How to Build a Retaining Wall

How to Build a Retaining Wall

Planning a Block Retaining Wall

How to Build a Retaining Wall

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There are several retaining wall systems to consider when choosing the building materials for your wall. You can choose regular block that simply stack together for a gravity-held wall, a block system that works with pins for easy and secure assembly or block with an interlocking lip as we did for this project. The lip creates a locking flange on the block, making your retaining wall ideas easier to accomplish. The interlocking retaining wall block can be stacked to build walls up to 24 to 36 inches high, depending on the size of the block. Follow the block manufacturer’s instructions for wall height limits.

Plan your layout. Avoid having downspouts pointed at the retaining wall and, if it’s against the house, keep soil and mulch well below the siding.

Your retaining wall design will determine how you mark the area. To mark a free-form layout, use a rope or hose to outline the shape. Then use a shovel to mark the outline. For straight lines, mark the entire bed area with stakes, string and marking paint. Mark curved corners by tying a string to a stake that’s equidistant to the edge — creating a compass — and spraying the curves with marking paint.

To determine how many block you’ll need per row, divide the total length of the wall by the length of the block. To see how many rows you’ll need, divide the ideal wall height by the height of the block; account for the first row to be half-buried. See our Retaining Wall Block Calculator and Planning for a Block Retaining Wall for more information on estimating project materials.

Before you buy materials or begin work, check local building codes and your homeowners association regulations to see if there are any restrictions or requirements you need to follow. A permit may be mandatory in some areas.


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Tip

Purchase 10% more block than your estimate. The excess should account for breakage, cutting and replacements for future repairs. Block can be heavy so wear a back support if necessary. You may want to enlist a helper to share the work. Consider having the material delivered.

Prep and Lay the Retaining Wall Block

Now that you have a plan and a layout, prep the area and begin building the retaining wall.

Prepare the Foundation

How to Build a Retaining Wall

With the layout marked, you can begin digging the trench. To bury the first course or first row about halfway, dig the trench about 4 to 6 inches deep and 12 inches wide or twice the width of the block.


Caution

Before beginning any excavation, call 811 to check for underground utilities.

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How to Build a Retaining Wall

If the trench slopes, you’ll have to step up or down to keep the blocks level. Use a torpedo level to create steps so that each section of the wall remains level. You do not want the wall to run parallel to the slope.

How to Build a Retaining Wall

Tamp down the dirt with a hand tamper and keep it level.

How to Build a Retaining Wall

Fill the trench with about 3 inches of paver base, spread it with a rake and tamp it down. Tamping the base provides a strong foundation. When it’s all level, you can begin installing the block.


Tip

Wet the paver base if it’s dry and dusty.

Build the Retaining Wall

How to Build a Retaining Wall

Beginning at the end of the trench at the lowest elevation, set the first block in place and check for level.

How to Build a Retaining Wall

Place the next block, making sure it’s even with the first. Continue installing the first row, periodically checking for level.


Tip

A 6- to 9-inch torpedo level is useful for checking level of individual block or checking level front to back. A longer carpenters or masons level — 24 inches and up — is good for checking level over several block.

How to Build a Retaining Wall

To level the rows and keep them even, fill in under a low block with paver base or tap down high block with a rubber mallet.

How to Build a Retaining Wall

After installing each row, sweep dirt off the tops.

How to Build a Retaining Wall

To start the second row, you’ll have to cut a block to stagger the joints. Mark it and cut it with a masonry blade.

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How to Build a Retaining Wall

Put the cut block in place, keeping the flange tight against the first row. Check it for level.

How to Build a Retaining Wall

After installing the next few rows, you’ll need to add drainage directly behind the block. Lay down landscape fabric behind the wall, leaving enough excess to reach the top of the block.

How to Build a Retaining Wall

Fill in directly behind the wall with gravel as you build.

How to Build a Retaining Wall

For the last two rows of full block, apply concrete adhesive to the wall block tops and then set the next row of block in place.


Tip

If you’re adding block caps, apply adhesive to the top row of block before placing the caps.

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How to Build a Retaining Wall

Fold the excess fabric back. Backfill with raised bed soil and add plants.

Retaining Wall Ideas

How to Build a Retaining Wall

Once you know how to build a block retaining wall, think about some different DIY landscape ideas for retaining walls.

Mix and match different block colors to create a custom wall. Or capture the perfect look by choosing your style of block. In addition to block with beveled or straight faces, you can find block with the look of tumbled natural stone or rounded fieldstone, chiseled-face block with the appearance of worked stone or block that creates the look of a stacked-stone retaining wall.

And, while retaining walls are perfect for creating raised planting beds, there are other hardscaping design ideas for incorporating a retaining wall into your landscape.

  • Break up a lawn with raised beds, adding new textures, colors and planting opportunities, while reducing lawn maintenance.
  • Go beyond a basic flower bed with stair-stepped walls for multilevel plantings.
  • Define a patio space while adding planting opportunities. Better yet, plan your retaining wall design to create nooks for a dining space, cooking area, fire pit or other conversation areas.
  • Add terraces to a sloped yard or a hillside to make the landscape more usable and help control erosion.
  • Define a driveway, sidewalk or walkway with a course of retaining wall block, or beautify them by lining them with raised flower beds.
  • Incorporate a raised bed into a backyard pond or water feature.

Beyond standard retaining wall ideas, consider other uses for retaining wall block. Some wall block can work for a fire pit, benches, mailbox surrounds or decorative columns and walls.

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