Walls that rock

Should you build a rock wall yourself? You can build low walls, but anything taller than 2 to 3 feet is best tackled by a professional. If the wall is meant to hold back a slope, consult an engineer.

•Foundation: Use 6 to 12 inches of crushed rock for short walls (1 to 3 feet high); concrete should be used for tall or heavy walls. Embed the footing, as well as the first layer of rock, in the soil.

•Height: In most cases, the slope will determine the wall's height. For steep slopes, build several walls to form terraces (as shown on page 56, lower left). If you plan to use the wall for seating, build it about 18 inches high.

•Placement: For stability, place widest rocks at the bottom of the wall. Overlap, or stagger, rock edges as you build, and angle the wall back toward the slope 10° (about 1/8 to ¼ inch back from the preceding row, depending on site). Choose pieces that fit like a puzzle and set each one firmly in place. Use small stones to level large ones and to fill in gaps.

•Drainage: Pack soil firmly behind each layer of rock. If the slope seeps water, place a 3- to 4-inch-thick layer of crushed rock directly behind the wall.

•Price: Stone costs vary widely. Fieldstone costs about $125 per ton; sandstone or strip flagstone about $260 per ton; imported granite and basalt up to $500 per ton.