun rays to warm a building. One of the other, more practical, purposes of eaves include directing rain and snow off the roof and away from the building. Unfortunately, because of this, and because of the fact that eaves are the coldest part of the roof, they are the most common places for ice dams to form. At least 80% of ice dams are found on the eaves of roofs. These ice dams make those big, sparkly icicles possible, but they are also at the root of a lot of property damage.

2. Valleys

Valleys mark the part of the roof where two roof slopes come together, forming a V shape. This V is the most frequent place for water to run from the top of the roof to the eaves and gutters. This makes valleys an important area of a roof. Valleys are also one of the roof areas most prone to problems. A poorly constructed roof valley can be the cause of water leaks in the home and even roof collapse. Valleys may not have adequate ventilation and may lose heat faster than other roof areas. Because they are the channels for the majority of water runoff and they are a colder area of a roof, they are a place where ice dams commonly form.

3. Roof Openings

Openings on roofs include things like pipes and vents. We're going to also include chimneys and flues in this section. The pipes on a roof are actually part of the plumbing system in the house. They may be referred to as plumbing vent pipes. These vent pipes allow air into the plumbing system. This helps prevent a vacuum-like situation that could slow or stop waste and water drainage. The plumbing vents also prevent dangerous and smelly sewer gasses from remaining in the home. Chimneys and flues are a vital part of a fireplace in your home. They guide the smoke, gasses, and other contaminants up and out of your home. Any opening or area on the roof where heat can escape from below is a possible spot for an ice dam. The ice dams that form around these openings are usually quite small but can still cause water leaks and damage to your home.

4. Skylights and Recessed Lighting

A skylight is a window installed on a roof, allowing natural light into a home. While a skylight may have some venting options, this type of window is fixed and does not open. Skylights may allow unwanted heat to enter the home in the summer. They can hemorrhage precious heat in the winter. This heat loss can contribute to an ice dam on your roof. Ice dams can form both above and below skylights. A skylight-related ice dam is often the sneakiest because it is hard to see from the ground. Recessed lights are installed directly into the ceiling. An interior room with a vaulted ceiling combined with recessed lighting can allow heat to settle near the ceiling. This can lead to some large ice dams.

5. Low Pitch

The pitch of a roof is more commonly known as the roof's slope. This refers to how steep your roof is. A low-pitched roof, or even low-pitched areas on a roof, can sometimes cause water to collect and pool rather than completing its draining journey to the gutter system. Roofs with a low pitch are at risk for ice dams and can have significant damage from even a 1 to 2-inch ice dam. Noone wants to find themselves dealing with an ice dam and the ensuing home damage. The cost and headaches of orchestrating repairs can feel overwhelming. If you live in a climate where snowfall is likely, make sure you are aware of the areas of your roof that are most susceptible to ice dam formation. Once you know the areas of concern, you can look into ice dam prevention products, such as heat trace cable.

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