A pitched metal roof generally needs ventilation to allow warm and humid air to escape from the attic space. A ridge vent is a sleek alternative to box vents, soffit vents, louvers or wind turbines.
The reasons for roof ventilation differ depending on the climate, but can be achieved with similar venting techniques in both cold and hot seasons. In cold climates, the reason for roof ventilation is twofold: firstly to expel moisture in the attic, and secondly to keep the roof cold. A cool roof temperature needs to be maintained to stop melting snow from sliding down the roof and forming ice damns. In hot climates, the primary purpose of ventilation is to remove warm air from the attic that has been heated by the sun.
Doing this reduces the building's requirement for cooling and subsequently lowers the strain on air-conditioning systems. In mixed climates, correct ventilation will provide both functions at different times of the year. A potential drawback to using a ridge vent, as opposed to another style of vent, is rain and snow entering the attic and causing rot. Alternatively, creating a completely unvented roof is an option, but generally only considered where snowfall is unlikely and humidity is very low.