Homes that have a crawlspace have a unique set of concerns when compared to homes built on a slab, or on a basement foundation. Since a crawlspace is an enclosed space under the living space, problems can go unnoticed since most people will hardly ever, or never enter the crawlspace. Crawlspace issues that include water intrusion, plumbing leaks or other environmental issues, such as pest intrusion or wood destroying organism activity may continue for long periods of time, and are often only identified when a worker or inspector enters the crawlspace. In some cases, damage caused by long term problems could lead to significant expensive repairs. However, indoor air quality issues caused by mold, high moisture levels in the home, and pest excrement inside a crawlspace can sometimes be detected by home occupants if their health is impacted, or if odors become apparent.
One of the best ways to prevent mold growth and indoor air quality issues in the home, is to ensure that the surfaces between the crawlspace and home are properly sealed, and to ensure proper ventilation of the crawlspace. As a building science adage goes “seal tight, ventilate right”.
Current building standards require that the minimum net area of ventilation openings for vented crawlspaces shall not be less than 1 square foot per 1,500 square feet of under-floor space when there is a Class 1 vapor barrier installed. A crawlspace that does not have a vapor barrier installed shall not have no less than 1 square foot for each 150 square feet of under-floor space area. There should be a vent opening at least 3 feet from each foundation corner to ensure proper cross ventilation.
There are usually many penetrations between the crawlspace and home, such as where drain pipes, duct registers, and electrical chases are routed through floors, that can allow significant amounts of air to leak from a crawlspace into a home. Air sealing using spray foam, mastics and caulking can go a long way to help prevent unwanted air transfer from the dirty dusty crawlspace and the living space of the home.
In the case when additional ventilation is added to an under vented crawlspace, and air leaks between the crawlspace and the home are not sealed, the amount of airflow through the crawlspace into the home can increase. That’s why sealing penetrations between the home and crawlspace is a priority.
Check out the video below for more information about sealing floor penetrations: