Operational Needs

• A lack of adequate attic ventilation can cause problems on several fronts. In the summer, excess heat (which rises naturally) moves from the rooms below into the attic. Without proper ventilation, the heat builds up and forms a thermal block of superheated air. This can lead to an increase in cooling costs, because the heat from the rooms below has no vertical escape.
  
  

Health and Physical Hazards

• In moist conditions, including during winter months, humidity and fluid can build up within an enclosed attic. This can lead to the growth of fungus and mold (a health hazard), speed the aging process for a roof, and warp wood materials in both the rafters and sheeting materials.
  
  

Improvement Implications

• Attic venting problems are often caused by upgrades or improvements to other areas of the home, such as an increase in insulation or the installation of replacement windows. These improvements alter the airflow within the home, resulting in an increase of moisture and condensation, which may manifest itself in moisture on windows.
  
  

Roofing Design and Venting

• Although ridge vents and power vents (attic fans) are both forms of home ventilation, they operate on different theories of air movement. The ridge vent relies on temperature and nature to regulate airflow, while the power vent uses an electric motor and fan blade combination to either draw air into the attic area from the home, or draw it to the outside from the attic.
  
  

Ridge Vent Design

• Ridge vents may be applied to roof gables or beneath soffits. They rely on weather change and natural airflow to moderate the temperature and humidity within an attic. They are most effective when used in areas with cathedral ceilings, as this design creates a rafter bay that has a much thinner profile. The rafter bay is like a small attic, and includes the amount of room between the ceiling of the room below and the base layer of the outside roof.
  
  

Power Vent Design

• Power vents, also called attic fans, operate on the same principle of air replacement as ridge vents. They use power and fan blades, however, to create a drawn airflow similar in concept to forced air heating or air-conditioning. Electricity is traditionally a source of power for this type of vent, although several designs also use solar power. Depending upon roof design, power vents are best for large, traditional attic spaces and may be used in tandem with ridge vents.