Ridge vents and snow
Last fall, I roofed my home and installed the type of ridge venting that rolls out along the ridge. In December, with about 6 in. of snow on the roof, no sun and temperatures around 0°F, I noticed ice dams forming. In desperation I climbed onto the roof and removed the snow from all of the ridges, and the ice damming stopped. Since then, I’ve made four more trips onto the roof. The ridge-vent company told me that for optimum performance, the vent should be kept free of snow, a warning that was not included in the company’s literature. Is this true of all ridge vents, or should I install backup venting for the snowbound months?
Randy Rogers, Marquette, MI
Paul Fisette, director of building materials technology and management at the University of Massachusetts in Amherst, Mass., replies: It was astute of you to realize that a ridge vent clogged with snow can contribute to the formation of ice dams. While all ridge vents can become snowbound in very heavy snows, certain types of ridge vent are much better at keeping clear than others. Unfortunately, it sounds like you installed one that isn’t good at staying clear.
Ridge vents with external baffles are not only better at keeping clear of snow (drawing right) but they are also more efficient at exhausting air from the roof cavity. Like any ridge-venting system, baffled vents should be used in combination with continuous soffit vents. One manufacturer of baffled ridge vents, Air Vent Inc. (4801 N. Prospect Road, Peoria Heights, Ill. 61614; 800-247-8368), explains clearly in their literature that as wind passes over the baffles, negative pressure is created, drawing air from inside the roof cavity regardless of wind direction. Ridge vents without baffles at times will allow outside air to blow into the roof cavity.
Baffled ridge vents are also a lot less likely to let rain or snow into the roof cavity, and they are less likely than unbaffled vents to become covered by fallen snow. My advice would be to make one last trip onto your roof in warmer weather to remove your unbaffled ridge vent and replace it with the baffled variety.