10/17/2026
ATTIC VENTILATION
In Louisiana (following the International Residential Code with Louisiana Amendments), you need approximately 0.0267 linear feet of ridge vent per square foot of attic space (the total square footage of home), under the standard 1:150 baseline ratio.
Let’s say a home is 3,000’ including the conditioned space, the porches, and the garage.
3,000 x .0267 = 80.1’ linear feet of PROPERLY installed ridge vent.
Most homes do not have 80’ of ridge. Be a geek like me today and notice how many homes have 10-15’ of ridge and that’s all the exhaust ventilation it has.
Inadequate attic ventilation traps extreme heat and moisture, which damages your roof, increases your utility bills, premature shingle aging, wood rot, ice dams in winter, voided roof warranties/insurance, and creates structural and health hazards (suspicious growth) throughout the home.
An effective attic ventilation system relies on a balanced 50/50 split between intake and exhaust airflow to remove trapped heat and moisture. Having slightly more attic intake ventilation than exhaust ventilation is acceptable and often preferred over having more exhaust.
Another method of measuring intake to achieve the 1 to 150 code is 3,000 sq.ft. divided by 2 = 1,500 square inches. Check the specifications of your type of intake. James Hardie vented soffit panels provide 5 square inches of net free ventilation per lineal foot, while VentedPlus panels provide 12.6 square inches of net free ventilation per lineal foot. On average, 1,500 sq. in. divided by 5 = 300’ of vented soffit. Good luck 🥴
A 12” whirlybird will handle up to 500’ when spinning. We should not mix whirlybirds (wind turbines) and ridge vents on the same roof. One exhaust vent can act as an intake for the other, disrupting the balanced upward flow of heat and moisture.
Note: Not all manufacturer specifications are the same. Calculations should be measured on the product to be installed on each individual building.
