If you have one, when was the last time that YOU entered, inspected, or had your crawl space professionally inspected?  

As a licensed home inspector for the State of Tennessee and an ASHI certified home inspector, I have seen a lot of damage in the under world that could have been avoided by performing annual maintenance inspections. The old adage, "Out of Sight - Out of Mind" doesn't work for this area of your property. What you don't know can cost you - thousands of dollars.

Water damage and water related issues are the number one issue that I find under houses. Loose toilets and leaks in waste lines at floor penetrations are issues that can go unnoticed for years. By the time you finally notice it; your property could have sustained thousands of dollars of damage!

Water damage does not always come from leaking pipes. Improperly installed or missing vapor retarders, can lead to water condensing on the sub-floor and framing members. Most vapor retarders consist of a sheet of plastic laid on the crawl space floor. 6mil poly generally meets the ASTM Standard E96-80 of 1.0 perm.

The term "vapor barrier", which is also commonly used, is somewhat misleading since it does not completely bar the transmission of water vapor. A vapor barrier is actually a vapor-resistant membrane, and is sometimes referred to as a "Moisture Barrier."

Water condensing against cooler flooring materials in bathrooms and kitchens can lead to mold growth. Keep in mind that once wood reaches 20% moisture content, fungus will grow. As of yet, there are no EPA regulations or standards for indoor mold contaminants. Likewise, there are no Threshold Limit Values (TLVs) for mold concentrations against which a room or building can be measured to determine if or to what extent humans have been exposed to molds in that building. People are exposed to molds in the natural environment on a daily basis, most without any adverse effect on their bodies. However; persons with compromised immune systems or asthmatics can have some adverse health issues in some properties. For more information on this subject, go to the Indoor Air Quality Association (IAQA) website.

As part of ongoing maintenance, it is strongly advised that you have your crawl space inspected annually. If this is an area where you do not want to venture, and I cannot blame you - for it is not my favorite place to go either, have a home inspector or other qualified person evaluate this neglected area. The little that it will cost can save you a lot in the end.