Poor attic ventilation can lead to mold growth. If you combine moisture with restricted air circulation you will create a humid and moist environment, the ideal environment for mold to grow and thrive.
Ventilation of the home attic is important for two reasons. During the summer, excess heat that builds up in the attic during the day results in high energy costs for cooling. Also, moisture produced within the home may move into the attic. If this moisture is not exhausted from the attic it can condense and cause insulation and construction materials to deteriorate. Thus, temperature and moisture control are the major reasons for providing attic ventilation.
The two common forms of ventilation used to vent an attic properly is the soffit vent and ridge vent. The soffit and ridge vent work together as a team to allow hot moist air to exit the attic.
Soffit Vent & Ridge Vent
A soffit vent is simply a vent installed on the underside of the eaves. The term used to describe the underside of the eaves is the soffit. The soffit vent permits fresh outside air to be drawn up into the attic. Think about attic ventilation as a two step process. Fresh air enters the attic through the soffit vents and exits through the ridge vent.
STEP 1 - Soffit vent - Air flow through the soffit vent.
Here is an up close image of the soffit on a home. The traditional soffit vents contain small holes that allow to enter. The small holes on a soffit vent looks similar to a cheese grater. Fresh air enters the soffit vent and makes its way into the attic.
The soffit runs around the perimeter of the home. If there is not a proper soffit vent installed then the ridge vent won't function. The soffit and ridge vents work together to move air from the bottom of the attic up through the peak.
STEP 2 - Ridge vent - Hot air rising through the ridge vent pulls more fresh air through the soffit vent.
Hot air naturally rises and exits out the ridge vent, pulling in fresh air from the soffit vents.
The ridge vent looks like a cap where the roof peaks. The cap allows air to exit the attic while still preventing rain or snow from entering the attic.