Project guide
Fixing standing water with a French drain: what stone to use, how much, and the mistakes that clog one in a year.
Flat lots, heavy summer rain and a high water table mean South Florida yards hold water. The usual fix is a French drain, and the usual failure is the same one every time: the wrong stone, or no fabric, so the trench silts up and stops draining within a year or two.
#57 rock, washed. The washing is the whole point, because any fines in the stone migrate down and clog the voids the drain depends on. For a high-volume run taking roof and hardscape water, step up to ballast rock. You also need non-woven geotextile to wrap the trench and perforated pipe for the bottom.
A trench 60 ft long, 18 in wide and 24 in deep is 60 x 1.5 x 2 / 27 = 6.7 cu yd of stone. No compaction allowance, because the stone is placed loose. Order 7 cubic yards.
Dig to a consistent fall, at least an inch every eight feet, toward wherever the water is going. Line the trench with fabric, leaving plenty of overlap at the top. Two inches of stone, then the perforated pipe holes down, then stone to within three inches of the surface. Fold the fabric over the top, then cap with soil and sod. Never wrap the pipe in a sock and skip the trench fabric; the sock clogs first.
Materials for this job
Driveways, French drains, slab base and pipe bedding. The workhorse.
$37.50 / cu yd MaterialRoof ballast, construction entrances, heavy drainage and erosion control.
$37.50 / cu yd MaterialGrade changes, slab prep and lot levelling. Not for growing anything.
$11.25 / cu ydYard Drainage — common questions
Washed #57 rock. It has the void space to carry water and no fines to clog it. Unwashed or screened material will silt up and stop working.
Yes. Non-woven geotextile around the whole trench keeps surrounding soil out of the stone voids. It is the single biggest factor in whether a drain lasts twenty years or two.
Typically 18 to 24 inches, but fall matters more than depth. A shallow drain with consistent slope beats a deep one that is level.
Yes, and it should. Tie downspouts into solid pipe feeding the drain run, and size the trench up to ballast rock if you are taking a lot of roof area.
Pick your material, enter how many cubic yards and see the delivered number before you talk to anyone.