How deep should a French drain be?
French drain depth: About 8 inches to 2 feet deep should be sufficient for many water-diverting projects, though related systems, such as those built around foundations and sub-ground living spaces, as well as the bases of retaining walls, may be deeper.
Do French drains really work?
Properly constructed, french drains will work well to transmit water from the pipe to the exit of the pipe; however, they are not very efficient in dewatering poorly drained soils. Adequate fall means at least 2 ft lower per 100 ft of pipe or 0.25 in. per foot of slope.
What is the average cost to install a French drain?
The average cost to install French drains range from $2,800 to $6,500. Costs can be as low as $2,000 for a 100 linear foot drain in an exterior location to as high as $10,000 for a 100 linear foot perimeter drain.