Adequate roof ventilation reduces cooling bills, extends shingle life, and prevents roof rot and ice dams in winter. Both roof and soffit vents are easy to install in just a few hours. They'll protect your house from expensive future repairs.
Ultimately a professional contractor can help determine exactly how much ventilation a home needs. As a rule of thumb, however, homeowners need one square foot of attic ventilation for every 300 square feet of ceiling space. Roof vents are commonly placed near the peak of the roof; soffit vents are placed in the eaves. Outside air can circulate in through the soffit vents and exit through the roof vents above. Homeowners can tell if their roof is acting like a sauna simply by touching their ceiling on a warm day. A hot ceiling indicates trouble and requires better ventilation.
The ideal attic should have an equal amount of air coming and heading out. Since heat rises, cool air can enter the attic from the eaves and remove hot air through the vents at the peak of the roof. While it may seem counterintuitive to tout home insulation and attic ventilation, it is crucial to have both for an energy-efficient home.