Fix the drainage before you build the patio

Some signs show up only in a storm. Others you can spot on a dry afternoon.

• Puddles that are still there a day after the rain stops
• Water that runs toward the house instead of away from it
• Low spots on the old patio or walkway, often by the back door
• Gutters that overflow, or downspouts that empty at the base of the wall
• Soil and mulch that wash out of the beds or down the slope
• A side yard that stays soggy for days
• Water that comes over from a neighbor's yard, or runs into theirs
• Pavers that have sunk near the house, or a concrete crack with one side higher than the other

If you've seen even one of these, it's worth dealing with before anything new goes on top.

A patio is only as good as the ground under it. Pavers or concrete sit on a packed gravel base, and the base sits on soil. When water keeps getting under the base, the soil softens and the base can shift. Pavers can sink in the low spots. Concrete can crack, and one side can end up higher than the other.

The slope matters just as much. A new patio usually runs right up to the house. If it tips even a little toward the back door, rain runs toward the wall instead of away from it.

Then there's timing. A drain line under the patio is simple to lay before the base goes in. Adding one later usually means cutting into the new patio.

Water always wins. If it has nowhere to go, it sits by the house. So a drainage plan answers two questions: how the water gets away from the house, and where it ends up.

• In the City of LA, draining to the street through the curb needs a permit from the Bureau of Engineering.
• Since April 2024, most small projects in the City of LA no longer trigger the City's low impact development (LID) stormwater rules. Adding or replacing a large paved area in some environmentally sensitive areas can.
• In the City of LA, LADWP doesn't allow sprinkler water to run off into the street. Other water providers set their own rules. We plan drainage and sprinklers together.
• In unincorporated LA County and in other cities, local rules decide what can drain to the street. Some cities, like Calabasas, also review paving or grading that changes the way water drains across a lot.
• In the Conejo Valley, Thousand Oaks and Newbury Park follow City of Thousand Oaks rules. Oak Park is in unincorporated Ventura County, so county rules apply there.

On a backyard project, the work usually goes in this order.

1. Walls. Most of what holds a retaining wall up is out of sight: the footing, the gravel behind it and a path for water to get out. That path ties into the yard's drainage.
2. Surfaces. Next comes the patio: the dig, the packed base, the slope and the edges, and last the pavers or the concrete. Artificial grass goes in at this stage too, on a base that drains. Channel drains go into the surface wherever water would collect.
3. Planting. Plants and irrigation go in last, so nothing new gets dug up.

Can a French drain go under pavers? A French drain is a gravel trench with a perforated pipe at the bottom. It collects water that soaks into the soil. It can run under a patio, as long as it goes in before the base and leads to an allowed outlet. Puddles on top of the patio are a different problem, and usually come down to slope or a surface drain.

You don't have to do it all at once. If you build in phases, the drainage still goes in first, and the patio can follow when you're ready.

On a dry day, we read the yard from the slope, the low spots and the downspouts. In a storm, the water shows you where it goes.

A drainage plan can move water away from the house and the places you use. It can't change how much rain falls, and on its own it can't control water coming from higher up the hill or from a neighbor's yard. We'll tell you plainly what a fix can and can't do. The goal is to let the dog out after rain without muddy paws coming back in.