The ABC’s of Attic Ventilation
A proper roof ventilation system is important to the longevity of the roof structure as well as the shingles themselves. We like to think of a well performing roof system in terms of the ABC’s, which stands for:
“A” – Ample amount of ventilation (at least code required minimum ventilation)
“B” – Balanced ventilation between intake and exhaust
“C” – Control (control of moisture and air flow between the attic and occupied space)
A: Ample
We want to make sure there is an ample amount of ventilation so that air can flow freely between the soffits and the ridge vent. This creates a continuous flow of air that can move the warm, moist air trapped inside the attic and exhaust it through the ventilation at the ridge.
B: Balance
Now that we know there is ample room for the air to move within the attic, we need to make sure we have a balanced amount of intake and exhaust. A balanced system means there is an equal amount of intake and exhaust. This is usually achieved by calculating 25% of your intake needs on one side of your soffits, 25% on the other side of your soffits, and 50% for your ridge vent. A balanced system is achieved by ensuring there is unobstructed intake and clear continuous exhaust and that they are working in equal capacity. (Example: if only one side of your homes soffits are ventilated and you have a continuous ridge vent installed, the system is only 75% complete and will not effectively move all of the air in the attic.) In cases where there are no soffits to use for intake, we will install what is known as “intake vent.” This will create air intake on the roof deck itself as opposed to the soffits.
C: Control
Now that we have an ample and balanced amount of ventilation, we need to control the amount of warm, moist air being introduced into the attic space. Controlling moisture is done by ensuring things like bathroom vents are being vented through the roofs surface and not just into the attic space. Air-sealing penetrations in ceilings such as lights and ductwork can also help in controlling the amount of indoor air entering the attic.