What is the appropriate ratio between free ventilation area and crawl space square footage for proper ventilation?

The appropriate ratio for free ventilation area to crawl space square footage is traditionally considered to be 1:150. This means that for every 150 square feet of crawl space, there should be one square foot of free ventilation area. This ratio is based on the need to ensure adequate airflow and moisture control in the crawl space, which helps to prevent structural damage, mold growth, and other moisture-related problems.

Having the correct ratio of ventilation is crucial for maintaining a healthy environment under the house. Proper ventilation allows the crawl space to be kept dry, which is essential for preventing pests, reducing humidity, and enhancing overall air quality in the living space above.

Other ratios, such as 1:100, 1:200, and 1:250, do not align with the commonly accepted standard for ventilation. These ratios may either offer too much or too little ventilation, leading to potential issues in moisture management, which is why the 1:150 ratio is considered the best practice.