There are three way we get moisture in our crawl space. One is from rain and poor drainage. Another way we get moisture is from some type of plumbing leak. This one is a little easier to fix. The third and potentially the toughest to remedy is atmospheric moisture. This is the type I was dealing with when I did the home inspection in Charlotte NC last week. Unfortuanately this condition had been going on for some time. You can tell if you look at the picture you can that the wood has actually gotten soft and shrunk down on the pier.
You want to keep the moisture level in the woood below 20% to keep it healthy from fungal activity and conducive for termites. If you notice in this picture it is 26% and have been so for many years. If you look closely you can see the fungal activity on the wood and the deflection. In addition to this the hardwoods above were buckeled. Usually the remedy to fix atmospheric moisture is more ventilation (crawl vents) and adding poly or plastic. This usually works well if you have smaller crawl and lots of vents. The problem is that if you have a larger home/crawl space with a garage (no vents adjacent to garage and patio or porch) and a patio or porch you are limited architectually on what you can do. This problem is even more compounded with AC ductwork running through the crawl. This will actually pull in more moisure via condensationmuch like having a cold drink on a hot day.
There is a solution to this delimea though. Traditional method of adding poly and vent fans won't work. You can have your crawl space sealed. In this process professionals actually come in and completey seal up your crawl space floor, walls, and crawl vents. They will then condition the space with a dehumidifier. Its like putting that cold drink in a refriderator. It will not sweat there because there is no atmospheric moisture here to pull from. If you decide to go this route I highly recommend getting a professional though because this is not really a DIY project. If your crawl isn't completely sealed up you will cause more harm than good because the moisture will still get in but you have made it even harder to get out. As a Charlotte home inspector I have seen the results of some DIY sealed crawl spaces and they aren't ptretty
In short have your crawl space checked for moisture and make sure it is below 20% If not get a professional to futher evaluate and figure out a course of action as you don't want to have to replace 50% of your joist because of rot not to mention the diminished indoor air quality from the mold like this house I inspected today.
Preston Sandlin of Home Inspection Carolina in Charlotte NC has been on HGTV My First Sale. He has also been interviewed by Fox News and is a regular on “Your Real Estate Today” on WBT radio program. He has also taught home inspection continuing education classes for realtors. He has been performing, teaching and consulting home inspections for over 15 years. Home Inspection Carolina has over 10 home inspectors and over a 100 years of combined experience in home inspection and construction. They perform home inspections, termite inspections, Radon testing, and infrared scanning in Charlotte, Gastonia, Waxhaw, Monroe, Matthews, Concord, Huntersville, Denver and many surrounding areas. Call Home Inspection Carolina and let them put their experience to work for you.