South King County
Retaining Walls in Des Moines, WA
Quick answer
Des Moines walls are designed around the bluff and the view. We keep terraces low so the water stays visible from the deck, and we route every drain outlet away from the slope face rather than toward it. Landslide, erosion and shoreline mapping get checked on the parcel before a number exists.
The stratigraphy west of Marine View Drive explains most of what happens to walls here. It's the classic Vashon sequence: a dense till cap, advance outwash sand under that, Lawton Clay under that. Rain works down through the sand. It hits clay it can't pass and turns sideways at that contact. Wherever that groundwater daylights is where the bluff face moves. You can read the record in the leaning alders below Woodmont and Redondo. A garden wall doesn't get near that mechanism. It holds a few feet of graded soil. We'll tell you that straight instead of selling you block as slope stabilization.
On a Des Moines wall, the drain outlet is the biggest decision we make. Gather water up, run it at the top of a bluff, and you've done the worst thing you can do to a lot like this. So the perforated line goes inland to a controlled discharge. We don't point it downhill just because downhill is easy. Inside the mapped landslide, erosion or steep-slope hazard areas, a licensed geotechnical engineer comes in before we price anything. And any property within 200 feet of the ordinary high water mark falls under the city Shoreline Master Program.
The design brief here is unlike anywhere else. Half the reason people bought is the water, Maury Island, the Olympics behind it. So the instruction is keep everything low. Two 24-inch terraces with a planted bench between them beat one 5-foot wall on a view lot. They look better in February too, when the yard gets looked at from indoors. Techo-Bloc and Belgard units give you a finer face for that work. Salt narrows the planting on an exposed corner. Terraces get kinnikinnick, salal, hebe and lavender, not something that minds the wind. Access is the last variable. Plenty of the original 25-foot and 50-foot lots have one steep driveway and a street that won't hold a trailer all week.
What’s different about Des Moines
Everything west of Marine View Drive is bluff. What actually moves that ground is groundwater perching on Lawton Clay. So we route the wall drainage inland to a controlled discharge instead of daylighting it toward the slope. And we keep the design low. The view is the reason the yard exists.
Retaining Walls cost in Des Moines
| Item | Typical range | Unit |
|---|---|---|
| Segmental block gravity wall, under 4 ft exposedIncludes base, drain rock, fabric, perforated pipe and caps | $45-$70 | per face sq ft |
| Engineered block wall with geogrid, 4-8 ftExcludes engineering and permit fees, listed separately | $70-$115 | per face sq ft |
| Quarried basalt or granite boulder wallMachine access strongly affects the number | $60-$100 | per face sq ft |
| Natural stone veneer over reinforced core | $110-$180 | per face sq ft |
| Excavation, haul-off and structural backfillHigher on tight lots with no equipment access | $1,800-$6,000 | per project |
| Stamped structural engineeringUp to $10,000 where a geotechnical report or a steep-slope review is required | $1,600-$3,500 | per wall |
| Jurisdiction permit and plan reviewKent, Auburn, Renton and unincorporated King County all price this differently | $500-$2,000 | per permit |
These are typical installed ranges for the Puget Sound market in 2026, not a quote; the actual number comes out of a site walkthrough where we can see the grade, the soil, the access and where the water goes. You will find local bids starting nearer $25 per face square foot. That number is real, and it usually means no drain rock, no filter fabric and a base course laid on native soil — a wall that looks identical on day one and leans by year five. Our range starts where a full drainage assembly starts.
Permits in Des Moines
Permits go through City of Des Moines Planning, Building and Public Works. The standard Western Washington threshold applies. A retaining wall over 4 feet, measured from the bottom of the footing to the top of the wall, needs a building permit and stamped structural engineering. A surcharge can pull a shorter wall into review too. That means a driveway, a structure above, or a stacked tier. Des Moines adds two layers that matter more here than almost anywhere else we work. First, geologically hazardous areas. Landslide, erosion and steep-slope hazards are mapped along the marine bluff and the ravines. Grading, walls or significant excavation inside those areas or their buffers typically needs a report from a licensed geotechnical engineer on top of the structural work. Second, the Shoreline Management Act. Property within 200 feet of the ordinary high water mark of Puget Sound falls under the city Shoreline Master Program. There a patio, wall or grading project can require a shoreline exemption or a substantial development permit, and the review timeline stretches accordingly. Added hard surface can trigger stormwater review as well. These thresholds get revised, so we confirm with the city at permit time before we commit to a scope.
Retaining Walls in Des Moines: questions
Will a retaining wall stop my bluff from eroding?
No, and it's the most important thing we tell homeowners here. A block retaining wall holds a few feet of graded soil. A marine bluff failure is a much deeper movement. It's driven by groundwater perching on Lawton Clay, well below anything a garden wall reaches. Slope stabilization is a geotechnical design. Usually it comes down to intercepting water and redirecting it, and structure is the smaller part. We'll build the wall that makes your yard usable. We'll also tell you straight when the real problem is a geotech problem.
Is my wall inside the shoreline permit zone?
If any part of the work sits within 200 feet of the ordinary high water mark of Puget Sound, yes. The City of Des Moines Shoreline Master Program applies. That covers a good number of Woodmont, Redondo and Marine View Drive properties. Depending on the scope you may need a shoreline exemption or a substantial development permit. That review adds real time to the calendar. We measure the distance early, so the schedule we give you is the schedule you get.
Can you build terraces that keep my water view?
That's most of what we do here. Two low walls with a planted bench between them hold the same grade change as one tall wall. The difference is they stay under the sightline from the deck and the kitchen window. Seat walls get set around 18 inches. Planting gets picked to top out below the view instead of growing into it. One caution. Tiers stacked too close together can get reviewed as a single taller structure, so we work the offset out on paper first.
Can you work on a narrow platted lot with no street parking?
Yes, with planning. Plenty of the original 25-foot and 50-foot lots here have a single steep driveway and a street that can't hold a trailer for a week. We size the machine to the tightest side-yard pinch point. Pallet deliveries get phased so block isn't sitting on the street for days. Where a full-size excavator can't turn, we hand-carry. That adds labor, and you'll see it on the estimate instead of buried in a square-foot rate.