Natural Stone Retaining Wall: Building It to Last, and Costs

A natural stone retaining wall holds back soil using fieldstone, quarried stone or boulders, usually stacked dry (without mortar) so water can pass through. Built well, it lasts for generations; built badly, it bulges and collapses within a few winters. The difference is almost always below the surface: a compacted gravel base, a slight backward lean, and drainage behind the wall. HomeGuide puts natural stone retaining walls at about $10 to $85 per square foot of wall face, depending on the stone and wall type.

Types of natural stone walls

Type	Description	Typical cost per sq ft (national)
Dry-stack stone	Flat-bedded stones stacked without mortar	about $20 to $85
Boulder wall	Large boulders set with a machine	about $25 to $50
Mortared stone	Stone set in mortar on a concrete footing	higher; needs weep holes
Stone veneer	Stone facing over a concrete block core	about $30 to $80

Ranges are from HomeGuide; HomeAdvisor lists materials at about $25 to $80 per square foot plus $15 to $30 for labor.

The 4-foot line

Under the International Residential Code (R404.4), retaining walls that hold back more than 48 inches of unbalanced soil, or that support a slope or load above, need to be designed for that load. Many towns require a permit and an engineer's design above about 4 feet, measured from the bottom of the footing, and some set the line lower. Walls near property lines or driveways may have extra rules. Check before you build. For taller grade changes, consider two shorter terraced walls with a planting bench between them.

How to build a dry-stack stone wall

1. Dig the trench. About twice as wide as the wall's base stones and deep enough for 6 inches of base plus the first course partly buried.
2. Build the base. Compact 6 inches of crushed stone (like crusher run) in lifts. This is the wall's foundation.
3. Set the first course of your largest, flattest stones, partly below grade, tilted slightly back into the hill.
4. Batter the wall. Lean the face back about 1 to 2 inches for every foot of height. Gravity and the lean keep a dry wall stable.
5. Break the joints. Each stone should bridge the joint below it, one over two and two over one, like brickwork.
6. Add tie stones (long stones running back into the slope) every few feet in every few courses.
7. Backfill with drainage stone. Fill at least 12 inches behind the wall with clean gravel, not soil, and run a perforated drain pipe at the base, sloped to daylight.
8. Cap it with large flat stones, and finish with a few inches of soil and plants on top.

Why stone walls fail

• No compacted base, so the wall settles unevenly
• Soil backfill right behind the stones, which holds water and pushes the wall out when it freezes or gets saturated
• Vertical face with no batter
• Stacked joints (seams lining up) that split the wall into columns
• Too tall for a dry wall without engineering

Stone vs. other options

Natural stone looks best and lasts longest, but it's slow, heavy work. Segmental concrete blocks are faster and more predictable. For big, rough walls in a working yard or farm, interlocking concrete mafia blocks go up quickly with a machine. For accents rather than retaining, see landscape boulders.