What is building code's recommendation for venting an attic or crawlspace without a vapor barrier?

The recommendation for venting an attic or crawlspace without a vapor barrier is one square foot of vent for every 150 square feet of the space. This guideline is established to ensure adequate airflow, which is critical for maintaining proper moisture levels and preventing issues like mold growth and wood rot.

By providing sufficient venting, you allow warm, humid air to escape from the attic or crawlspace, helping to maintain a balanced environment. This is especially important in areas with fluctuating temperatures and humidity levels, where trapped moisture can lead to significant structural and indoor air quality problems.

The specific ratio of one square foot of vent per 150 square feet of space reflects building science principles that take into account the need for effective ventilation while avoiding over-ventilation, which can also create problems by allowing too much cold air to enter and potentially lead to energy loss or increased heating needs. Thus, following this ratio helps to harmonize energy efficiency and moisture control.