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 is the classic Vashon sequence: a dense till cap over advance outwash sand over Lawton Clay. Rain moves down through the sand, hits clay it cannot pass, and comes out sideways at that contact. The elevation where that groundwater daylights is where the bluff face moves, and you can read the record in the leaning alders below Woodmont and Redondo. A garden wall does not reach anywhere near that mechanism. It holds a few feet of graded soil, and we say so plainly rather than selling block as slope stabilization.
Practically, the drain outlet is the most consequential decision on a Des Moines wall. Concentrating water and running it toward the top of a bluff is the worst thing you can do to a lot like this, so the perforated line gets routed inland to a controlled discharge rather than pointed downhill because downhill is convenient. Inside the mapped landslide, erosion or steep-slope hazard areas a licensed geotechnical engineer joins before we price anything, and 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 and the Olympics behind it, so the instruction is to keep everything low. Two 24-inch terraces with a planted bench between them beat one 5-foot wall on a view lot, and they read better in February when the yard is looked at from indoors. Techo-Bloc and Belgard units give a finer face for that work. Salt narrows the planting on exposed corners, so terraces get kinnikinnick, salal, hebe and lavender rather than anything that resents wind. Access is the last variable. Many of the original 25-foot and 50-foot lots have one steep driveway and a street that will not hold a trailer all week.
What’s different about Des Moines
Everything west of Marine View Drive is bluff, and groundwater perching on Lawton Clay is what actually moves that ground. So the wall drainage gets routed inland to a controlled discharge instead of daylighting toward the slope, and the design stays low because 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 |
| Structural engineering plus jurisdiction permit | $1,600-$4,200 | per wall |
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.
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, and a surcharge from a driveway, a structure above or a stacked tier can pull a shorter wall into review. 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, and grading, walls or significant excavation inside those areas or their buffers typically require 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, where 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 also trigger stormwater review. These thresholds get revised, so we confirm with the city at permit time before committing to a scope.
Retaining Walls in Des Moines: questions
Will a retaining wall stop my bluff from eroding?
No, and this is 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 driven by groundwater perching on Lawton Clay well below anything a garden wall reaches. Slope stabilization is a geotechnical design, and it usually turns on intercepting and redirecting water rather than on structure. We will build the wall that makes your yard usable and tell you honestly 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, and 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, and the review adds real time to the calendar. We measure the distance early so the schedule you are given is the schedule you get.
Can you build terraces that keep my water view?
That is most of what we do here. Two low walls with a planted bench between them hold the same grade change as one tall wall while staying under the sightline from the deck and the kitchen window. Seat walls get set around 18 inches. Planting is chosen to top out below the view rather than grow into it. One caution: tiers stacked too close can be reviewed as a single taller structure, so the offset is a design decision, not an afterthought.
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 cannot hold a trailer for a week. We size the machine to the tightest side-yard pinch point, phase pallet deliveries so block is not sitting on the street for days, and hand-carry where a full-size excavator cannot turn. It affects the labor number and we show that on the estimate rather than burying it in a square-foot rate.