Concrete Retaining Walls in Des Moines, WA

Retaining walls in Des Moines: what to know

The slope is the main fact. In March 2015 a slide behind homes on the 25000 block of 8th Avenue South left a ledge just under 200 feet above the beach and three houses unsafe to occupy. After the January 2006 slides, the city’s assistant engineer said Des Moines Memorial Drive sits on an old slide zone.

On slopes of 15 percent and more, the code limits how much ground can be disturbed and prefers a retaining wall that keeps a natural slope over a graded artificial one. Cut slopes cannot be steeper than 2 horizontal to 1 vertical without a soils report, so a deep wall excavation may need one.

Permits and rules in Des Moines

Planning, Building and Public Works treats a wall of 4 feet or less, measured from the bottom of the footing to the top, as exempt from a building permit when it supports no surcharge. A taller wall, or one carrying a driveway or building, needs a permit and engineered plans. Work in a hazard area must also be certified safe by an engineer or geologist with a Washington license. We check the wall height and the hazard mapping for your lot before quoting.

Rules change and vary by parcel, so we confirm the current requirements with the city before we start.

How we approach it

Check ravine, bluff, and landslide mapping before choosing a wall height
Keep cut slopes at 2 to 1 or flatter unless a soils report allows
Measure wall height at the footing, since the 4-foot permit line starts there
Send wall drain water to an outlet that adds no runoff to neighbors

For the full process, see our Retaining Walls page.

Building in the cold months? See our guide to winter concrete pours.

Our retaining walls work, serving Des Moines

Examples of our work. We build retaining walls in Des Moines and the cities around it. See all of our work

Questions from Des Moines homeowners

Is a 4-foot retaining wall in Des Moines exempt from a building permit?

Under the city’s handout, yes, if it measures 4 feet or less from the bottom of the footing to the top and carries no surcharge such as a driveway. Grading permits are separate, and walls in hazard areas get critical areas review. We confirm which applies.

My Des Moines yard slopes toward the Sound. Do I need a geotechnical report for a wall?

Possibly. Work in a bluff or ravine buffer or a landslide hazard area must be certified safe by an engineer or geologist with a Washington license, and the city can require special studies. A wall on gentler ground may not need one. The mapping tells us first.

Can I build a rockery or wall next to the street in Des Moines?

Inside the right-of-way, the roadside standards treat a wall or rockery over 6 inches high as a safety item, keep it out of the sidewalk, and set it back from the curb. Behind the right-of-way line, the building rules govern.