Retaining Wall Calculator

How to Build a Retaining Wall: Complete Guide

Retaining walls hold back soil on slopes, create usable flat areas, and add structure to landscapes. Here's everything you need to know about planning and estimating your project.

Retaining Wall Cost Comparison (2026)

Materials Checklist

• Wall blocks or material — the visible structure
• Cap stones — finished top course (flat, glued down)
• Base gravel — 6" deep compacted gravel beneath first course
• Backfill gravel — 12" wide behind wall, full height, for drainage
• Filter fabric — landscape fabric between gravel and soil to prevent clogging
• Drain pipe — 4" perforated pipe at base for water management
• Construction adhesive — for securing cap stones and top courses

Step-by-Step Overview

1. Excavate and level. Dig a trench 6" deep and 24" wide. Compact the soil.
2. Add base gravel. Lay 6" of compacted gravel. Level with a 2×4 and check with a level.
3. Lay first course. This is the most critical row — if it's not level, the whole wall won't be. Use a string line.
4. Stack remaining courses. Stagger joints (like brickwork). Add backfill gravel and fabric as you go.
5. Install drain pipe. Place perforated pipe at the base behind the wall on top of gravel.
6. Backfill. 12" of gravel behind wall, then soil on top.
7. Cap it off. Glue cap stones with construction adhesive for a finished look.

5 Retaining Wall Mistakes That Cause Failure

1. No drainage. Water pressure behind the wall is the #1 failure cause. Always use backfill gravel and a drain pipe.
2. Poor base preparation. A level, compacted base is critical. Skipping this causes settling and leaning.
3. Building too high without engineering. Walls over 4 feet need professional engineering. The forces increase dramatically with height.
4. Not stepping back. Walls should lean slightly into the hill (battered). Most block systems have a built-in setback per course.
5. Ignoring the surcharge. Heavy loads near the top of the wall (vehicles, structures, slopes) add lateral pressure. Factor this into your design.

When Do You Need a Permit or Engineer?

Rules vary by jurisdiction, but general guidelines:

Bottom line: If your wall is under 4 feet and not near a building or property line, you're usually fine for DIY. For anything taller, get professional help — the liability risk isn't worth saving a few hundred dollars.