Boulder Retaining Wall

What This Service Involves

Boulder retaining walls use large quarried rocks placed by machine to hold back steep grades common on Western Washington hillside lots. The generous gaps between boulders allow groundwater to seep through freely, which is a major advantage in our rain-heavy region, though we still add gravel backfill and drainage behind the wall on taller installations. Each boulder is nested and keyed into the one below so the wall resists sliding even in saturated soil. The finished wall reads as a natural rock outcropping and needs almost no maintenance.

Benefits

Excellent free-draining performance in wet climates; Handles steep slopes and heavy loads; Bold, natural rock-outcrop appearance; Minimal long-term maintenance; Very long lifespan with no mortar to fail

Our Process

1) Excavate and bench the slope; 2) Compact a stable gravel base trench; 3) Set and key the largest base boulders; 4) Stack upper boulders while adding gravel backfill and drainage; 5) Blend the top boulders into finished grade and plantings

What Affects the Cost

Boulder size and quantity; Machine access to the site; Slope height and steepness; Trucking of heavy stone; Base preparation and drainage backfill

Best Time of Year

Best placed in drier spring-through-fall conditions when heavy equipment can work the slope without churning saturated PNW soil.