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Homes and yards that are located on unlevel ground need to be leveled out. So do lots of other things around the yard—patios, pergolas, gazebos, raised gardens, sheds, walkways. Instead of grading down the entire slope, one method is to cut back the slope as far as needed, then hold up the rest of the earth with a retaining wall.
Retaining walls can last for decades if built properly. They can integrate with your property and open up areas that you may have once thought unusable.
What Is a Retaining Wall?
Different walls address different needs. Some tall, lightweight walls protect your privacy; other walls may define spaces. If you just want a wall to reduce sound, mark property lines, or to keep in livestock, pets, or children, nothing is more simple than erecting a wall of cinderblocks, vinyl, or wood.
A retaining wall operates quite differently from other exterior walls. A retaining wall primarily does one thing: it retains the soil packed behind it. The empty space behind the retaining wall is backfilled not with soil but with a porous, drainage-promoting material such as gravel or sand.
How a Retaining Wall Works
Heavy retaining wall blocks—each weighing 14 pounds, with this project—keep the soil at bay with their weight. Some do-it-yourself retaining wall blocks weigh as much as 61 pounds.
But it's the blocks' accumulated weight that does the trick. A three-tier wall with a 14-pound block weighs close to 500 pounds for each 8-foot stretch.
As the wall goes higher, it tilts backward. This has the same effect as a wrestler leaning forward to try to pin an opponent. Weight plus tilt result in retention.
A lip on the backside of the block helps you to position a block on top of the block below it.
Permits and Codes
In many communities, certain characteristics must be present for walls and fences to require permitting or fall under zoning restrictions. Retaining walls may or may not require permitting in your community. Consult your local permitting department for advice.
In some communities, the need for a permit is not triggered if the retaining wall remains lower than 4 feet and is not located in an environmentally critical area. The retaining wall must also be constructed with sound building practices and cannot damage any areas around it, whether direct or indirect.
When to Build a Retaining Wall
Build the retaining wall when the soil is at its driest. Wet earth is both hard to shovel into and hard to move. Wait until well after the latest round of precipitation for the soil to fully drain out, before starting the retaining wall.
- Working Time: 4 hours per 8 linear feet
- Total Time: 5 hours
- Skill Level: Intermediate
- Material Cost: $60 to $100
What You'll Need
- Bubble or laser level
- Masonry or cold chisel
- Sledgehammer or framing hammer
- Safety glasses
- Tape measure
- Two-by-four lumber, one short piece of scrap
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- 35 retaining wall blocks, each 4-inch by 8 1/2-inch
- Drain rock or sand
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Level the Ground
With a flat blade shovel, grade the soil where the blocks will rest until the soil is flat, level, and compact. Use the short two-by-four as a screed to further level the soil by drawing it towards you, scraping off soil to create a level area.Continue to 3 of 12 below.
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Lay Sand or Gravel as Base
One idea behind a sand or gravel base is that it will keep your lowest course of blocks above any mud. Water will inevitably seep to the bottom of your wall, and when it collects at the base, it will turn into mud. By laying one or two inches of base, you raise the lowest row above this mud.Continue to 4 of 12 below.
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Lay the First Line of Blocks
Begin one end of the wall with a single block. Press it firmly down into the base, though not so hard that you squeeze the base layer away. Use your level to check this first block for the level in both directions: from side to side and from front to back.Continue to 5 of 12 below.
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Maintain Level of Each Block
Lay down the next adjoining block. This block must be perfectly level both on its own and in conjunction with the adjoining block. Use the bubble or laser level to span from one block to the next. Adjust the second block until it is perfectly in line with the first block.
Aligning from block-to-block is highly important. As you continue to add courses of blocks upward, any differences between lower blocks will be transmitted to upper courses, often in disastrous ways.Continue to 6 of 12 below.
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Lay the Blocks Staggered
Lay blocks in a brickwork fashion, advancing each upper row horizontally one-half block over. Brickwork masonry is enormously more stable than independent vertical columns.Continue to 7 of 12 below.
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Check Level With Each Course
Every row must be level. Keep spot-checking your level with the bubble or laser level. The only way to keep an entire row at a true level is to run a string between two posts pounded into the ground at either end of the wall. For posts, use spare plumbing pipe, one-by-ones with the ends cut into points, or rebar.Continue to 8 of 12 below.
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Set Chisel in Groove to Cut Block
To cut a retaining wall block in half, set the block on end, with the back side facing up. You will notice a V-notch groove in the back of the block.Continue to 9 of 12 below.
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Cut the Retaining Wall Block
With the sledgehammer and holding near the head, or with a framing hammer, sharply strike the end of the chisel until the block cleaves in half. You may need to strike several times for the block to break.Continue to 10 of 12 below.
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Set Half-Block at End of Row
Use one of the cut half-blocks to cover the end of the row.Continue to 11 of 12 below.
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Check Room on the Backside
When laying out the retaining wall, provide ample room between the lowest course of blocks and the soil behind it. As the blocks progress upward, they will tilt backward. So you will need to cut back more of the hill than you might initially think.Continue to 12 of 12 below.
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Backfill With Sand or Gravel
Carefully fill the backside of the retaining wall with sand or gravel. This process is called backfilling.
Portion out the backfill material in small amounts in order to let the material settle. If you shovel too much at once, you may create hollow spaces in the backfill that can compromise the wall's stability.
Occasionally jiggle the wall front-to-back in order to coax the backfill material into settling. The more compact the backfill, the more stable your wall will be over the long term.