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Read MoreAs we approach the cooler change of seasons, we look forward to many things; the stunning change of foliage, football, and atmospheric water vapor frozen into ice crystals and falling in light white flakes, more commonly known as snow.
If you live in the north, you’ve probably had anywhere from a few inches to several feet of snow at one time or another. Regardless of your location, if you have experienced snow accumulation along with freezing temperatures and certain building conditions, you may have been the recipient of an ice dam.
The term “ice dam” refers to the damming of water behind an accumulation of ice buildup along the eaves and/or valleys on a roof covered with snow. Heat loss from the home or building into the attic space or rafter cavities warms the roof deck and causes snow to melt. When this snowmelt reaches the eaves, it freezes as there is no heat loss in this area. This can lead to a buildup of ice and a backup of water, hence the term “ice dam”. See Figure 1 and 2 below for additional details.
This paper reviews the cause(s?) of ice dams, covers steps to prevent their formation, and discusses mitigation of damage when an ice dam forms. We will also review ANSI/IICRC standards to determine the categorization of water from ice dams.
There are a few key points that differentiate an ice dam condition from typical snow accumulation on a roof:
Ice dams are not as likely in early winter due to weather conditions that typically contain lower snowfall amounts and temperatures fluctuating between 20 and 30 degrees. In contrast, later winter months are more conducive for the conditions that result in an ice dam. One example occurred in February of 2010, when Pittsburgh, Pennsylvania received upwards of 24 inches of snow during a three-day period. The temperatures during that snow, and for two weeks afterward, stayed in the low 20’s to teens (can we just say below freezing?). As a result, numerous structures throughout the greater Pittsburgh area experienced ice dam issues.
Of course, geographically, weather conditions vary greatly and as a result the frequency and magnitude of ice dams will vary as well.
Obviously, since snow and colder temperatures are still regularly occurring weather conditions, the answer to preventing ice dams lies in good building design and building maintenance such as insulation inspection and OSB inspection.
Structures come in all shapes, sizes, and uses. For this paper, a typical wood-framed residential home will be used as the model for the discussion. The following are some contributing factors that increase the likelihood of ice dams as well as potential solutions.
Lack of Sufficient Insulation
Attics must be properly insulated to minimize the heat loss from inside the home to the attic space in the winter. The use of insulation greatly slows the heat loss, which is the reason building codes require certain R-values (the temperature difference between the warmer surface and colder surface of a barrier) based on geographic location. Colder areas typically require more insulation in the attic. The premise behind the insulation is to create a blanket in the attic to keep the heat inside the house and keep the cold air in the attic.
Additionally, air leaks and poor insulation can allow heat to quickly escape into the attic. Figure 1 above shows that the insulation does not extend over the exterior wall plates. This condition can allow heat to easily migrate into the attic, thus warming the roof sheeting.
Solution: Be sure the proper amount of insulation is installed so it does not allow for these conditions at roof/wall intersects and at ceiling penetrations (recessed lights, HVAC devices, etc.).
Lack of Adequate Attic Ventilation
By not having sufficient attic ventilation, warm air from inside the structure will migrate into the attic and become trapped, which then warms the underside of the roof sheeting. Like insulation requirements, the building codes also require ventilation of an attic space. The code requires one square feet of net free area per every 150 square feet of attic space (for example a 1500 square foot attic space will require a minimum of 10 square feet of net free ventilation). Ideally, 50 percent of the ventilation would be placed along the ridge of the roof and the remaining 50 percent would be installed along the eaves. This would give 5 square feet of intake air into the attic at the eaves and 5 square feet of exhaust at the ridge.
Solution: Properly installed and sized attic ventilation (soffit and ridge vents) will provide air flow that removes warm air from the attic before it accumulates.
Air Leakage
Similar to the lack of insulation, air leaks from the interior of the home also introduce warm air into the attic. A common location of air leaks is at pull down attic stairs or around light fixtures in the ceiling. Heat from the interior can quickly escape into the attic space at these areas.
Solution: Seal any penetrations into the attic space, insulate recessed light fixtures, caulk and/or foam around electrical, plumbing, or HVAC penetrations, and seal and insulate attic access doors.
Heat Sources in Attic Spaces
Any device that generates heat and is installed in the attic has the potential to warm the attic space and the roof sheeting. Furnaces are typically installed in the attic with poorly insulated supply ducts. Light fixture housings are also commonly installed in ceilings and the insulation is pulled away to facilitate installation (experts refer to heat movement as stack effect). These conditions can increase the heat in the attic space.
Solution: If possible, eliminate heat sources from the attic space. If there is an air handler or supply ducts in the attic, ensure that no air leakages exist at duct connections, and/or appliance covers (this is to include fowl and/or rodent damage). Then, insulate all ductwork for heating and exhaust devices. Duct connection is done by heating, ventilation, and air conditioning (HVAC) tape regardless of duct materials. Light fixture housings should be insulated (some fixtures become extremely hot and do not allow insulation to be in contact with the fixtures – replacing these hot light sources with LED or fluorescent lights can allow the fixtures to be properly insulated. Refer to the manufacturer’s requirements or contact a qualified electrician for these type of conditions).
Snow Thickness
At times, due to wind direction and intensity, it is possible that snow can be blown from the upper portion of the roof and expose or lift the shingles. Conversely, if snow catchers are installed at the base of the roof to hold back sliding snow, an accumulation of snow will occur at the base of the roof. When the roof is heated by solar radiation, the upper roof will warm faster, causing the snow to melt and flow down the roof slope. The lower roof, which is insulated by the snowpack, will not heat as quickly.
Solution: Removal of most of the snow from the roof surface is key, or at least reducing the thickness, will help prevent variants in the snow thickness and allow for even melting. Snow does not melt evenly; rather, it melts based on the energy that is applied to the snow. For instance, if a tree or another object is blocking the snowbank it will not melt evenly and will require extra attention from the owner and/or maintenance crew.
When water is entering through a ceiling of a residence (possibly from an ice dam), clients commonly ask about how to mitigate the resulting damage from an ice dam condition. Typically, snow will not “pour” into a building; rather, it will become absorbed or will collapse the roof with its weight. The solution to this problem is actually very simple – remove the water source. However, the execution of the solution can present some challenges and safety concerns during removal.
Removal of the water source, the snow, will eliminate the potential for the ice dam to grow and it will also eliminate the potential for water to back up under the roofing material and ultimately enter the structure. While easy in theory, the removal of snow from a steep, icy, and snow-covered roof is dangerous work. Professionals who are familiar with working in these conditions should be engaged. In addition to the dangerous conditions mentioned above, the weight of several feet of snow, combined with shovel-wielding workers bouncing on a roof, could lead to a sudden roof collapse.
If the means are not available to engage a professional service firm, a roof rake can be used by property owners. This tool can assist in the removal of snow from the roof while the operator stands safely on the ground. See Figure 3.
If the snow cannot be removed, what should be done? Let’s first discuss what not to do.
What should be done when experiencing water infiltration from an ice dam event and unable to remove the water source?
If the water intrusion is not minor, then a professional mitigation company may need to be contacted to provide dry-out of the wetted materials. If there is moisture intrusion, and weather permits, a roofing contractor should be contacted first, so they can identify and possibly eliminate the problem area. Then an appropriate mitigation contractor can be contacted.
As the contractor is often times the first onsite they will give a recommendation to a category of water from an ice dam event. Although not specifically defined in the current edition of the ANSI/IICRC S500, Standard and Reference Guide for Professional Water Damage Restoration, (S500), water from an ice dam that enters a structure could be placed into either of the three categories depending on the situation.
The categories of water, as defined by the current S500 document in Section 10.4.1, refer to the:
Restorers should consider the possibility that contamination has occurred. Contamination in this case is defined as the presence of undesired substances—the identity, location, and quantity of which are not reflective of a normal indoor environment—which can produce adverse health effects, cause damage to structures, systems, or contents, and/or adversely affect the operation or function of building systems.
Some say these categories are for human or animal (living) safety and health; however, they are in fact reflective of the build itself, its materials, assemblies, contents, and any products.
Category 1 Water
The S500 defines melting ice and snow as part of category 1. In theory, if the water does not contain any contaminants or additives that may be picked up while melting and/or being absorbed by building materials, then it could be classified as Category 1. These conditions would most likely not occur with an ice damming condition.
It is important to note that, if, for instance, a building’s supply line ruptures (which is Category 1) and the event affects asbestos materials that have to be removed, the situation is still considered a Category 1 with the presence of a regulated material.
Category 2 Water
The S500 does not discuss melting ice and snow in category 2. It states that category 2 “contains significant contamination and has the potential to cause discomfort or sickness if contacted or consumed by humans.” Because of the potential to contain contamination as the result of flowing through building materials, category 2 appears to be the best definition of water that enters a structure from an ice dam and does not contain a significant hazard.
To elaborate, snow and ice melt will move through the OSB pores where there exists wood and glue (glue is not porous). It then weeps onto the insulation, where it is absorbed, and often will stay in place due to felt paper (with alumina backing), preventing any further movement. If there is long term exposure to the intruding water, the insulation would eventually lose its ability to adsorb more water and allow for the moisture to flow to the drywall ceiling below. Drywall would then adsorb or absorb the moisture (it is porous); the water would then stay as the paper layer prevents it from moving further or allows it to become a stain. With enough weight accumulated, this water could cause the drywall ceiling to fail or collapse. Again, the water itself is not presenting the danger; rather, it is the structural materials. Therefore, intruding water should not be touched or ingested, and using PPE is recommended when handling these situations.
Category 3 Water
The S500 again does not discuss melting ice and snow in category 3. By definition, Category 3 water “is grossly contaminated and can contain pathogenic, toxigenic, or other harmful agents (fungi, bacteria, etc.) and can cause significant adverse reactions to humans if contacted or consumed.” It is important to note that this category only applies to the degree of biological contamination. In the definition of categories, the presence of regulated materials such as asbestos, lead, and even mold fall under a specific paragraph in the S500 that addresses those specific materials because they may require a specialized expert to test, remove, or sample.
Ice dams are a common issue for roofs in northern climates—most often occurring on eaves, though capable of occurring elsewhere—and they will continue to pose a challenge in terms of how to best manage the conditions that cause ice damming and/or fix the resulting damage.
Good building design, maintenance, and code compliance are good practices for ice dam prevention; however, since the weather plays a crucial role in the frequency and severity of ice dams, building owners may not always have the final say when dealing with an ice dam condition.
We would like to thank Dan Parker, John DiMenno, CR, CMRS, CMP, Rachel L. Adams, and Josh Woolen for providing insight and expertise that greatly assisted this research.
Dan Parker is a Vice President in J.S. Held’s Building Consulting Practice. He is a roof damage expert specializing in damage assessment and forensic analysis of all types of roof coverings. Dan’s experience includes forensic analysis of a wide range of industrial, multi-family, commercial, transportation, educational, governmental, and residential projects throughout the country. In addition to Dan’s roofing expertise, he has extensive experience with damage assessment involving other types of losses such as fire, water, theft, vandalism, flood, and earthquakes. His knowledge of damage assessment comes from hands-on experience during his tenure with some of the world’s most respected companies including DSI, Allstate, CNA and Haag Engineering just to name a few.
Dan can be reached at [email protected] or +1 470 287 3929.
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