Difficulty
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DIY Cost
A retaining wall solves erosion, creates usable terraced space, and adds serious curb appeal — but contractors charge $6,000–10,000 for a basic wall. With the right blocks, proper drainage, and patience on the base, you can build one yourself for $800–2,500. I've built dozens of these. Here's exactly how. Once the wall is done, many homeowners finish the terraced area with a stone patio to create a complete outdoor living space.
Materials List (for a 24" tall × 20' long wall)
Retaining Wall Blocks
~120 blocks (6"×12"×8" each) — estimate 1 block per linear foot per course
Cost: $300–600
Crushed Stone Base
2–3 tons of 3/4" crushed stone for footing trench and drainage
Cost: $80–140
Drainage Pipe
20+ feet of 4" perforated drain pipe (runs behind wall)
Cost: $40–60
Landscape Fabric
Heavy-duty fabric to wrap drainage stone and block fine soil migration
Cost: $30–50
Construction Adhesive
Landscape block adhesive for cap blocks and wall corners
Cost: $20–35
Compactable Gravel
3/4" clean gravel for backfill directly behind wall (NOT soil — soil traps water)
Cost: $60–100
| Item | Estimated Cost |
|---|---|
| Retaining wall blocks | $300–600 |
| Crushed stone (base + drainage) | $140–240 |
| Drainage pipe | $40–60 |
| Landscape fabric | $30–50 |
| Construction adhesive | $20–35 |
| Compactable gravel (backfill) | $60–100 |
| Tool rental (compactor, level) | $60–80 |
| Total DIY Cost | $650–1,165 |
| Professional installation | $4,000–8,000 |
| Your Savings | $3,000–7,000 |
Step-by-Step Construction
Plan and Mark the Layout
Use stakes and mason's line to mark the front face of the wall. Keep it straight or gently curved — tight curves require cutting blocks. Mark where drainage outlets will exit the wall face (every 6–8 feet).
Calculate your block count: Linear feet × courses needed. For a 24" wall with 8" blocks, you need 3 courses minimum (with the base course buried).
Excavate the Base Trench
Dig a trench 6–8 inches deep and 24 inches wide along the wall line. For every foot of wall height, bury one course of block below grade — this is your buried footing that holds everything.
For a 24" finished wall: dig down 8–10 inches, place the first course 6–8" below final grade. Compact the trench bottom thoroughly.
Install the Base Course — The Most Critical Step
Add 6 inches of compacted crushed stone to the trench. Level it perfectly — every imperfection multiplies with each course. Use a 4-foot level constantly.
Place base course blocks with the front lip facing out. Offset block joints (like bricklaying) — never stack joints on top of each other. Check level after every 3–4 blocks.
Install Drainage Before You Stack
After the base course is set, run perforated drain pipe behind it (perforations facing down). Wrap the pipe in landscape fabric to prevent clogging. The pipe must outlet through the wall face or to daylight at each end.
Cover the pipe with 6–12 inches of clean gravel. This is what keeps hydrostatic pressure from building up behind the wall — skipping drainage is why walls fail.
Stack Remaining Courses with Batter
Each course should set back 1 inch behind the one below it — this is called "batter" and it's what gives retaining walls their strength. Most interlocking blocks have a built-in lip that automatically creates batter.
After adding each course, backfill behind it with compactable gravel (NOT soil). Compact every 4–6 inches. Never use soil directly behind the wall — it retains water and pushes the wall forward.
Install Cap Blocks
Cap blocks finish the top of the wall with a clean, flat surface. Apply construction adhesive under each cap block. Press firmly and check that they're level. Allow adhesive to cure 24 hours before disturbing.
Final Backfill and Grading
Complete backfill behind the wall with topsoil or existing soil (gravel should fill the bottom 12 inches, soil above). Grade the surface to slope away from the wall slightly. Plant or sod the area promptly to prevent erosion while soil is disturbed.
Pro Tips
Mistakes That Cause Walls to Fail
No Drainage System
This is #1. Water builds up behind walls and the hydrostatic pressure pushes them over. Every retaining wall needs a drainage pipe and gravel backfill. No exceptions.
Inadequate Base Depth
Frost heave will destroy a wall with a shallow base. In freeze-thaw climates, the base course must be buried below the frost line or at minimum 6–8 inches.
Stacked Joints (No Offset)
Stacking blocks with the seams lined up creates a structural weak point. Always offset each course by half a block, like bricklaying.
Using Soil Instead of Gravel for Backfill
Soil directly behind the wall compacts, retains water, and expands when frozen — all of which push the wall forward. Use clean gravel for the first 12 inches behind the wall.
Recommended Tools & Materials
These are the exact products I use on retaining wall projects — saves you from buying the wrong thing.
48" Professional Level
4-foot aluminum level. Critical for getting your base course perfectly level across the full wall run.
- ✓ Aluminum construction
- ✓ 3 vials (level/plumb)
- ✓ Accurate to 0.0005"
Landscape Block Adhesive
Weatherproof adhesive specifically for retaining wall cap blocks. Sets in 30 minutes, permanent bond.
- ✓ Weatherproof bond
- ✓ Works on all block types
- ✓ Sets in 30 minutes
4" Perforated Drain Pipe
100-foot roll. The drainage pipe that goes behind every wall. Prevents the hydrostatic pressure that causes wall failure.
- ✓ 100 ft roll
- ✓ Pre-sleeved in fabric sock
- ✓ Flexible, easy to route
Professional Landscape Fabric
Heavy-duty 4ft x 100ft roll. Wraps drainage stone and prevents soil migration into your gravel backfill.
- ✓ UV stabilized
- ✓ Water permeable
- ✓ Heavy-duty weave
Steel Hand Tamper
8"×8" steel plate tamper. For compacting the base trench and tight areas where a plate compactor won't reach.
- ✓ 8" x 8" steel plate
- ✓ Cushioned grip
- ✓ Professional grade
Mason's Line & Stakes Kit
500ft nylon layout string and stakes. Essential for keeping your wall face straight over a long run.
- ✓ 500 ft nylon line
- ✓ Weather-resistant
- ✓ Stakes included
Frequently Asked Questions
How tall can a DIY retaining wall be without a permit?
Most municipalities allow retaining walls up to 3–4 feet without a permit. Walls over 4 feet typically require engineering approval and a building permit. Always check your local codes — fines for unpermitted walls can exceed the cost of the project.
What is the cheapest material for a retaining wall?
Treated timber is typically the cheapest option ($5–$8 per linear foot), followed by concrete block ($15–$20). Natural stone is the most expensive but longest lasting. For DIY, concrete block offers the best balance of cost, durability, and ease of installation.
How important is drainage behind a retaining wall?
Drainage is the single most critical factor. Without it, water pressure builds behind the wall and will eventually cause it to lean, crack, or collapse — sometimes within a few years. Always install a perforated drain pipe and gravel backfill.
How long does a concrete block retaining wall last?
A properly built concrete block retaining wall with good drainage can last 40–60 years. The key factors are proper base preparation, adequate gravel drainage, and applying cap adhesive on the final course to prevent shifting.
Do I need to use rebar in a retaining wall?
For walls under 3 feet using interlocking concrete blocks, rebar is typically not required. For walls over 3 feet, or in areas with heavy clay soil or water pressure, filling cores with rebar and concrete significantly increases strength and longevity.