I’ve put more money into moving water around our property than into the concrete itself, and if I’d understood that going in, I’d have spent it in a different order. Our first project after buying the house was a patio repair. It failed again within three years because nobody, including me, had asked where the water upslope of it was actually going. The second time around we fixed the grading first, and that patio has been fine for over a decade since.
Grading is cheaper than almost anything else you can do
Most of what goes wrong with flatwork and foundations on these hillside lots traces back to water sitting somewhere it shouldn’t, and the cheapest way to prevent that is getting the ground to shed water away from a structure before it ever reaches a drain, a swale, or a slab edge. A slope of even 2 percent moving away from a foundation for the first several feet makes an enormous difference over the life of a house, and it costs nothing but dirt and a rented compactor if it’s done during a regrade rather than added later. On a lot in Dunbar where I helped a neighbor sort out a wet crawlspace, regrading the yard so it actually fell away from the house solved most of the problem before we ever talked about drains.
Swales, and why they’re not just a ditch
A swale is a shallow, broad, grassed or stone-lined channel that carries surface water across a yard without the erosion a narrow ditch would cause, and getting the shape right matters more than most people expect. Too narrow and steep, and it erodes or channels water hard enough to undercut whatever it crosses; too shallow and flat, and it becomes a wet strip of lawn that goes nowhere. A cutoff swale set across a slope above a driveway, patio, or foundation intercepts water running downhill before it reaches whatever you’re protecting, a much easier problem than managing that same water after it’s already crossed the thing you didn’t want it on. Sizing a swale for what it needs to carry in a real storm, rather than guessing at a shape that looks about right, is where I bring in someone who can run those numbers properly.
When a trench drain earns its cost
A trench drain, a narrow channel with a grate set flush into the surface, makes sense where a swale can’t do the job: across a driveway or walkway you still need to drive or walk over, or at the base of a slope where water arrives with more volume than an open channel can handle gracefully. They’re not cheap to install correctly, since they need their own outlet piping rather than an open discharge a few feet away, but on a driveway with real grade behind it, a trench drain at the top has saved us from resurfacing the lower section more than once. Where a swale can do the job, it’s almost always the better first choice.
Where the water is actually allowed to go
Every pipe, swale, or trench drain has to end somewhere, and it’s tempting to just aim it at the nearest low spot and move on. That low spot is often a neighbor’s yard, a public right of way, or a drainage easement with its own rules about what can be discharged there. Dumping concentrated runoff onto a downhill neighbor’s property, even unintentionally, creates a dispute that outlasts the original problem, and routing it into a storm system not designed for it can create issues past your own lot line. Before finishing any drainage project, a call to the city or county to confirm the discharge point is actually legal, not just convenient, is worth making.
Maintenance is the part everyone skips
Nearly every drainage failure I’ve dealt with, or helped a neighbor sort through, traces back to something that used to work fine and got clogged: leaves packed into a swale inlet, a downspout extension knocked loose or buried under mulch, a trench drain grate full of gravel nobody cleaned out in years. A downspout dumping water two feet from the foundation instead of ten or fifteen feet away undoes most of the benefit of good grading, and it’s usually a five-dollar extension pipe that’s the whole fix. Walking the property after a hard rain, watching where water actually goes rather than where you graded it to go, catches most problems before they become a cracked slab or a wet crawlspace. FEMA’s guidance on stormwater and flood risk is worth reading, at the Federal Emergency Management Agency’s site. For when drainage fails badly enough that water gets under a slab rather than around it, see this piece on flood water and what it leaves under a slab.
Frequently asked questions
What’s the difference between a swale and a trench drain? A swale is an open, shallow channel that carries surface water across a yard, while a trench drain is a covered channel with a grate set into a hard surface like a driveway where an open channel isn’t practical.
How far should a downspout extension carry water from the house? Roughly ten to fifteen feet away from the foundation is a common guideline, since water discharged just a foot or two away tends to soak right back toward the same ground the foundation sits on.
Is it legal to drain water onto a neighbor’s property? Generally no, and even where it isn’t strictly prohibited it’s a common source of disputes; checking with the local city or county about legal discharge points before finishing a drainage project is worth the phone call.