With all the rain today, I thought this article would be helpful...

Drainage is an efficient way to control rain water penetration through foundation walls and to prevent moisture and condensation problems in basements.

Gutters and downspouts

To solve moisture and water problems in basements, before waterproofing any walls or applying any insulation, you should install drain footings around the house and study the gutters and downspouts.

Make sure that roof gutters (on your house's eaves) and the downspouts are working properly. They should be well cleared and opened: otherwise, rain water would sit on the roof and run down the walls damaging the building and its foundations.

If possible and practical, add extenders (minimum 4 ft) and splash-blocks to drive the water away from the bottom of the residence.

Drainage control

Water drainage control can be achieved through...

- sloped roofs
- large overhangs and gutters
- sloped grounds
- curtain drains, dry-wells, grass (instead of flower beds or trees)

Creating an under-ground drainage system, involving the foundations and the footing of the house is also important in rainy and snowy climates.

A Sloped Roof

Sloped roofs are particularly advantageous to prevent moisture and its damages; flat roofs are bad options for controlling surface rain water drainage.

Large overhangs and gutters

Gutters and overhangs (3 feet overhangs aren't too much) drive rain and snow water away, avoiding accumulation of water and moisture around the bottom of the walls.

Sloped ground

The ground next to home should slope away from the walls on all sides of the foundations, for at least 10 feet. Concrete walkways, patios or driveways that slope toward the house should be rectified.

Driving the rain and snow water away, as quickly as possible, is crucial for a good surface drainage.

The sloped ground may involve a impervious clay layer and a concrete sidewalk, as shown in the image (source: University of Minnesota, Extension).

Creating an underground drainage system

Above-grade surface drainage is important to prevent moisture and water infiltration in basements, but it may be insufficient, mainly in rainy climates. In many cases it's also necessary to install an under-ground drainage system, which requires digging up the area around the foundation.

This under-ground drainage system is usually a combination of a gravel drainage layer with a drain tile (pipe) or perforated PVC pipe. Drain tile is usually placed on top of the footing. A minimum of 12 inches of cleaned gravel, crushed gravel, or crushed rock is placed around the drain tile, and close to the walls. Gravel is very important, and cheap, and will avoid many problems.

Other measures to avoid moisture in the foundation

Home perimeter

Flower beds, bushes or trees shouldn't be planted close to walls and foundations, and the water from sprinklers shouldn't touch the walls.

Curtain drains

You may dig a trench alongside the house - about 1-foot deep - and fill it with gravel and a perforated PVC pipe. The goal is to drive the surface water away.

Use dry wells to receive run-off

A dry-well is an underground structure that can receive the flow of water from rain, snow melt or other sources, dissipating it into the ground... This structure should be placed at least 12 feet from the house, and can involve a tank or a deep hole filled with gravel covered with landscape fabrics.

Creating a sump and installing a sump-pump

Sumps and sump-pumps relieve excessive water pressure in the bottom of the house foundation, and are relatively cheap to create and install. Combined with other measures, they may help solving the problem of damp basements.

Taken from: http://www.house-energy.com/Basements/Drainage.htm