How to Build a Retaining Wall

This guide covers the essential steps for building a safe and durable block retaining wall under 4 feet tall.

Warning: Walls Over 4 Feet

Retaining walls taller than 4 feet (including the part below ground) are holding back immense pressure and require professional engineering and permits to be built safely. **Do not attempt to DIY a wall over 4 feet tall.** This guide is only for small, gravity-based landscape walls.

Phase 1: Planning & Excavation

Check Local Codes & Call 811:

Most jurisdictions require permits and professional engineering for walls over 4 feet tall. Call 811 before digging to have utility lines marked.

Excavate the Trench:

Dig a trench for your base layer. The trench should be deep enough for 6 inches of compacted base material plus half the height of your first block. It should be wide enough for your block plus 12 inches of drainage backfill.

Compact the Subsoil:

Use a hand tamper to create a solid, level foundation at the bottom of your trench. This is the first critical step for stability.

Phase 2: Base and First Course

Install and Compact the Base:

Add a 6-inch layer of crushed stone (paver base) into the trench. Compact it thoroughly with the tamper until it is completely level, both front-to-back and side-to-side. This is the most important step of the entire project.

Lay the First Course:

Place your first row of blocks on the compacted base. Use a level and mallet to ensure every block is perfectly level with its neighbors. The success of the entire wall depends on this first course being flawless.

Phase 3: Building, Drainage & Backfill

Stack Subsequent Courses:

Stack the next rows of blocks, staggering the joints like a brick pattern for strength. Most blocks have an interlocking lip that provides a natural setback.

Install Drainage Pipe:

Behind the first course, lay a 4-inch perforated drain pipe wrapped in landscape fabric, with the holes facing down. This will collect water and carry it away from the wall to prevent pressure buildup.

Backfill with Gravel:

As you build each course, backfill the 12-inch space behind the wall with clean drainage gravel (like 3/4" angular stone). This creates a crucial drainage zone.

Compact the Backfill:

Compact the gravel backfill behind the wall as you build up the courses.

Install Cap Blocks:

Once at the final height, secure the cap blocks or stones to the top course using a construction-grade concrete adhesive to finish the wall.