A retaining wall holds back soil on a slope, creating flat usable areas in your yard. Small retaining walls — under 3 feet tall — are solid DIY projects using interlocking concrete blocks or natural stone. Taller walls involve serious engineering and should be designed by a professional.

How to Build a Small Retaining Wall

When You Can DIY

Most municipalities allow homeowners to build retaining walls up to 3 feet tall without a permit or engineering plan. Walls over 3 feet typically require a permit, a structural engineer’s design, and often a licensed contractor.

Check your local codes before starting. Even a short wall can cause drainage problems or property disputes if built improperly.

Material Choices

Interlocking concrete blocks are the easiest option for DIY builders. They are uniform in size, have built-in lips or pins that lock each course to the one below, and require no mortar. Brands like Allan Block, Pavestone, and Belgard are available at most home improvement stores.

Natural stone looks more organic but requires more skill to lay. Stones vary in size and shape, so you spend more time fitting and shimming. Fieldstone and flagstone are popular choices.

Treated timber walls (landscape timbers or 6x6 posts) are the cheapest but have the shortest lifespan — 10 to 15 years before rot sets in.

Tools

Shovels and wheelbarrow
Tape measure and stakes
String line and level
Plate compactor (rent one)
Hand tamper
Rubber mallet
Angle grinder or masonry saw for cutting blocks
Safety glasses and gloves

Excavation and Base

Dig a trench along the base of the wall. The trench should be 24 inches wide and deep enough to bury the first course of block at least halfway below grade. For a wall using 8-inch-tall blocks, dig down about 6 inches below the finished grade.

The buried course is essential. It anchors the wall against sliding and prevents the base from being undermined by erosion.

Compact the bottom of the trench with a hand tamper. Add 4 to 6 inches of crushed gravel (3/4-inch minus), spread it evenly, and compact it with the plate compactor. Check for level along the length — this is your foundation, and errors here show up in every course above.

Laying the First Course

The first course is the most important. Set each block on the compacted gravel, tap it level with a rubber mallet, and check level side to side and front to back. Also check level between adjacent blocks.

Spend as much time as you need on this course. A perfectly level first course makes every subsequent course fast and easy. A sloppy first course makes the wall look bad and eventually fail.

Building Up

Stack subsequent courses with joints offset — like a brick pattern. The interlocking lip on the back of each block automatically sets the correct setback (the slight lean toward the soil). This lean, called batter, resists the horizontal pressure of the soil behind the wall.

Check level frequently. Adjust by tapping blocks with the rubber mallet or shimming with thin pieces of stone.

Drainage

Water pressure behind a retaining wall is the number one cause of failure. You must provide drainage.

Gravel backfill: Fill the space behind the wall with 3/4-inch crushed gravel to within 6 inches of the top. Cap with native soil and sod. The gravel allows water to drain down rather than building up pressure against the wall face.

Drain pipe: For walls over 2 feet tall, lay a perforated drain pipe (4-inch PVC with sock) at the base of the wall, bedded in gravel. Route the pipe to daylight at the end of the wall or connect it to a drainage system.

Filter fabric: Line the back of the gravel backfill zone with landscape fabric to prevent fine soil from migrating into the gravel and clogging the drainage.

Capping

Install cap blocks on the top course. These are flat, wider blocks that overhang the wall face slightly and give the wall a finished look. Glue them down with landscape block adhesive — they do not have interlocking lips.

Common Mistakes

Skipping the gravel base. Setting blocks directly on dirt invites settling and heaving. The gravel base is not optional.

No drainage behind the wall. Saturated soil is dramatically heavier than dry soil. Water pressure will push the wall over.

Building too tall without engineering. Soil pressure increases exponentially with height. A wall that works at 2 feet may fail catastrophically at 4 feet. Stay under 3 feet for DIY, or hire a licensed professional for taller walls.

Not burying the first course. An exposed base course will eventually slide forward under soil pressure.

A well-built retaining wall transforms a useless slope into functional garden space or a level patio area. Take your time with the base and drainage, and the wall will outlast most things in your yard.