Crawl Space Inspections

D. Justin Reid, P.E.

D. Justin Reid, P.E.

Crawl Space Inspections

Financial losses can be avoided with periodic inspections of the crawl space under residential structures. Often times, a homeowner is unaware of issues in their crawl space until damages have progressed to the interior of the residence. Interior damages may consist of floors that are sinking or have become unlevel, flooring that has cracked or buckled, or cracks that have developed in the walls or ceilings. Often, the damage is the result of a moist crawl space, which can be avoided by a knowledgeable homeowner and periodic inspections.

Moist soil throughout a crawl space can result in foundation settlement, the result of the foundation walls and piers sinking. Settlement of the foundation places additional stresses on the floor-framing which can result in structural issues. Moist air throughout the crawl space may promote biological growth on the wood floor-framing. Wood with a moisture content exceeding 20 percent can result in biological infestation. Over time, biological growth attacks wood and can reduce its strength and stiffness which can also cause structural issues.

Common causes of moist conditions in a crawl space are related to improper construction. The International Residential Code (IRC) is the most widely accepted building code in the United States for single-family dwellings. Requirements in the code were established in order to prevent elevated moisture levels inside a crawl space. The code requires that the ground surface adjacent to the foundation should fall a minimum of six inches in the first ten feet, or five percent, to promote proper drainage. It is recommended that an approved vapor barrier be installed on top of the soil inside the crawl space to prevent ground moisture from entering the area under the home. When a vapor barrier is present, the code requires one square foot of ventilation for every 1,500 square foot of crawl space area. When vapor barriers are not present, the code requires one square foot of ventilation per 150 square foot of crawl space area. Ventilation is often provided by placing openings in the foundation walls that vent to the exterior.

Typically, the crawl space under a residence contains plumbing pipes and heating, ventilation, and air conditioning (HVAC) ductwork. Without periodic inspections of these items, leaks can go undetected. Plumbing leaks that are undetected can add a significant amount of moisture to and potentially flood the crawl space. Condensation can occur from ductwork that is not insulated in a proper manner or has become disconnected. Condensation can result in the floor-framing and decking becoming moist, causing issues like those previously discussed.  

In order to avoid costly damages associated with a moist crawl space, it is advantageous for the homeowner to ensure proper drainage adjacent to the crawl space, provide proper ground surface coverings and ventilation inside the crawl space, and conduct periodic inspections for leaks or condensation issues.


About the Author

D. Justin Reid, P.E. is a Consulting Engineer in our Birmingham, AL Office. Mr. Reid provides consultation related to evaluation of residential and commercial structures, post-fire structural evaluation, water intrusion investigations, and wind and hail damage assessment. You may contact him for your forensic engineering needs at jreid@edtengineers.com or (205) 838-1040.

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