Proper attic ventilation is the lungs of your home. It extends the life of your shingles, lowers cooling bills, and prevents ice dams. The goal is “Balanced Airflow”: Intake at the bottom (Soffits) and Exhaust at the top.
1. The 1/150 Rule (Building Code)
Most building codes follow the 1/150 rule: You need 1 square foot of net free vent area (NFVA) for every 150 square feet of attic floor space.
2. Exhaust Types: Ridge vs. Box
You must choose ONE system. Mixing them short-circuits the airflow.
| Type | Pros | Cons |
|---|---|---|
| Ridge Vent (Continuous) | Most efficient. Installed along the entire peak for uniform airflow. Looks best (invisible from street). | Cannot be used on Hip roofs with very short ridges. |
| Box Vents (Turtles) | Easy to install. Good for complex roof shapes. | Less efficient (creates “hot spots” between vents). Prone to leaking if not flashed properly. |
[Image of ice dam diagram]
3. The Intake Problem
The most common failure we see in inspection reports is Blocked Intake. Even the best Ridge Vent won’t work if the Soffit Vents are painted over or blocked by insulation. Your roof needs to “inhale” cool air at the bottom to “exhale” hot air at the top.