Attic ventilation works on the principle of natural air circulation. Fresh air enters through the soffits (under the eaves) and warm, humid air escapes through ridge vents or roof vents, creating a continuous flow that removes moisture and regulates temperature.
Basic Operation
Air Intake
Fresh, dry air enters the attic through the soffits, located under the roof eaves. These openings allow outside air to enter the attic space.
Air Circulation
Air naturally warms up in the attic, whether from the sun's heat on the roof in summer or from heat rising from the house in winter. Warm air, being lighter, naturally rises toward the top of the roof.
Air Exhaust
Warm, humid air escapes through vents located at the top of the roof (ridge, roof vents, turbines). This exhaust creates a draft that continuously draws fresh air through the soffits.
Types of Ventilation Systems
Passive Ventilation
The most common system uses only natural convection (warm air rises). It requires no energy and operates continuously. This is the most widespread system in Quebec homes.
Active Ventilation
Some installations use electric fans or wind turbines to accelerate air movement. These systems are useful in situations where passive ventilation is insufficient.
System Components
Vented Soffits
Soffits are the panels installed under the eaves. Vented soffits are perforated or have grilles that allow air to enter the attic while keeping insects and debris out.
Ridge Vents
Installed along the roof peak, ridge vents are extremely effective because they are positioned exactly where warm air naturally accumulates.
Roof Vents
These vents are installed on the roof slope, usually near the top. They allow warm air to escape and are available in various styles.
Baffles
Baffles are installed in soffit cavities to ensure attic insulation doesn't block the air passage from the soffits to the ventilated space.
System Balance
An effective ventilation system requires a balance between air intake and exhaust. The general rule is to have 1 square foot of net ventilation for every 150 square feet of ceiling area, equally divided between soffits and roof vents.