How to Vent a Crawl Space in an Old House

Moisture in your crawl space can damage your hardwood floors.

More than the other rooms in your house, it is essential that you ventilate your attic and crawl space. Without proper ventilation in your crawl space, mold, mildew and bacteria will grow. Moreover, moisture, chemical vapors and radon may migrate into your home. Fortunately, in your old house, or in a newer house that has a crawl space, you can ensure that the crawl space is properly ventilated.

Things You'll Need

• Standard metal foundation vents
• Vapor barrier

Instructions

1. Install standard metal foundation vents that measure 8 by 16 inches in each corner of the crawl space. Be sure that the vents are installed within the top 8 inches of the foundation wall. This will help create good air flow across the entire crawl space.

2. Install standard metal foundation vents evenly along the foundation wall between the corner vents. Note that standard building codes require 1 square foot of ventilation per 150 square feet of crawl space.

3. Open the metal shutters, if included, on each vent. These shutters should remain open year round with the exception of the very coldest days.

4. Spread a vapor barrier across the floor of your crawl space. The vapor barrier should be made of a material with a permeability value of less than 1.0. If you have wooden floors inside your home, the vapor barrier should only cover two-thirds of the crawl space floor to prevent the wood floors from drying out. The vapor barrier is designed to prevent ground moisture from rising up into the crawl space and into your home. While not considered ventilation, a vapor barrier helps the performance of your ventilation.

References

• University of Georgia: Moisture Control in Homes
• Smart Vent: Crawl Space Moisture Control