Retaining Wall Drainage & French Drains

Retaining wall drainage keeps water from building up in the soil behind a wall, where it adds pressure and freezes in winter. Around Coeur d'Alene, spring snowmelt and rain make drainage the single most important part of a wall. The same builders often install French drains to move water away from foundations, walls and soggy parts of a yard.

How does wall drainage work?

Drainage stone. Clean crushed rock directly behind the wall lets water drop freely instead of pushing on the blocks.
Perforated pipe. A pipe at the base collects the water.
An outlet. The pipe has to discharge somewhere: to daylight downhill, or to a proper drainage system. A pipe with no outlet just stores water.
Filter fabric. Keeps fine soil from clogging the drain stone.
Surface grading. Directs runoff away from the top of the wall.

What are the signs of a drainage problem?

Water seeping through the wall face or joints
Staining or efflorescence on block
Ground staying wet behind or below the wall
Ice forming on the wall face in winter
The wall starting to lean after a wet spring

What is a French drain?

A French drain is a trench filled with drain rock and a perforated pipe that collects groundwater and surface water and carries it somewhere safer. It's used behind walls, along foundations and across wet areas of a yard. On sloped lots, a French drain uphill of a wall can intercept water before it reaches the wall.

Where can the water go?

Water has to discharge without harming neighbors or the street. On the Rathdrum Prairie, the ground drains fast and sits over the aquifer that supplies much of the area's drinking water, so drainage near fuel, chemicals or septic systems deserves extra care. Near lakes and streams, discharge and grading can fall under county shoreline and site disturbance rules.

What affects the cost of drainage work?

Existing wall or new construction. Retrofitting drainage behind a finished wall usually means excavating behind it.
Trench length and depth. Longer and deeper runs take more time and material.
Outlet distance. How far water must travel to discharge.
Obstacles. Landscaping, utilities, rock and hardscape in the way.

Prices come from the builder after they've seen the site. We don't quote prices ourselves, and a phone estimate is only a starting point for a wall.

Where we connect you with help

Common questions

Can drainage be added to an existing retaining wall?

Sometimes, by excavating behind the wall to add drain stone and pipe. If the wall is already leaning, a builder may recommend rebuilding that section with drainage.

Where should a French drain empty?

To daylight downhill, a dry well, or another approved outlet that doesn't send water onto a neighbor's property or a street. A builder can suggest options for your lot.

Related services

More background: Kootenai County retaining wall guide.

Retaining wall drainage and French drains