It may be hard to believe, but what's going on in your roof could be what's causing the problems with moisture in your basement. Before you go digging yourself a French Drain around your foundation, it's time to look up!
Start With the Gutters
How long has it been since you've had the gutters cleaned? When gutters clog up, the water that is meant to be carried away by them will overfill and run down the side of your home and into your basement. Give your gutters the care they need – clean them out and inspect them for leaks.
After you are done cleaning the gutters, get a bucket of water or pull your hose to the roof. Dump the water on the roof and watch as it fills the gutter. Does the water flow in the direction of the downspout? If not, the slope on the gutter is not significant enough to keep the water flowing in the direction it needs to. The gutter will need to be repositioned raising the one end furthest away from the downspout.
Note: If you have lots of trees around your house, consider investing in gutter covers/guards. These are caps that cover much of the gutter to prevent debris from flowing into it, but not covering it to the point where the water will run over them.
Continue to the Downspouts
At the end of your gutters, you will see long pieces that connect the gutters to the ground below. Under the ground, there are pipes that carry the water from the downspouts, to your yard far enough away from the house to prevent it from seeping in through the basement walls.
If the drain pipes aren't extended far enough away from the structure, you can extend them. You will simply have to dig up the area where the drain pipe ends and purchase a connecting piece and some more piping. Dig a trench to set the pipe in, set it in place, connect the two and cover it back up making sure not to fill the end with soil.
Note: If the ground is frozen, you can disconnect the downspout from the existing drain pipe, connect it to a new piece and run the new drain pipe on top of the soil until it softens enough to dig.
If you are uncomfortable working on your gutters, talk with your local gutter professional to see if the gutters are the true cause of your damp basement.