Hardscape drainage

Every hardscape has to answer one question: where does the water go? A patio sheds it across the surface and out. A retaining wall has to let it out of the soil it is holding back, or the soil gets heavier and pushes harder. Get either wrong and the structure moves — slowly at first, then all at once during a wet spring.

Retaining walls. Fixr's repair data names drainage issues first among failure causes: "water builds in the soil, putting pressure on the structure," making cracks and holes more likely. The fix is not a stronger block, it is a drainage path. Today's Homeowner's block wall guidance describes 4 to 6 inches of dense graded base gravel under the wall — about 8 inches for walls over 4 feet — compacted in 2 to 3 inch lifts, plus 4 to 6 inches of gravel behind each course to create a drainage zone, and perforated pipe at the base that daylights downhill for rainy climates or clay soil.

Flatwork. A patio or driveway needs positive slope away from the house and a base that drains rather than holding water. When it doesn't, water sits in the bedding layer, freezes, and lifts the surface. Fixr's patio repair data attributes uneven and sunken sections to water infiltration and describes sand layers weakening and pavers settling. Repair runs $3 to $15 per square foot for a sinking patio and $7 to $30 per square foot for paver repair.

Permeable systems are the deliberate version of drainage. EPA describes permeable pavement as letting rain and snowmelt seep through to soil and gravel below, reducing runoff, filtering some pollutants, and reducing the need for some conventional drainage features. That is a real engineering solution for a site with a runoff problem — but it needs a designed reservoir base, not just a different-looking paver.

Stormwater rules are local. Some jurisdictions restrict how much impervious surface you can add, or require that runoff be managed on your own lot. Those rules come from your city or county — call your local building or stormwater department before you finalize a design that adds a lot of hard surface.

How to choose

Ask where the water goes — out loud, on site

Make the contractor walk the yard and point. If the answer is vague, or ends at your neighbor's fence line, you have found a problem before it costs you money.

Insist on a gravel drainage zone behind any wall

Backfilling a retaining wall straight against soil is the classic shortcut. Gravel behind each course plus a drain pipe that exits downhill is the standard detail.

Confirm the slope away from the house

Flatwork against a foundation must fall away from it. A patio that drains toward your house turns a cosmetic project into a water intrusion problem.

Don't let drainage be an optional upgrade line

Fixr prices it at $2 to $10 per square foot of wall. It should be in the base bid. If it's presented as an add-on, the base bid is not a complete wall.

Check local stormwater rules before adding hard surface

Impervious surface limits and on-lot runoff requirements are set locally. Call your city or county building or stormwater department — do not rely on the contractor's memory.