During the month of January, I’ve been called to diagnose roof leaks on an almost daily basis. These leaks have a common characteristic – they show up when it’s cold. That usually signals that there is some form of accumulation of water on the roof, usually behind an ice dam, and that the waterproofing is insufficient to stop the water from forcing its way it. The existence of an ice-dam almost always means that there is excessive transfer of heat to the roof which melts the snow on the upper sections, and the resulting meltwater refreezes on the lower section over the soffits. To reduce this heat transfer, we rely on insulation (to reduce the amount of heat leaking into the attic) and ventilation (to dissipate the residual heat before it melts the snow on the roof). However, there is another player in this game, and it can cancel out the efforts at insulating and ventilating. That player is air leakage.