Subsurface drainage · Foundation protection · Free inspection
French drain installation in San Antonio
A french drain is a gravel-filled trench with a perforated pipe at the bottom, wrapped in filter fabric and set with fall to a discharge point. Around a Central Texas foundation it has one job. It catches subsurface water so the clay at your slab edge stops cycling between soaked and bone dry, because that cycle is what moves foundations here. It will not lift a slab that has already settled, and we say so before quoting one. The free inspection maps where the water actually comes from, and about a third of our inspections end with no repair needed at all.
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The mechanism
What a french drain does for a foundation on expansive clay
Central Texas clay swells when it soaks and shrinks when it dries, and the foundation rides that movement. The damage does not come from the water itself. It comes from the difference, one stretch of the perimeter staying wet while another bakes dry, or the whole edge swinging between the two with the seasons. A french drain trims the wet end of that swing. Water moving through the ground hits the gravel, drops into the pipe, and leaves through the discharge instead of soaking the clay against your grade beam.
It is one tool among several, and it is rarely the first one we reach for. Most of the water that ends up against a slab started on the roof, so gutters, downspout extensions, and grading corrections usually come first and cost less. The french drain earns its trench when water keeps arriving below the surface after the cheap fixes are done, from a slope, a neighboring lot, or ground that simply holds water against the house.
The decision
When a french drain is the right fix
The signs that point at one are subsurface. A strip of yard that stays soggy days after rain. Water seeping at the slab edge or into a crawl space when everything on the surface looks fine. A flower bed against the house that never dries out. Those say water is moving through the ground itself, and a trench that intercepts it is the right scope.
Two situations get sold a french drain they do not need. Ponding after a storm is usually surface water, and grading or an area drain moves it for less money. And a slab that has already settled needs piers and a measured lift, because no drain lifts concrete. When the elevation survey shows real settlement, the drain is the thing that protects the repair, not the thing that replaces it.
Placement
How far from the foundation a french drain runs
There is no single distance, because the line follows the water. A drain protecting the slab edge runs tight along the grade beam, set below the depth the water reaches, so it relieves the ground touching the foundation. A drain cutting off water that arrives from a slope or a neighboring lot sits a few feet uphill of the wet zone and catches the flow before it gets to the house. Both need the same two things to work, real fall along the pipe and a discharge point lower than the pipe that actually takes the water away, whether that is daylight on a downhill grade or a pop-up emitter at the curb.
On the job
What installing a french drain involves
The digging is the visible part. The design decisions before it are what decide whether the drain still works in ten years.
Map the water first
Where it comes from, where it sits, and where it can legally and physically go. The free inspection covers this along with the floor elevations, so the drain gets designed against the actual problem instead of a guess.
Set the line and the fall
The trench route, the depth, and the slope of the pipe get set before anyone digs, because a drain without fall is a buried bathtub. The discharge point is chosen at this step, not discovered at the end.
Trench, fabric, pipe, gravel
The trench is cut, lined with filter fabric, and the perforated pipe goes in on a gravel bed with washed gravel around it. The fabric wraps closed over the top. That wrap is what keeps clay fines out of the gravel, and skipping it is the most common reason drains die young.
Give the water somewhere to go
Daylight on a downhill grade, a pop-up emitter, or an area drain tie-in. The discharge gets tested with water before anything is buried, because this is the part you cannot see failing later.
Restore the surface and re-check
Backfill, grade, and sod or rock over the run, sloped so surface water still sheds away from the house. You get the readings and photos of what went in the ground before it was covered.
Costs
What drives a french drain price
Length and depth of the trench set the base, because both are dirt moved by hand or machine. The discharge route moves the number more than people expect, since a run that can daylight downhill is simpler than one that has to travel to the street. Access matters, fences, tree roots, tight side yards, and any flatwork that has to be cut and repaired. So does what goes back on top, rock is cheaper to restore than sod, and sod is cheaper than a paver path. Drainage work here is scoped line by line and priced as its own line item, so you can see what each part costs next to any other work the readings call for. The inspection is free and the quote is written and itemized.
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Straight answers
Common questions about french drains
Related pages
Where to read more on this site
Water sitting where it should not?
Free inspection, written readings, and a straight answer about whether the fix is a drain, a downspout, or nothing at all. We trace where the water comes from before anyone talks trenches.
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