Balanced System

The Key to Proper Attic Ventilation
The most important factor in roof ventilation is the need for a "balanced system". This means for every inch of air exhausted, it must be balanced by providing the same or greater amount of air intake at the eaves.

Providing a balanced system assures that damaging heat and moisture is being vented out of the attic, protecting the roof from premature deterioration, costly repairs and wasted utility dollars. If an attic has a properly balanced system, the airflow will move from the bottom of the attic to the top, pushing out heat and moisture in a natural flow using air pressure, thermal effect and diffusion.

If the Net Free Area (NFA) at the ridge is higher than at the eave, a reverse airflow can occur. In an unbalanced system the airflow can come from the top of the house and push down toward the eaves. As a result, heat and moisture are not allowed to escape and additional air and moisture can be drawn into the home that is why it is important to have a balanced system.

Recognized by builders throughout the industry, is the FHA standard for static ventilation, as found in HUD requirements for proper ventilation. These requirements call for a ratio of 1:300. This means one square foot of ventilation for every 300 square feet of attic. In addition, specifications for good attic ventilation require a balanced system - at least 50% of the vents at the eave and 50% at the upper portion of the roof. (In cases where a 50:50 balance cannot be achieved, always provide more than 50% of the ventilation at the eave).

When used with the correct combination of soffit vents, Trimline® Ridge Vents offer an efficient means to achieve a balanced ventilation system.