Improper ventilation in an attic causes damage to the roof, allows water to damage the structure of the house, encourages the growth of mold and increases the cooling bill. For best protection, attic vents or vent fans should operate all year long.
When the sun strikes the roof and outside temperatures are hot, temperatures inside the attic increase the cooling load the air conditioner must handle. As these temperatures continue to increase, they bake the shingles and decrease their life expectancy.
When temperatures are cold, moisture that escapes from inside the house condenses on the cold roof and drips into the insulation. This encourages the growth of mold and mildew in the attic. The moisture encourages dry rot in the decking and rafters of the roof. With proper ventilation, this moisture escapes to the outside, preventing damage.
While many homes have gable vents, the cross ventilation they rely on does little to remove heat unless the prevailing winds happen to blow through them. Installing soffit ridge vents provides natural ventilation. The warm, moist air escapes from the ridge vents, while fresh air enters through the soffit vents. Ideally, homes should have 1 square foot of vent space for every 300 square feet of attic space, with the vents divided equally between the ridge and soffits.