Retaining walls are used to create a transition from one level of ground to another. By cutting into a slope and allowing for level ground both above and below the wall, retaining walls increase the amount of flat, usable ground in a yard. Building a retaining wall is suitable for DIYers as long as the wall is a maximum of 3 feet tall (in most areas). Anything taller should be handled by professionals.
The easiest way to build a stone retaining wall is to use the dry-stack method that requires no mortar between stones and does not need a concrete footing, like mortared walls do. Dry-stack walls also drain well, allowing water to pass through the wall itself. This helps reduce hydrostatic pressure imposed by wet soil behind the wall, which is the most common cause of retaining wall failure. Backfilling the wall with rock promotes drainage through the wall and prevents soil from pushing through the cracks in the wall’s stones.
Codes and Regulations
Check with your city’s building authority for applicable building code rules and zoning laws governing retaining walls. Most areas require an engineer’s stamp for walls over 3 feet, but some draw the line at 30 inches. Also, your city may require a permit and inspections for retaining walls of any height, even if you do the work yourself. Be sure to check before you build.
Call before you dig. Before breaking ground on your project, call 8-1-1, the national “Call Before You Dig” hotline, to have all underground utility lines marked on your property. This is a free service that can take a few days, so call well in advance of starting your project.
- Field stone or cut stone
- Landscape fabric
- Compactible gravel
- Coarse sand
- Drainage gravel
- Masonry adhesive (optional)
Organize the Stones
Organize the wall stones roughly by size and shape, making different piles as needed. You will use the largest, flattest stones for the base of the wall, and reserve the widest, smoothest, and best-looking stones for the capstones at the top of the wall. Keep in mind that odd sizes and shapes can be mixed in with more regular stones to maintain overall consistency, and you can knock off peaks and other formations with a brick chisel and maul, as needed, to make them fit during construction.
Set Up a Level Line
Use wood stakes and a mason’s line to mark the location of the front face of the base of the wall. The string also represents the front of the trench for the wall base. The width (front to back) of the trench should be at least one-half the total wall height. For example, if the wall is 30 inches tall, the trench should be at least 15 inches wide. Place a line level on the string, then pull the string taut from one end, and level the line before tying it off to the stake.
Excavate the Area
Excavate the area, starting from the string and moving back toward the slope. Dig down 12 inches into the ground to create a flat, level trench for the gravel base and first course of block, which will be below grade. Dig into the slope as needed to create a 6- to 12-inch-wide space between the backside of the wall and the slope, for drainage rock. Measure down from the level line to make sure the excavation is level as you go.
Add Landscape Fabric
Cover the excavated area with strips of landscape fabric (not plastic) laid perpendicular to the front of the wall and extending a few feet onto the upper-level ground. Overlap adjacent strips of fabric by 6 inches. Cut the strips to length with a utility knife.
Build the Wall Base
Fill the trench with 5 inches of compactible gravel. Rake the gravel so it is flat and level, then tamp it thoroughly with a hand tamp or a rented power tamper. Add a 1-inch layer of coarse sand over the gravel. Smooth the sand with a short 2×4 board so it is flat and level.
Lay the First Course
Set large, flat stones along the front edge of the trench to build the first course. Add or remove sand beneath each stone, as needed, so the tops of the stones are flush with one another. Use a 4-foot carpenter’s level set across multiple stones to make sure the stones are level as you work.
Lay the Second Course
Place the next course of stones on top of the first, offsetting (or “staggering”) the joints between stones with those in the first course, similar to the 1-over-2 pattern of bricklaying. This adds strength to the wall. Also, set the front faces of the stones about 1/2 inch back (toward the slope) from the front of the first course. This creates a slight stair-step pattern, called batter, that helps the wall resist forces imposed by the slope. As you place each stone, check that there is as little wobble as possible. You can use small, flat rocks as shims to prevent wobbling.
Begin Back-Filling the Wall
Fill the space between the wall and the slope with drainage gravel. Rake the gravel flat and level, and tamp it thoroughly with the hand tamp. Back-fill only up to the highest course on the wall.
Install More Courses
Lay the third and subsequent courses of stone, using the same techniques, adding 1/2 inch of batter for each course and staggering the joints with the course below. Starting with the third course, install “deadman” stones—long stones that reach back into the slope to help tie the wall into the earth. Place a deadman every 4 feet or so, and dig into the slope, as needed, so the stones sit level front to back. A wall that is 30 inches or less needs only one course with deadmen, but plan on two courses for a taller wall. Back-fill the wall with gravel as you go.
Complete the Top of the Wall
Fold the landscape fabric over the drainage gravel as you near the top of the wall. You can do this before the last one or two standard courses or before the capstones (the top-most course), depending on how much soil you’d like at the top of the wall (for growing grass). Lay the final course of stones and/or the capstones to complete the top of the wall. If desired, you can glue the capstones to the course below to help keep them in place, using masonry adhesive.
Back-Fill With Soil
Trim the landscape fabric so it is just below the top of the wall. Cover the landscape fabric and back-fill behind the top of the wall with soil, as desired. To grow grass in this area, the soil layer should be at least 6 inches thick.
Stone Retaining Wall Tips
You can build a stone wall with natural fieldstone that you have on your property, provided the stones are flat enough for stacking. If you have to buy stone, choose a flat stone, such as flagstone, or a cut stone like ashlar. Flat or cut stones are much easier to work with than fieldstone and will make a sturdier wall.
To create a more natural or aged look, plan to add plants in various places in the wall. Rougher stone will automatically have gaps large enough for packing in soil and planting. If you use cut stone, plan for plantable gaps when building the wall. They don’t need to be large and should not compromise the wall’s integrity. Cascading plants, such as creeping thyme, perennial yellow alyssum, and annual white alyssum, look very attractive spilling down the sides of stone retaining walls. Herbs also work well growing on or near rock walls.