French Drain

Source: APCHQ

The establishment of a drainage system around the perimeter of the foundation is the first strategy to eliminate the problems of wet basement. NBC-MQ 9.14

The perimeter drains, commonly called French drains, must have a minimum diameter of 4 inches (100 mm) and be covered on the side and on top of at least 6 inches (150 mm) of crushed stone.

Moreover, the upper part of the drain must be below the underside of the slab basement. NBC-MQ 9.14.3.2.1) and 9.14.3.2.4).

This code requirement is, in the opinion of the APCHQ, illogical, because it allows the maintenance of a large amount of water under the slab. This is one of the causes of high humidity. It is therefore recommended to install the drain at the bottom of the soles.

In addition, drains water collected should lead to a drain, ditch or dry well. NBC-MQ 9.14.5.1.1

Detail of the installation of a French drain

Source: CNRC

Measures to improve drainage. In addition to the NBC-MQ, the following recommendations for the implementation of the drain should be followed:

• Remove the drain on a leveled at the base soles ground. If the ground is not level, it is best to sit on the drain layer 2 in. (50 mm) of gravel.
• Place the drain at a distance of about 2 inches (50 mm) of the sole. When the particles of the embankment are fine, they may be driven through the crushed stone and clog the drain. In this case, it is recommended to cover the crushed stone, not the drain, with a geotextile membrane.

If leveling the stone is made using a mini-tractor, it is likely that the thickness of crushed stone on the drain will not meet the requirements of the code. It is therefore necessary when the bitumen sealing is completed, raise the crushed rock with a shovel to thoroughly cover the drain gravel up to 6 inches (150 mm) above the sole.