Although a wet or damp basement may be a very discouraging condition, it can many times be solved easily and inexpensively. I have discussed a method to determine if ground water is the source of your problem on this site already. Refer to the referenced article on analyzing a water problem, and if you do indeed have a surface water issue, it can be fixed.
Things You Will NeedBackhoe and or Bulldozer
4" or 6" perforated drain tile
Step 1Ok, it has been determined that water drains to your foundation and or you have no place for your roof water to drain away. The first step is to place perforated drain tile around the perimeter of your foundation - about 12" to 24" out should suffice and about 24" deep. This will best be installed by a trained backhoe operator.
Step 2Place the filter fabric in the excavation and allow about 36" on of return on each side of the excavation. Then fill the excavation with about 6" of clean pea gravel. Install the perforated piping on top of the pea gravel and make all required connections, elbows tees etc. Fill Additional pea gravel to cover the top of the perforated tile by about 8" o 10". Now wrap the filter fabric from the side and over the top and make sure there is a healthy lap of fabric.
Step 3Connect the perforated tile to one or two or more outlets of solid pipe that will carry the water away to a low spot on your property. If you do not have a low spot you will need to install a drywell to hold and let the water drain away. A civil engineer can aid you in sizing this drywell as it is based on rainfall amounts and duration in your particular geographical area and how much impervious area you are draining away. Occasionally, I would install what we called a "French Drain" in a yard. This is an excavated area, like a small pond, filled with pea gravel and covered with filter fabric and top soil. This was the less expensive route.
Step 4Sometimes a much simpler remedy is to re-grade your yard to get the water to run away from the foundation and create a low spot or valley out from the house a distance, say 20 to 30' so the water can drain in the right direction. Additional make sure you have gutters and downspouts installed and lead the downspout extensions to this valley area as well.
Of course your first major rainstorm will test your system, but if installed properly you should have a dry basement which you can now convert to useful storage and additional living space.