Step-by-step guide for a gravity retaining wall using concrete blocks — the most DIY-friendly type for residential use. Covers walls under 4 feet (no engineering required in most jurisdictions).
Important: Walls over 4 feet tall, walls near structures or property lines, and walls on slopes above occupied areas require engineering and permits in most jurisdictions. Check local codes before building.
| Material | Quantity |
|---|---|
| Retaining wall blocks (6×12×8" typical) | Varies by wall size |
| Cap blocks | 1 per linear foot |
| 3/4" crushed gravel (base + drainage) | ~0.5 cubic yard per 10 lf |
| 4" perforated drain pipe | 1 per linear foot + 10% |
| Landscape fabric | ~2x wall height × wall length |
| Construction adhesive (cap) | 1 tube per 20 lf |
| Block adhesive pins (optional) | Per manufacturer |
Use our Retaining Wall Calculator to get exact block and material quantities for your wall dimensions.
Check local codes for height limits and permit requirements. For walls under 4 feet, most areas don't require a permit, but verify. Call 811 to locate buried utilities before digging — free service, required by law. Mark the wall line with spray paint or stakes and string. Determine where the drain pipe will daylight (exit) at each end.
Dig a trench along the wall line. The first course of block needs to be buried at least halfway — for a 6-inch tall block, bury 3 inches minimum. Typical trench is 12 inches deep and 18–24 inches wide to accommodate the block plus 12 inches of gravel drainage space behind. Keep the trench bottom level — use a long level or laser level to check.
Fill the trench bottom with 6 inches of compacted crushed gravel (3/4-inch clean crushed stone, not pea gravel). Compact in 3-inch lifts with a plate compactor or hand tamper. A properly compacted base is the single most important factor in wall longevity. Soft base = wall that settles and tilts within a few years.
Place the first course of blocks on the gravel base. Check every block for level in both directions — front-to-back and side-to-side. Set the level check before moving to the next block. If you rush this step and the first course is off, every subsequent course amplifies the error. Tap blocks with a rubber mallet to adjust. Backfill gravel behind the first course and compact it before continuing.
Most retaining wall blocks have a built-in setback (batter) of about 1 inch per course, tilting the wall into the slope. Set each course back from the previous one per the manufacturer's instructions. Offset vertical joints between courses (running bond pattern) for strength — don't stack joints directly above each other. Backfill and compact 6 inches of gravel behind each course as you go.
Behind the base course, lay a 4-inch perforated drain pipe wrapped in landscape fabric sock (or wrap it yourself). The pipe should slope toward the daylight end at minimum 1% grade. Cover the pipe with additional clean gravel, maintaining 12 inches of gravel drainage zone behind the wall. The pipe channels water that would otherwise build pressure against the wall.
Once all courses are stacked, backfill the upper section with native soil (not clay) in 6-inch lifts, compacting each lift. Maintain the 12-inch gravel zone immediately behind the wall. Cover the top of the gravel with landscape fabric before adding soil to prevent soil migration into the drainage zone. Apply construction adhesive to the cap blocks and set them across the top, offsetting the joints.
The number one cause of retaining wall failure. Water pressure from saturated soil is enormous. Always install a perforated drain pipe and clean gravel drainage zone, no exceptions.
A block wall on an uncompacted base will settle, tilt, and eventually fail. Compact the base gravel in lifts with a plate compactor — hand tamping is not enough for a tall wall.
If the first course isn't level, the wall isn't level. A 1/8-inch error in the first course becomes a 1-inch error by the eighth course. Spend the time to get course one perfect.
Like brickwork, retaining wall blocks must be laid in a running bond — vertical joints offset between courses. Stacking joints creates a structural weak point.
Taller walls require structural engineering to properly account for soil load, drainage, and footing design. A wall failure above 4 feet can injure people and damage property.
Most building codes allow gravity retaining walls up to 4 feet without a permit or engineering design. Some jurisdictions limit it to 3 feet. Anything near a structure, driveway, property line, or holding back a slope above a walkable area typically requires engineering regardless of height.
Yes, always. Without drainage, water saturates the soil behind the wall, increasing its weight and building hydrostatic pressure against the wall face. Even a well-built wall will fail under sustained water pressure. A perforated drain pipe and clean gravel backfill are not optional — they're what keeps the wall standing.
Retaining wall blocks (also called Allan Block, Versa-Lok, or similar) are designed with a built-in setback and connection system. Don't use standard concrete blocks or decorative garden blocks for load-bearing retaining walls — they don't have the structural geometry required.
A 20-foot long, 3-foot tall wall typically takes a weekend for one or two people with no complications. Excavation and base prep takes the most time. Once the base is level, stacking the blocks goes quickly. Don't rush the first course — getting it perfectly level makes every subsequent course fast.
Yes, for walls under 4 feet using standard retaining wall blocks. The work is physically demanding (blocks weigh 40–80 lbs each) but not technically complex. The critical skills are: digging a flat trench, compacting base gravel, and getting the first course perfectly level.
DIY materials for a basic concrete block retaining wall run $10–$20 per square foot of wall face. Professional installation runs $25–$50 per square foot depending on wall height, access, and soil conditions. A 20-foot by 3-foot wall (60 sq ft face) costs $600–$1,200 DIY in materials.