We live in the Upper Peninsula (UP) of Michigan, nestled between a few of the largest bodies of fresh water in the world. We are graced with inordinate quantities of “lake effect” snowfall and typically receive 200-300” of snow every winter. Our latitude is above the 46th parallel and that guarantees temperatures that will keep our snow around through the winter, not fully melting some years until sometime in May. Snow loads on roofs can be enormous and our local codes require that new construction is rated for 90# per square foot “dead loading” to accommodate for this reality.
As a roofing contractor from the UP, I also must contend with common problem related to the snow that accumulates on rooftops. Ice buildup at the eaves or “Ice Damming” as it is commonly named, is the occurrence of large quantities of ice at the eaves and pooling water that ultimately causes leaking through the roof system and into the structure below.
Ice damming is caused by insufficient insulation and ventilation between the heated areas and the roof surface. The roof deck becomes warm enough to slowly melt the snow that sits on it and when that water drains to the cold eaves that extend beyond the heated area, it freezes. This process continues perpetually until the ice becomes a substantial dam, large enough to back water into the roof system itself.
When bidding a roof job, it is critical to identify and resolve the conditions that cause ice damming. If additional insulation and ventilation can be provided in an open attic area, that is an inexpensive fix. Often, however, sloped or cathedral ceilings make this type of upgrade impossible. In those situations additional insulation and ventilation must be applied over the existing roof deck. The insulation must be substantial and continuous to provide a full thermal break. I typically specify 3” of extruded polystyrene foam applied over the roof deck. The ventilation must also be continuous from eave to peak and must provide airflow through valleys and hips. I typically specify a 2×4 frame with 5/8” sheathing. Blocking off the old air venting is important as hydrostatic pressure will force moist air into soffits and ice will appear in those locations if this is not addressed.
Ice Damming is caused by a building issue that we can fix.