How to Build a Cinder Block Retaining Wall: Step-by-Step Guide

June 1, 2026

Before You Start: When You Need a Permit

Most jurisdictions require a building permit for retaining walls over 4 feet high (measured from the bottom of the footing). Walls under 3 feet are typically exempt. Check with your local building department before breaking ground — code violations can require demolition.

For walls over 4 feet, a structural engineer should design the footing and rebar schedule. This guide covers residential-scale walls up to 4 feet total height.

Step 1: Calculate Your Materials

Before ordering materials, calculate the total block count using the Cinder Block Calculator. For a retaining wall:

Wall length: Measure the horizontal run of the wall
Wall height: Measure from finish grade on the low side to finish grade on the high side
Block type: Standard 8×8×16 for walls under 4 feet; 12×8×16 for added mass on taller walls

Standard 8×8×16 blocks require 1.125 blocks per square foot of wall face. For a 20-foot long, 3-foot high wall:

Wall area: 20 × 3 = 60 sq ft
Blocks needed: 60 × 1.125 = 67.5 → 68 blocks + 10% waste = 75 blocks

Order mortar separately: approximately 8.5 bags of 80 lb mortar per 100 blocks.

Step 2: Plan Your Footing

A retaining wall requires a concrete footing below the frost line. The footing distributes the weight of the wall and the retained soil load.

Footing dimensions for a standard residential retaining wall:

Wall Height	Footing Width	Footing Depth	Footing Thickness
Up to 2 ft	16 in	Below frost line	8 in
2–3 ft	24 in	Below frost line	8 in
3–4 ft	32 in	Below frost line	12 in

The frost line depth varies by location — from 0 inches in southern states to 48+ inches in northern Minnesota. Check your local frost depth requirement.

Footing is typically not required for:

Walls under 18 inches high on undisturbed soil
Dry-stacked block walls (no mortar) under 2 feet

Step 3: Excavate and Set the Footing

Mark the wall line with stakes and string
Excavate to the footing depth plus the footing thickness
Tamp the base of the excavation firmly — any soft spots will cause settlement
Set forms from scrap lumber or purchase foam footing forms
Pour concrete and screed level — the footing must be level across its length
If using rebar: set vertical rebar (typically #4 or #5) in the footing before the concrete sets, spaced every 24–32 inches on center for reinforced walls

Allow the footing to cure for at least 48 hours before laying blocks. Cure time extends to 72 hours in cold weather.

Step 4: Lay the First Course

The first course is the most critical — it establishes level and alignment for every course above it.

Dry-lay (no mortar) the first course along the footing to check spacing and length
Mix mortar to a peanut butter consistency — it should hold a peak but not be runny
Spread a 3/4-inch bed joint of mortar on the footing
Set the first block at one end, checking for level in both directions
Lay blocks toward the other end, checking level every 2–3 blocks
Use a story pole or level to verify each block is at the same height

Grout cores (for reinforced walls): If rebar was placed in the footing, align the block cores over the rebar. Fill cores with grout (not standard mortar) after every 2 courses.

Step 5: Subsequent Courses and Batter

Running bond pattern: Offset each course by half a block (8 inches) from the course below. This is standard for structural walls — never stack blocks in a straight vertical joint.

Batter (wall lean into the slope): A retaining wall should lean slightly into the retained soil — typically 1 inch of setback per foot of height. This is called batter and counteracts the horizontal pressure of the soil.

Wall Height	Recommended Setback
1 ft	1 in
2 ft	2 in
3 ft	3 in
4 ft	4 in

Achieve batter by setting each course slightly toward the slope — use a batter gauge or measure from a plumb reference point.

Step 6: Plan Drainage

Drainage failure is the most common cause of retaining wall collapse. Water pressure (hydrostatic pressure) behind a wall dramatically increases the load on the blocks and footing.

Required drainage for any retaining wall:

Gravel backfill: Use 3/4-inch crushed stone (not pea gravel) directly behind the wall, extending 12 inches from the block face for the full height of the wall
Drain pipe: Install perforated 4-inch PVC drain pipe at the base of the wall, wrapped in filter fabric, sloped to daylight (minimum 1% slope)
Weep holes: Leave every 4th head joint open (no mortar) at the base course. These allow water that gets through the gravel to escape through the wall face

Never backfill with native soil directly against the block wall — clay soils retain water and can exert 2–3 times the pressure of granular fill.

Step 7: Backfill

Backfill in lifts of 6–8 inches, compacting each lift with a hand tamper. Never compact within 18 inches of the back of the wall — use hand compaction near the wall, mechanical compaction farther away. Excessive compaction pressure against the wall before mortar has fully cured can crack the blocks or push them out of alignment.

Allow mortar to cure for 7 days before placing heavy loads on the retained side.

Common Retaining Wall Mistakes

Mistake	Consequence	Fix
No drain pipe	Hydrostatic pressure, wall failure	Install perforated pipe at base
Clay soil backfill	Water retention, excess pressure	Use crushed stone for 12 in behind wall
Footing above frost line	Settlement and cracking	Dig to frost depth
No batter	Wall leans out over time	Set each course 1/4–1/2 in toward slope
Vertical joints aligned	Structural weakness	Offset each course by half a block

For total block count and mortar quantities for your retaining wall project, use the Cinder Block Calculator. For cost estimates including materials and labor, see Cinder Block Cost Per Block and Pallet.