How do I determine what is the best ventilation for my roof?

Attic ventilation is an important part of roofing. Proper attic ventilation extends the life of a roof and reduces problems because it minimizes the temperature differential between the attic and the air outside. Proper ventilation will remove moisture and heat from the attic. Trapped heat and moisture can raise energy costs, cause ice dams, and damage roof system components as well as structural and personal items located inside the attic where temperatures can easily reach 150°F (65°C). Condensation that forms inside attics can be caused by the use of washing machines, dish washers, bath tubs, showers, and tumble driers unless these items are properly ventilated through the roof. In some cases the condensation can be bad enough to be mistaken for a roof leak.