Ice Dams and Roof Durability

Every winter, building owners in McCall and Valley County file millions of dollars in insurance claims for roof leaks, property damage, and mold problems caused by ice damming. On average McCall receives 130" of snowfall annually and the surrounding mountains are blanketed with over 300". It is not uncommon for snow to accumulate on rooftops at depths of over 4 feet for months on end. When this rooftop snow is able to melt and refreeze to form ice dams the effects are often severe and costly for residential and commercial buildings. Over time Ice dams create roof leaks and sliding snow and ice can cause severe structural damage and threaten pedestrian safety. Building owners concerned with the effects of ice buildup spend time and money to chip away ice and snow from roofs creating dangers and liability for those removing the ice and pedestrians below. This annual snow and ice removal is not only dangerous and costly, but also drastically shortens the life of a roof system. Most property damage and insurance claims that are caused by ice damming could have been avoided with proper insulation and roof system design and installation. Despite the common occurrences of ice damming there is a great deal of misunderstanding with regard to the causes of ice damming and its potential for personal injury and building damage.

Roofs should be maintenance free, time and money should not be spent worrying about and snow and ice removal. EnergySeal's stringent installation techniques, high performance products, and systems approach helps create roofs systems that are durable, efficient, and nearly maintenance free.

How are Ice Dams Formed
Poor Insulation
Inadequate Ventilation
Ductwork in Unconditioned Space
Structural Conduction
Solar Radiation

When a leak caused by ice damming is discovered it is typically a homeowners first reaction to blame the leak on a faulty roofing or gutter system, but contrary to what many people believe, ice dams are not caused by a roofing problem, it is actually the ice dam that creates the roofing and gutter problems.

The primary cause of ice damming is excessive heat loss from building interiors through inadequate insulation, but other factors such as flaws in the ventilation system, structural conduction, air vapor transmission, solar radiation, outside temperatures, and snow depth also play a role in accelerating the formation of ice dams.

Ice Damming typically occurs in roof valleys, crickets, and eave edges. Warm air leaking from a building heats the roof system causing the snow to melt. When the melted water hits areas of the roof that are 32°F and below (Typically eave or soffit edges that are not above heated living space), ice will build up and form a ridge or "dam". This ridge of ice prevents melted snow from draining off the roof and causes a pool of water to build up above it, as long as the snow continues to melt the ice dam will grow. The water above the ice dams remains a liquid on the areas of the roof system that are above freezing. The expansion and contraction caused by freeze and thaw cycles of the ice dam can cause damage to the roofing systems. The water built up behind the ice dams finds cracks and openings in roofing materials and flows into the attic space or roof system. From here it can flow into exterior walls or through the ceiling insulation causing substantial damage to the interior of the home in the form of water damage, rotting, leaking, and mold. In addition, the performance of wet insulation is drastically degraded accelerating ice damming even more.

Problems With Ice Dams
Moisture Damage
Structural Damage
Pedestrian Safety
Expensive Ice Removal

High Utility Bills Due to Heat loss

How to Prevent Ice Dams
Building As a System
Attic/Rake Walls
Interior Walls
Crawlspace and Basements

In order to prevent ice damming a total systems approach must be taken. Roof coverings, waterproof membranes, ventilation, and building insulation systems must use the highest performing products. It is important that all building systems work together to prevent the conditions that cause an ice dam, individual elements of the system can limit how the entire system performs as a whole; a roof system is only as good as its weakest link.

It is typical practice for architects and contractors not familiar with building in extreme climates to design inadequate roof ventilation, allow poorly installed and low performance fiberglass insulation throughout the roof system and house, and then try to prevent roof leaks by applying a waterproof membrane under the roof covering. No waterproof membrane is capable of standing up to the weight and force of severe ice damming and without properly installed insulation and ventilation, roofleaks are inevitable.

The first step to eliminating ice dams is to address their main cause, excessive heat loss from heated living spaces. No matter how high the performance of an insulation product is, when improperly installed by inexperience or poorly trained insulation contractors it will be unable to perform under extreme winter conditions when performance is needed most. Fiberglass insulation is the predominant type of insulation in utilized homes, however, even when perfectly installed it is unable to stop air leakage and heat loss. Air freely flows through fiberglass, no matter how high the R-value, and the colder it gets the easier it is for air to flow through it. For more info on R-value Click here.


Another common building practice is to run ductwork and fire place flues through non-conditioned attic space. Ducts and flues radiate and leak warm air into the attic, causing attic and roof temperatures to rise. In order to address the excess heat that is being release by ductwork and heat loss though insulation, contractors will often install more ventilation to fix the problem. The idea is that if more cold air is sucked into the attic it will be able to cool the heated air before it reaches the roof surface, unfortunately this practice is misguided and often makes the problem worse. Adding more ventilation lowers the air pressure in the attic system, the hot air from inside of a house will rise more rapidly and infiltrate through the porous fiberglass insulation at an accelerated rate, causing even more heat loss. The only way for ventilation to work properly is to use an insulation system that stops air infiltration and completely and effectively seals the heated living space from the attic and roof system.

Installing an insulation system that completely seals the roof system from heat loss is no easy task. Attic and roof systems are complex system of framing, trusses, ducts, ventilation plenums, light fixtures, conduits and many other penetrations and terminations. Every penetration and duct must be sealed to prevent the flow of warm moisture laden air from living spaces into the roof system. This is a job for an expert.

Ductwork: In extreme climates all ductwork should remain in conditioned space however, due to design limitations, ductwork often must travel through non-conditioned attic space that needs to remain cold for a roof system to perform properly. To help minimize heatloss, ducts and vents must be completely sealed, insulated, and tested to eliminate leakage. It is vital that exhaust/ventilation fans originating in the house, such as stove and bathroom exhausts are ducted to the exterior and terminated in areas that will not cause snow on roofs to melt.

Access Panels: Access panels must be adequately insulated and have vapor seals to prevent warm moisture laden air from escaping into attic systems.

Light and Ceiling Fixtures: Recessed light fixtures in attic and roof systems are commonly poorly sealed and insulated creating a major path for air leakage. Ceiling mounted electrical devices such as lights and bathroom fans should be sealed at their boxes.

Chimney Chases and Plumbing Stacks: Large chases that run the entire length of a house are great paths for heat loss. They must be properly sealed to prevent this hot air from escaping into attic spaces.

Interior Partition Walls: Each stud bay can act as small chimneys directing warmth from the inside of the home through gaps at cap plates In all of these locations, All ceiling penetrations and top plate gaps must be sealed to prevent this heat transfer to the attic space.

Attic and Rake Walls: Radiation on a poorly insulated south facing attic wall can be sufficient enough to raise attic temperatures above freezing and accelerate ice damming. Typically attic walls are neglected and poorly insulated.

Beyond the Roof and Attic System: Interestingly heat loss and ice damming can be compounded by factors besides roof and attic insulation. Having poorly insulated walls and an unsealed crawlspace or foundation will create a powerful convective force called stack effect. The stack effect is the movement of air due to convection currents (warm air rising) within your home's building envelope. The greater the difference between the outside and indoor air temperature, the greater the air movement due to the stack effect. This will drive heat loss through the roof system and accelerate the formation of ice dams. As warm air exits the upper parts of the building, cold out- side air is sucked in at lower levels to replace it (infiltration). Occupants may complain of drafts, cold spots and other discomforts. The escaping warm, moist air condenses when it contacts colder surfaces in the building envelope, creating moisture build-up inside walls and building materials.

* With certain roof designs taking these precautions will minimize but not eliminate the conditions that lead to ice dams due to design limitations.

Additional Measures: Low Voltage Ice Melting Until recently, the traditional method of reducing ice dams has been to install self-regulating heat cable in a zig-zag pattern along the roof eave. This practice is extremely ineffective, particularly in very cold climates and in areas of heavy snow accumulation. Traditional "Zig-Zag" cables are not designed to clear the entire roof edge, especially under heavy winter conditions. "Zig-Zag" wire is not only ineffective, but it is also inefficient, costly to operate, and susceptible to damage from snow and ice buildup.

New low-voltage ice melting technology now exists that will effectively and efficiently clear away snow and ice from critical areas of the roof. These systems extend the life of a roof reduce the risks associated with snow and ice.

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