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. This information will be used by contractors, homeowners, and diagnosticians to understand how ice dams occur and the relation to conditioned air infiltrating the attic zone.