What is the minimum attic venting required in an attic without a vapor barrier per one square foot of free space?

In an attic without a vapor barrier, the minimum recommended ventilation is generally one square foot of net free ventilating area for every 150 square feet of attic floor area. This is important because adequate ventilation helps to regulate temperature and moisture levels, preventing issues such as mold growth and wood rot.

When you are assessing the required ventilation for a given attic, it is essential to have sufficient air exchange to replace warm, moist air that can accumulate, especially in warmer months or climates. The ratio of 1:150 serves as a guideline for maintaining this balance, allowing for enough airflow to keep the attic space healthy and structurally sound.

The other choices reflect incorrect ratios for ventilation requirements. Each of these options suggests greater ratios of attic space per square foot of ventilation, which may not provide sufficient airflow for proper attic conditions, particularly in situations where no vapor barrier exists to mitigate moisture retention. Therefore, the recommended ratio of 1:150 is the most effective for an attic without a vapor barrier.