Big natural stone, set by excavator on a compacted, drained base. The wall that looks like it has always been there, built so it stays that way.
A boulder retaining wall is built from large individual stones, usually 18 inches to 3 feet across, set in two or three courses with an excavator. Each stone is placed so it locks against the ones below and beside it, and each course steps slightly back into the slope. There is no mortar. Weight, fit and the setback do the holding.
It is the most natural-looking way to hold a slope, and in the Inland Northwest it fits the landscape better than anything else. The basalt and granite that come out of local yards are the same rock that already shows up on every hillside from the South Hill to Canfield Mountain.
Most boulder walls under 60 feet long take one to three days on site.
We charge $50 to $65 per square foot of wall face for boulder walls, with drainage included and a $4,500 project minimum. Face is height times length.
| Wall | Face | Typical price |
|---|---|---|
| 2 ft x 40 ft garden wall | 80 sq ft | $4,500 to $5,200 |
| 3 ft x 40 ft backyard slope | 120 sq ft | $6,000 to $7,800 |
| 4 ft x 60 ft driveway cut | 240 sq ft | $12,000 to $15,600 |
| Two 3 ft tiers, 50 ft each | 300 sq ft | $15,000 to $19,500 |
The things that push a wall to the top of the range are tight access, solid basalt in the base trench, and a lot of soil to haul off. All of it is checked on the site visit and written into the price. Full details are on the retaining wall cost page, and there is a deeper look at stone pricing on the boulder wall cost page.
Largest stones, fewest pieces, most natural look. Best for slopes, driveway cuts and anywhere scale helps. Needs room for an excavator.
Smaller stone, more pieces, tighter curves. Better for garden edges, along paths and where access is tight. Rock walls
Straight lines, crisp corners, built-in steps and caps. Fits newer subdivisions and HOA rules. Block walls
Not sure? Send us photos of the slope. We will tell you which one fits, and why, before we talk price.
A boulder wall over 4 feet tall, measured from the bottom of the footing, needs an engineered design and a building permit in Spokane County and in the Idaho cities we serve. Those walls also need much bigger stone and often geogrid reinforcement tied back into the slope.
We do not build them. Instead we terrace: two walls of 3 feet each, stepped back with a shelf between, will hold the same slope with less risk and give you usable ground in the middle. See tiered retaining walls for how that works.
Built on a compacted base with real drainage behind it, decades. Boulders do not rot like timber or crack like poured concrete. When a boulder wall fails early, the cause is almost always water trapped behind it or stones set on bare soil.
Usually 18 inches to 3 feet across, sized to the wall. The bottom course gets the largest stones.
Yes. Gaps between boulders let some water through, but not enough during the spring melt. We put drain rock, filter fabric and a perforated pipe behind every wall.
Not well. Boulders weigh from several hundred pounds to over a ton. If access is under about 5 feet wide, a stacked rock or block wall is usually the better choice.
Yes. We finish with topsoil over the drain rock so you can plant right to the edge. Avoid large trees within a few feet of the top.
Send a few photos and rough measurements. We reply with a price range, usually within one business day.