In order to terrace a hillside with stone retaining walls, it’s important to plan your terrace before you begin work. Once you’ve decided on the height of your terrace walls, build your first retaining wall at the bottom of the hill. To do this, dig an 8–10-inch deep trench, pour 4 inches of gravel in the trench, and lay your first course of stone. Build your wall to the desired height, backfill it with gravel and dirt, and level the terraced area. Once complete, you can move on up the slope and build additional terrace walls.
Table of Contents
10 Steps For Making a Terraced Slope with Stone Retaining Walls
A terraced hillside stops floodwater from racing downhill, where it can flood your lawn or house. It also combats soil erosion and helps the soil retain nutrients. Terracing can turn a barren hillside into a beautiful garden with herbs, flowers, or trees. Before you can begin constructing your terrace, you will need the following tools.
Tools and Materials:
- 2 or more 6-foot stakes
- Hammer or mallet
- Line level
- Measuring tape
- Carpenter’s level
- Landscape gravel
- Stone blocks
With these tools and building materials, you can terrace a hillside yourself. Here’s how:
Measure the Rise and Run of Your Slope
Before you start building terrace walls, it’s essential to plan the project. A terrace is essentially a series of steps cut into the hillside, so it’s important to plan the width and height of these steps before you start work. You need to plan the height and width of each wall to achieve symmetrical steps. For that, you’ll need to find the rise and run of the slope. Just follow these steps:
- Hammer the first stake into the ground at the top of the hill, where the rear of the last terrace step will end.
- Hammer the second stake into the ground at the foot of the hill, where the lowermost retaining wall will be.
- Tie your string to the base of the first stake (at top of the hill).
- Tie the other end of the string to the second stake (at bottom of the hill).
- Use your line level to ensure the line is level.
- Measure the distance between the ground and the point where the string is tied to the second stake. This is the amount of elevation increase (rise) between the base of the hill and the top.
- Measure the distance of the level string. This is the horizontal distance (run) of the slope.
- If your slope is too steep to tie a level line between the top and bottom stake, perform the above steps in sections. Add the rise and run of each section to find the total horizontal distance and elevation increase of the slope.
Once you have the total rise and run of your slope, planning a beautiful terrace is simple. While this may seem like a complex step, it’s essential to planning and executing a professional terrace.
Plan Your Terrace
Once you have the rise and run of your slope, you can plan your stone terrace. You will use these numbers to decide how many retaining walls you will build, what the wall height should be, and how wide to make each terrace step. Here’s an example:
- After measurement, the slope has a rise of 12 feet and a run of 32 feet.
- This slope can be terraced with four 3-foot retaining walls spaced 8 feet apart.
- This process leads to even terracing and a clean finished look.
- When planning, it helps to draw a quick sketch in order to envision the finished project and make adjustments as needed.
It’s important to keep in mind that the height of the retaining walls should be no more than half the width of the space between the walls. If you are building 3-foot walls, they must be spaced at least 6 feet apart. Any closer can lead to fallen walls.
Dig a Trench
Start your terrace at the bottom of the slope. Use your string and stakes to mark out a straight line. Then, dig a trench 8–10 inches deep. The trench should be 2–4 inches wider than the stones or concrete blocks you are using for your wall.
- Mark the path of your first retaining wall at the bottom of the hill.
- Dig an 8–10 inch deep trench along this line.
- Make the trench 2–4 inches wider than the stones or masonry blocks you intend to use as wall material.
- Angle the trench slightly backward (towards the hillside).
It’s beneficial to have a backward angle to your trench. The retaining wall should have a backward lean of 10–15 degrees. This helps prevent it from toppling forward. Don’t worry, the wall will be backfilled so there’s no chance of it falling back once it’s complete.
Once your trench is complete, pour a 4-inch layer of gravel into the floor of the trench. This allows water to drain below the retaining wall, which prevents erosion from undermining and destroying your terrace walls.
- Add 4 inches of gravel to the trench.
- Use landscape gravel, such as 3/4 inch gravel or crushed rock.
- Tamp the gravel for added stability.
Landscape gravel made from angular rock is the best choice for the job. Large gravel allows for proper drainage, while pea gravel or small rock compacts and makes for poor drainage material. If possible, it’s a good idea to tamp the gravel down firmly in the trench.
Lay the First Course of Stones
Now that your trench is ready, begin to lay your stones or masonry block in the trench. Position the stones at the front of the trench (downhill side). This will help it follow the backward slope of your trench. Then, backfill any gap behind the stones with additional landscape gravel for drainage.
- Lay initial stones in the trench.
- Position stones at the front of the trench (the side facing downhill), leaving a gap behind the stone and the rear of the trench.
- Fill the gap behind the stones with landscape gravel.
- Use a string and level to ensure the stones are level.
Take the time to verify that the first course of stones is level from one end of the trench to the other. This will make for a professional wall. To do this drive a stake at either end of the wall and stretch a string across the top of the first course of stones. Verify the string is level. Fix any low or high points in the wall by adding or removing gravel as necessary.
Build up Stone Wall
Now that you’ve got a level, well-drained wall started, continue laying additional courses of natural stone or masonry. Use an overlapping brick pattern to offset seams in the stones or blocks. Keep in mind, you can build a retaining wall without mortar as long as it is no taller than 3 feet. If your retaining wall is more than 3 feet tall, apply a layer of mortar between each course of stones.
- Lay additional courses of stones to reach desired retaining wall height.
- If the wall is 3 feet or less, no mortar is required.
- If the wall is over 3 feet high, you must use mortar between each course of stone.
- Maintain backward lean of the retaining wall.
- Check wall level periodically.
As you build the wall, keep in mind that it’s important to both have a slight backward lean to your retaining wall, as well as a level top. Use the string-and-level method to check the wall level if necessary.
Backfill Retaining Wall
Once your wall is complete, backfill it first with more gravel. If possible, a 2–4 inch wide gravel backfill should come up within 6 inches of the top of the wall. Then, continue to backfill the wall with dirt until it is fully supported.
- Backfill wall with 2–4 inch wide gravel fill.
- Gravel fill should stop 6 inches from the top of the wall.
- Backfill the rest of the space behind the wall with dirt from the hillside.
Once complete, your retaining wall will be properly supported and drained. Since it has gravel fill and leans slightly backward, it will resist erosion, shifting, and toppling.
Level the Terrace
With your wall in place, level the terrace “step” to the planned width behind the wall. In our example, the terrace has 3-foot walls with 8-foot wide steps. This will require some excavation, but the dirt can be used as backfill.
- Excavate the terrace step to the planned width.
- Grade the step. You can check the terrace level with a carpenter’s level for extra precision.
- Use excavated dirt as a backfill for existing walls, as well as the next retaining wall you build.
A level terrace step absorbs water, feeding the plants or grass planted there. This makes terracing ideal for planned gardens and orchards. A sloped hillside sheds water before plants can gather it, plus runoff strips the soil of nutrients as it washes through. Flat terrace steps create fertile ground for any plant you wish to grow.
Create Additional Retaining Walls
Once your first retaining wall is in place, simply repeat the process for as many terrace walls and steps as you have planned. It’s essential to work from the bottom of the slope to the top to give yourself a stable foundation as you go.
- Repeat previous steps for additional walls as necessary.
- Work from the bottom of the slope to the top.
Keep in mind, a moist ground is easier to excavate. It might be worthwhile to water the hillside the day before you work, to make the labor easier.
Plant the Terraced Hill
Once your terrace is complete, plant it with whatever garden varieties or ornamental grasses you desire. Fruit trees are common terrace plants because they grow large enough root systems to help keep soil in place but don’t grow so large that their roots invade retaining walls. Herbs, flowers, and vines are also great for terrace gardens.
- Turn each terrace step into a garden bed with mulch and soaker lines.
- Plant your terrace steps with fruit trees, ornamentals, herbs, vines, or grass to help prevent erosion.
- If you plan to create a terrace orchard or garden, don’t forget to include a stone stairway in your plans, to make climbing the hillside easy.
Rather than scramble up tall terrace walls, it’s a good idea to include a staircase in your planned terrace. This can make tending to a garden on a steep hillside much easier.
How Do You Terrace a Slope with Stone Walls?
To make a terrace that is held in place by stone retaining walls, it’s essential to follow these steps:
- Calculate the rise and run of your slope.
- Use the rise and run to plan wall height and terrace width.
- Dig an 8–10 inch deep trench for the first retaining wall at the bottom of the slope.
- Pour 4 inches of gravel into the trench.
- Lay the first course of stones or masonry blocks in the trench.
- Continue to build the wall, checking periodically to make sure it’s level.
- Backfill the retaining wall with gravel and soil.
- Level the terrace step behind the retaining wall.
- Repeat for the desired number of retaining walls.
- Plant the terrace garden with plants or grass of your choosing.
By following these steps, you can complete a professional-quality landscaping project yourself. These same principles can be applied to a steep slope or a gradual slope. In a short time, you can turn a hillside into a garden masterpiece.