The simple answer to the question of how many roof vents you need is: it depends on the square footage of your attic. Vents are a crucial part of maintaining a healthy attic, roofing system and home. In many places, they are required to be installed as part of local building codes.
There are two basic functions of vents: air intake and exhaust. And their primary function is to keep air circulating in your attic.
The Benefits of Roofing Ventilation
By allowing for the circulation of air in your attic, proper ventilation offers a number of advantages.
- Prevents moisture buildup in the attic and the mould and mildew growth it can cause
- Helps prevent ice dams from forming in the winter
- Moderated temperatures in the attic, which can increase energy efficiency in the rest of the home, lowering heating and cooling costs.
Types of Roof Vents
As we said, there are intake vents and exhaust vents. Toronto roofing companies determine which are intake and exhaust vents by their placement on the roof. As hot air naturally rises, vents at the lower edge of the roof are the intake vents, and those higher up on the roof at the peak are exhaust vents. Some examples of vents are:
- Soffit Vents – Most often the intake vents on the roof, soffit vents are located on the soffit of the roof which is the underside of the overhang of a roof.
- Gable Vents – Named for their location on roofing gables (sides of house).
- Turbine Vents – Placed higher up on a roof’s surface, turbine vents use a wind-powered turbine to suck the hot air out of the roof.
- Ridge Vents – Ridge vents run along the peak of the roof, making them an ideal exhaust vent
How to Determine How Many Vents You Need
The rule of thumb used to determine the number of roof vents to install is one for every 300 square feet of attic area if your attic has a vapour barrier, and one for every 150 square feet of attic area if the attic does not have a vapour barrier.
Vents are rated by their net free area (NFA), which is the amount of space the vent has for air to flow in or out. The total NFA of the roof vents you need should be split 50/50 between intake and exhaust.
That rule can change if the slope of your roof is more than the average 6:12 slope (a rise of six feet for a run of 12 feet) because there will be more space, heat and moisture to ventilate in the attic.
If you liked this post, check out our recent article about the best roofing materials for the Canadian climate.