How to Build a Retaining Wall

At Seattle Rockeries, we specialize in building high-quality retaining walls that serve to transform any residential property. However, we recognize that nobody knows your property better than you do. Sometimes you just want to roll up your sleeves and do it yourself! A retaining wall can be used to create more usable space in a yard and increase its visual appeal, so knowing how to build one is a great skill for any homeowner to have.

In this article, we are going to show you how to build your own concrete block or rock retaining wall from start to finish.

Before we get started, it is important to think about the design and placement of your retaining
wall. When it comes to DIY projects like this, proper planning is half the battle. Be sure to take extra time and care with this step!

Step 1 – Design and Planning

Materials

First, you need to decide what type of retaining wall you want to build and what specific materials you want to use. There are many different types of retaining walls, but this article focuses on concrete block and rock walls.

Block walls are perfect for getting a more tight, uniform look. Rockery walls, on the other hand, are great if you want to achieve a natural look, as every single rock will have its own unique shape and size.

* Excess rock wall material can also be repurposed for a rock garden

Your retaining wall will serve the same function regardless of which type you choose, so choose what you think will look best in your yard.

Once you’ve chosen the type of retaining wall, it is time to choose a specific material. What is available to you will greatly depend on your location and climate. In the Pacific Northwest, we have many materials readily available. These are some of the most common ones used for building retaining walls:

Block walls:

• Cornerstone
• Manorstone

* Ecology blocks are another common material used in the Pacific Northwest, but the extreme weight of each block makes this material more suited for industrial or commercial retaining walls.

Rock walls:

• Basalt 
• Granite rocks

Regardless of what you end up using, you need to ensure that your materials are designed specifically for retention and not just for aesthetic appeal. Be sure to ask yourself the following questions:

• If you are using concrete blocks, do the blocks have an interlocking design?
• Do your materials have any imperfections?
• Is your material heavy enough to withstand the weight of a dirt slope?

Drainage

In addition to your wall materials, you will need to think about what you will use for drainage. We recommend you use:

• crushed gravel
• drain rock
• filter fabric

These materials will be used to fill the space between the back of your retaining wall and the soil on your slope. Together, they work as a drainage system that filters water out of your soil. Without this, the water soaked up by the soil will add unnecessary weight and pressure to your structure. With the amount of rain we get in the Seattle area, proper drainage is critical!  

* You will want to leave 6 to 8 inches of space behind your wall for drainage

Tools

Once you have your materials, it is time to gather the necessary tools.

To build a retaining wall, you will need the following:

• Round point shovel
• Square blade shovel
• Rake
• Tamper
• Level
• Hammers
• Pick
• (optional) Excavator (+ a grappling bucket if you are building a rock wall)

You may already have some of these tools in your garage or tool shed. Otherwise, you should be able to buy or rent them from your favorite dealer.

Our preferred dealers/rentals:

• Herc Rentals
• Aurora Rents

Wall height and placement

Now it’s time to figure out the height and placement of your retaining wall.

*We recommend grabbing a pen and some graph paper to draw a diagram. Having a visual aid will help guide you throughout the building process. 

To determine the height and placement, find the midpoint of your slope – this is where you will place your wall. The highest point of your slope will determine the wall’s height.

* A wall up to 4 feet in height is ideal for a DIY project. Anything taller than 4 feet will require a permit from the city and the assistance of a licensed engineer. If your yard requires a retaining wall that is 4+ feet in height, contact us to get a quote!

The remaining dirt and soil on the wall’s front side will be excavated and used to backfill the gap between your wall and your slope. This will result in flattened portions on either side.

Step 2 – Excavation and Leveling

An excavator will be the quickest way to get this step done but a round point shovel is an ok (but time-consuming) alternative.

Here, you will be digging the trench for your retaining wall. You want to dig 6 to 8 inches down into your soil so that your base layer can sit below surface level. Part of your wall should be underground to help ensure that it doesn’t shift forward or backward.

Be sure that your trench is wide enough for your wall material, plus a few additional inches on either side so you have room to maneuver and work.

Next, dig up the soil that’s on the front side of your trench. We will use this to backfill the space behind your wall at the end of the process. You will also want to excavate an extra 6 to 8-inch area behind your trench, which is where your drainage will eventually go.

Step 3 – Prepare the Base

Before laying down your blocks or rocks, add a layer of crushed gavel to serve as your wall’s base. Shovel the gravel into your trench and use a rake to help achieve an even distribution. With a tamper, press down on the gravel to ensure the area is level. You should end up with a 2-inch layer of gravel for your wall to sit on top of. Having this gravel base further helps to keep your wall in place, which is important when you consider the amount of pressure it will be holding back.

Step 4 – Lay First Course of Blocks/Rocks

With a gravel base in place, you can now begin laying down your wall material.

Concrete block wall

This first layer is the most time-consuming since you need to make sure that every single block Is level. If this layer is not level, you risk the stability of your entire wall. Go along your trench, placing one block at a time. Make sure the blocks are as close to each other as possible. After each block, verify it is perfectly flat with your level tool. 

Rock wall

While laying block materials can be done by hand, you will need to use an excavator and its grapple bucket attachment to lay your rocks down along your trench. Since every rock is unique in shape and size, you won’t have a uniform or perfectly level row like you would with concrete blocks.

Step 5 – Add Additional Layers

Once your first course of material is laid down, it is time to lay down the additional rows.

Concrete block wall

Before adding additional layers, STOP. Is your first layer perfectly level? If so, go ahead and begin laying down your remaining rows.

It is the same process as before, but because you’ve already taken the proper steps to make sure the first layer is level, subsequent layers should go down much quicker. However, it doesn’t hurt to break out the level tool now and again to double-check your work.

It is also important to note that each layer will be offset from the previous layer so that the seams between each block are staggered. Referring to our diagram from earlier, each layer will also be placed slightly further back from the previous one, giving your wall a “staircase” look. This is done for the purpose of retention, as having the blocks staggered like this will help keep your wall from giving in to the pressure of the soil.

Rock Wall

Since every rock has its own unique shape and size, there will be some gaps between each rock in your wall. Before adding the second layer of large rocks, it is a good idea to use smaller rocks to fill those gaps. If you leave too many gaps in your wall, you are risking its stability.

Now repeat this process until you’ve reached the desired height for your retaining wall.

Step 6 – Backfilling and Leveling

Now that your wall is built, you should be left with a 6 to 8-inch gap between your wall and your slope.

Drainage

First, filter fabric needs to be placed between your wall and the soil behind the wall. The filter fabric has two sides. One side is porous and lets water come through, while the other side traps water so it doesn’t come through. Be extra careful to place your filter fabric with the porous side facing your soil. This will help keep water away from the wall. Next, you need to apply the drainage materials, which are placed in the gap between the wall and the filter fabric. Fill this gap with the crushed gravel and drain rock up to the top of your wall, leaving a few inches for your final layer of soil.

Backfilling and leveling

With the drainage in place, fill in the top of the remaining gap with soil and use your tamper to level everything out. This top layer of soil is for aesthetics.

After all this, you should end up with a beautiful new retaining wall! Even better, you can take pride in knowing that you did it with your own two hands.

Retaining Wall Ideas

If you need some design inspiration, check out these photos from projects we’ve completed in the past. All these walls went through the above steps (or some variation of them) to achieve the end result. Use these photos to help envision what you might want in your own yard!

Conclusion

Thanks for sticking around until the end!

Like any DIY project, the time and resources needed to build a retaining wall will vary. It will depend on the scope of your project and your level of experience. Whether you are an expert at hardscaping or a complete beginner, we hope this article helps guide you throughout the process.

With enough patience and dedication, a block or rock retaining wall can be the perfect addition to your property – elevating both its functional and aesthetic value.

If you have any questions about the building process or if you want the help of experienced professionals, do not hesitate to contact us! If you are curious about what other hardscaping services we provide, head to our website.