Boulder Retaining Wall Cost & How to Estimate One
Part of Landscaping & Aggregate
Quick answer
A boulder (rock) retaining wall typically costs $25–$60 per face square foot installed, driven mostly by boulder size, delivery and machine time. To estimate one: find the wall's face area (length × height), order boulders by the ton for that volume, and add a compacted gravel base and drainage stone behind it. A 30 ft × 3 ft wall (90 face ft²) runs roughly $2,500–$5,400 installed.
Boulder walls hold back soil with large stacked rocks instead of block or poured concrete. Cost and materials scale with the wall's face area (length × height) and the size of boulder you use — bigger boulders mean fewer pieces but more machine time.
How to estimate the materials
- Face area = wall length × exposed height (in feet).
- Boulders: estimate the rock volume (face area × average boulder depth) and order by the ton — landscape boulders run ~1.3–1.5 tons per cubic yard.
- Base: a 6–12 in compacted gravel/crushed-stone footing the full length, set below grade.
- Drainage: washed drainage stone and often a perforated pipe behind the wall so water doesn't build up and push it over.
Typical installed cost
| Wall | Face area | Installed cost |
|---|---|---|
| 20 ft × 2 ft | 40 ft² | $1,000–$2,400 |
| 30 ft × 3 ft | 90 ft² | $2,500–$5,400 |
| 50 ft × 4 ft | 200 ft² | $5,000–$12,000 |
What drives the price
- Boulder size and type — larger and decorative stone costs more and needs bigger equipment.
- Delivery distance — stone is heavy, so hauling is a real cost.
- Site access and excavation for the base and any tie-back stepping.
- Wall height — taller walls may need engineering or terracing.
Use the gravel and stone calculators to size the compacted base and drainage stone behind the wall, then price the boulders by the ton from a local landscape-supply yard.
FAQs
How much does a boulder retaining wall cost per foot?
Plan on roughly $25–$60 per face square foot installed, or about $50–$200 per linear foot depending on the wall's height. Material-only (DIY) costs are lower but you'll need a machine to set large boulders.
Do boulder walls need a gravel base?
Yes. Set the first course on a compacted crushed-stone base below grade so the wall doesn't settle or heave, and pack drainage stone behind it so water can escape rather than push against the boulders.
How tall can a boulder wall be without engineering?
Many jurisdictions require an engineer's design above about 3–4 feet. Taller slopes are often handled with terraced (stepped) walls instead of one tall wall. Check your local code before building.