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Your crawl space: Is It Dry?

Your crawl space: Is It Dry?


Construction of the living areas that are placed over crawl spaces, instead of basements, is a standard practice.  Ensuring that humidity and water are properly managed is necessary to ensure separation from the upper living (conditioned) area.

The single most common issue with crawl spaces are the impacts of long term damages associated with the failure to manage the moisture and temperature relationship within the space.  The crawl space must either become part of the conditioned space, or be constructed to create independence from the conditioned spaces.  Water sources, including the evaporation from the soil under the home, or standing water, can result in humidity levels that will allow uptake of moisture in the construction products, condensation, or the onset of biological growth.


Crawl Space Condensation found during a home inspection.

Crawl spaces should be inspected regularly to review the visible (and sometimes the non-visible) issues.  If active condensation is found (the formation of water droplets from the air’s humidity level coming to saturation – see image above), then many other issues have already occurred which require correction.  When found, the hope is that we found the condensation very early on in the process of damages, as long term degradation, corrosion, rot or biological impacts may already be at levels creating the need for more than just additional air exchange to remedy the situation.

The building codes prescriptive requirements for the ventilation of a crawl space can be discussed in two potential methods.  The first, passive ventilation, the second, active ventilation.  What the code fails to do, though, is to consider the actual layout of the property, and the impacts of on-site moisture generation.  The code anticipates that cross flow would be achieved from one end to the other, with no dead-air zones.  The code also considers that a loose-laid moisture retarder can reduce the need for ventilation by a factor of 100.

There are many reasons why passive ventilation will not achieve a properly conditioned, separated crawl space, including the layout of the home, the ground moisture condition, the direction and amplitude of the wind, and pressure differentials.  The second method, active ventilation, includes a provision for an amount of air exchange at 1 cubic foot per minute, per 50 square feet, when a vapor retarder is used.  The challenge with active solutions is the complexity of the systems, which involves laying out a number of intakes, exhausts, diffusers, and duct work to provide consistent air exchange throughout the space.

These systems are complex, and are more likely to require consultation with a building professional, who has the tools and experience to help with Solutions Before construction, or Solutions After a problem has been identified.


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