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Ice Dam Symptoms and Solutions for a Cold-Climate Roof Matt Dries Dr. Robert Seavey Assisted by Collin Coltman and Kristel Spiegelberg Sustainable Systems Management: Building Science and Technology University of Minnesota ________________________________________________________________ ABSTRACT Ice dams occur on cold climate roofs when warm zones on the roof melt snow, and cold spots simultaneously freeze the water into large ice formations, typically found on eaves. This is a result of improper air sealing and attic insulation, insufficient attic ventilation, and an assortment of design and construction flaws in new and old homes. Attic bypass in the winter relates to escaping heat from conditioned portions of the house into the attic as a result of an inadequate vapor and thermal barrier separating the two zones. Inadequate attic ventilation perpetuates ice dams by failing to cool the roof deck and venting moisture out. Non-vented warm and moist air can melt snow unevenly, and in extreme cases lead to frost in the attic. This fate causes a home durability issue, and can remain unfixed for years without proper diagnostics and solutions. This research will quantify and analyze attic bypass and air sealing effectiveness using zone pressure diagnostics and blower door testing on a South Minneapolis home. Contractors, homeowners, and diagnosticians to understand how ice dams occur and the relation to conditioned air infiltrating the attic zone will use this information. ________________________________________________________________ INTRODUCTION Ice dams occur on many homes annually and can incur major water damage repair costs to homeowners. This phenomenon is a result of melted snow on the roof that freezes over the eaves and blocks water from falling. Water will deteriorate shingles, sheathing, and wood rafters if it stands for long enough. Heat leakage from the house causes this snow to melt, but the moisture the heat leakage carries can be even more dangerous than the water from the melted snow. Heat leaks through penetrations in the pressure boundary separating the conditioned space of the house and its attic. The moisture from the house’s conditioned air condenses and freezes on cold surfaces in the attic at temperatures less than 32 degrees Fahrenheit. Attic frost occurs on wood rafters, wood sheathing, and the insulation in an attic. Mold forms in the attic when this frost melts, which is a significant indoor air quality issue for the house and its occupants. These problems are difficult to identify without adequate knowledge and resources to evaluate building performance. For the common homeowner, mold and ice dams may seem an annoyance brought upon by the extreme weather. However, these issues often point to areas of air leakage from the house. Homeowners should care about this because this points to significant energy loss as well as being harmful to the house. Energy loss on cold days increases energy bills. Older homes are more notorious for these leakages because of inadequate insulation and aging of materials, but penetrations in the air barrier between the attic and conditioned spaces occur in almost every home, old or new, in varying magnitudes. The homeowner cannot quantify this problem alone, and very often the problems can be undetectable without adequate tools such as an infrared camera and blower door. For this reason, a home energy auditor is recommended to inspect a house with attic or ice dam issues. It is important to understand why ice dams occur to better realize how the energy auditor can resolve these issues. The three core reasons for ice dams are: Inadequate insulation in attic, poor air sealing of the attic to house pressure boundary, and inadequate attic ventilation. Image 1 below depicts a basic ice dam and how it forms on a roof. Image 1: Formation of an Ice Dam on a Roof Image 1: Depicts how an ice dam is formed and the effects it can have on a house. Inadequate insulation Insulation prevents heat flow, but when the conditioned air inside the house is at a drastically warmer temperature than the air in the attic, then heat will leak faster. A proper amount of insulation must be added to the attic before other places because it can hold the most insulation and is the location of many harmful air leakage locations. Houses in MN built to the MN 2015 energy code are required to have R49 in the roof, so this would be a good goal for a homeowner to add. The current insulation value can be identified visually by determining the material and thickness of the layer of insulation in the house. The R-value can be determined with these measurements and by using the values given by Appendix 1. Ducts or other chase ways from the conditioned house must also be insulated to prevent heat leakage. Areas such as recessed lights may receive less insulation because of the space the box shaped fixture takes in the attic, so these areas must be well spray foamed. The end of an eave is also difficult to reach with insulation due to it being pinched between the rafter and joist. Attic hatches are another location where insulation is commonly neglected. Other areas commonly inadequately insulated are knee walls separating portions in an attic. Assessment of insulation levels should begin in these areas if ice dams are being investigated. Poor Air Sealing A pressure boundary in a house describes the theoretically airtight division between a conditioned and unconditioned space. This barrier should be aligned with the thermal boundary to negate the most heat leakage. Ducting in the attic greatly complicates the pressure boundary when placed outside of conditioned spaces. Commonly ducting and even HVAC equipment itself is placed in the attic. This is a problem when it is not properly air sealed and insulated because leaks in the ducts or equipment directly ejects warm, moist air into the attic. Bath fans and their ducts in the attic are another location where warm, moist air can leak into attic spaces. The pressure boundary is established at the attic by drywall or by a sheet of poly beneath the ceiling joists. Penetrations in the pressure boundary occur in gaps of the drywall, commonly for electrical or plumbing holes, recessed light boxes, and attic hatches. These areas are the culprit for air leakages, and some will be easier to identify and fix than others. An infrared camera used with a blower door test is the best way to identify air leakage. A process to measure the air sealing potential of the pressure boundary is discussed in the Methodology section. Air leakage in a house is measured and quantified using the blower door test, and the specific air leakage from the house to the attic is determined by applying zone pressure diagnostics to the blower door test. Inadequate Attic Ventilation Attic ventilation does not describe putting ducts and heating equipment in the attic, but refers to fans and vents placed along the roof deck, soffits, or gables. Attic ventilation combats the problems that be a result of improper insulation and inadequate attic air sealing. Cold air is naturally taken in from outside through the soffits and gables and released through openings towards the ridge of the roof. This keeps the roof deck cool, which prevents heat from the house from building up and melting snow on the house. Ventilation must be placed continuously among the soffits and must have sufficient openings towards the ridge. Opening up the house for outside air to flow seems to not make sense for energy efficiency, but it is necessary to prevent ice dams and attic frost. Intake should at least equal exhaust, but it is acceptable and sometimes favorable to have more openings by the soffit and less by the ridge. This will cause a positive pressure in the attic by allowing air to enter faster than exit. The theory behind this is that creating a positive pressure in the attic will reduce heat from escaping into the attic. If there is insufficient attic ventilation, than the roof deck will melt snow easier and will create a buildup of moisture in the attic. It is important to know that adding venting should take place after attic bypasses are sealed. Not doing this can lead to attic mold or frost. Baffles leading from the soffit to the ridge are very helpful in directing the air to flow passed layers of insulation and across the roof deck. Image 2 and 3 give simple depictions of recommended ventilation and baffles in an attic. Image 2: Example of a baffle in an attic to allow air ventilation passed insulation. http://www.diychatroom.com/attachments/f9/42924d1324578013-proper-vent-baffles-continuous-not-dsc04220.jpg Image 3: Pathway attic ventilation takes in a typical wall to eave assembly. Baffle is shown in this description as well. PURPOSE Ice dams are a complex phenomenon and often difficult to identify the underlying cause. Because the house acts as a system, there are many different possibilities for conditioned air to travel through the house and into the attic. The path of air leakage is often not straightforward and is constantly affected by the HVAC and other appliances that affect the pressure in different areas in the house. A snowmelt pattern was noticed among houses of the same house design. Dr. Robert Seavey owns one of such houses and wanted to understand what was causing this to happen, as a snow melt pattern such as this can indicate possible ice dam formation. A chase way was discovered to be underneath this part of the attic, but was thought to be sealed to the attic. Image 4 gives the snowmelt pattern that inspired the research.

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