A vented attic works where insulation is placed on an air sealed attic floor in hot/cold and mixed climates, when properly executed. The intent in cold climates is to maintain a cold roof temperature to prevent ice dams due to melting snow. In hot climates, to rid the attic of hot air to reduce the strain on cooling thus saving on energy costs. In mixed climates it will do the job of both.
The most common type of exhaust vents are ridge vents. They are installed where two roof planes come together (ridges). They are typically made of molded, sturdy polymer and are installed underneath a final layer of shingles to give a seamless look to the roof.
The box vent is installed over a hole cut into the roof, creating an opening for hot air and moisture to escape. They are both metal and hard plastic and are most effective when installed as close to the ridge line as possible.
Obviously, in the summer, the release of hot air from the home is important to help relieve the stress in cooling mechanics to conserve energy. But moisture release is also important in summer and winter. For extreme cold conditions, ice damming occurs when heat from inside your attic combines with heat from the sun to melt snow and ice on your warm roof. When water runs to the edge of the roof, it begins to refreeze. As the ice and water build up at the edges of your roof, it can back up behind and under the roofing materials, causing damage to your roof, your attic and even inside the walls of your home. Proper ventilation helps this warm air escape before it has a chance to melt the snow and ice on your roof. A well-vented roof is easy to see in the winter months. It still has snow on the roof, but not an icicle in sight.