Rain Surface Water Drainage & Wet Basements and Moisture

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

To solve moisture and water problems in basements, before applying any insulation or sealer, you should install drain footings around the house and take into account the gutters and downspouts working.


Gutters and downspouts

Make sure that roof gutters (on your house's eaves) and the downspouts (that carry rainwater down from roof gutters) are working properly. They should be well cleared and opened: otherwise, rain water would sit on the roof and run down the walls damaging several elements of the house, including the house's foundation.

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


The house drainage elements

Surface rain water drainage control can be best achieved through:

- a sloped roof
- large overhangs
- sloped ground
- 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 can also be essential, mainly in rainy and snowy climates.


A Sloped Roof

Sloped roofs are particularly advantageous in terms of preventing moisture and its damages; flat roofs are bad options for controlling surface rain water drainage.

A large overhang

The exterior entries of the house should have sufficient overhang. A large overhang is essential to driven away rain and snow, and to avoid the large amounts of water and moisture collected around the bottom of the walls.

Sloped ground next to the house

The ground next to the house should slope away from the walls on all sides of the foundation for at least 10 feet. Concrete walkways, patios or driveways that slope toward the house should be revised. Rain water should be quickly driven away. This is a key element of a good surface drainage, and sometimes the most important, since it may be impossible to implement a sloped roof or a large overhang.

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


Creating an underground drainage system

Above-grade surface drainage may solve many problems of humidity and water infiltration in basements. But in many cases it’s also necessary to install an under-ground drainage system, which requires digging up the area around the foundation, which can be costly.

This under-ground house 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.

Other possible important measures


Grass in the perimeter of the house

Flower beds, bushes or trees and many elements of gardens should be removed from the proximities of the house walls and foundation. Instead of them, seed the area with grass (and install a sloped ground with an impervious clay layer and a concrete sidewalk around the house).

Curtain drains

Some experts propose excavating a trench alongside the house and filling it with gravel and a perforated PVC pipe. The goal is obviously stopping surface water from getting to the foundation.

Use dry wells to receive run-off

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..
 

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