Foundation vents are an important part of the crawlspace ventilation system in most homes with an unconditioned underfloor area. While these vents help to lower moisture levels in the crawlspace, they can also lead to significant moisture problems if not properly protected.
A common defect found at many homes are foundation vents or basement windows that are installed below the soil level, or below grade. When these vents or windows are below grade, they can allow water to flow through into the crawlspace or basement. This movement and pooling of water in a crawlspace or basement can lead to significant defects over time which can include:
Foundation and structural settlement
Wood destroying organism infestation (such as termites and carpenter ants)
Wood decay and dry rot
While this movement of water can cause significant defects, correcting the foundation vent or window problem can often be fixed with the use of foundation vent wells or window wells.
Foundation vent or window wells are often composed of concrete, metal, or pressure treated wood. These act as a barrier to prevent water from entering the foundation vent and passing through into the crawlspace or basement. Installing these wells is a relatively simple process, however orienting them properly is important in order to adequately protect the crawlspace or basement. Below is a video showing how to install a window well to prevent moisture intrusion into a basement:
While foundation vent or window wells can help to prevent water intrusion, negative or neutral grading around the home towards these vents or windows is often the most common root cause of water intrusion into the crawlspace or basement. Neutral grading is when the soil and landscape around the home is flat and not adequately sloped away from the foundation of the home. Negative grading is when the soil and landscape is sloped towards the home and foundation.
If the soil and landscape around the home are neutral or negatively graded towards the home, re-grading these areas is critical in order to prevent moisture intrusion in the home and crawlspace. Correcting improperly graded landscaping usually includes re-grading the soil around the home to be properly sloped away from the foundation. Ideally the ground should slope down 6 inches over 10 feet away from the home.
While there can be other causes for moisture intrusion, foundation vents or windows below grade, vents or windows missing wells, and negative and neutral grading towards the home are some of the most common reasons for moisture intrusion into crawlspaces and basements.