Retaining walls are essential for stabilizing slopes, preventing erosion, and creating usable outdoor spaces. However, their strength and longevity depend on proper construction, particularly the base, drainage, and backfill. A poorly built wall can lead to catastrophic failures like cracking, bowing, or even complete collapse. In this blog, we’ll break down the fundamentals of constructing a durable retaining wall and highlight common mistakes to avoid.

The Foundation: A Sturdy Base is Non-Negotiable

A retaining wall’s base is the foundation of its strength. Without a solid base, the wall can settle unevenly, lean forward, or even fail completely. Here’s how to get it right:

• Excavate below ground level – Dig at least 6-12 inches below grade for small walls and deeper for larger ones.
• Use compacted gravel – A 6-8 inch layer of clean crushed stone or gravel should be compacted thoroughly to provide a stable footing.
• Level the first row – The first course of blocks or stones should be perfectly level to ensure stability as the wall is built up.

Drainage: The Key to Preventing Failure

Water is the number one enemy of retaining walls…or any construction, really. Without proper drainage, hydrostatic pressure builds up behind the wall, leading to bulging, cracking, or even an “exploding” effect where the wall is pushed outward.

• Use 18+ inches of clean drain rock – This allows water to pass through freely rather than collecting behind the wall. Avoid using compacted soil as backfill, as it retains moisture.
• Install a perforated drain pipe (drain tile) – Placed at the base of the wall, this pipe directs excess water to a safe outlet, preventing water pressure from building up.
• Slope the drain tile – The pipe should be slightly pitched to guide water away from the wall rather than pooling behind it.

What Happens When a Wall is Built Incorrectly?

Failure to follow these best practices can lead to:

• Hydrostatic Pressure – Water buildup behind the wall exerts pressure that can cause it to bulge or break.
• Structural Damage – Homes or adjacent structures can be affected if a retaining wall shifts or collapses.
• Collapse & Erosion – If the base isn’t stable, the wall can sink or topple over time, leading to property damage and safety hazards.
• Blowouts (“Exploding” Walls) – If pressure builds up too much, individual blocks or sections of the wall can be forcefully pushed out.

DIY Tips for Building a Retaining Wall

If you’re considering building a small retaining wall yourself, here are a few additional tips:

1. Choose the right materials – Concrete blocks and natural stone or boulders are common choices. Each has different installation methods and drainage needs.
2. Step back the wall slightly – Leaning the wall slightly back into the slope helps counteract the pressure behind it.
3. Use geogrid for taller walls – If your wall is taller than a couple feet, reinforcing it with geogrid fabric will add extra stability.
4. Check local codes – Some areas require permits or engineering approval for walls over a certain height.

A well-built retaining wall enhances your landscape and protects your property. By ensuring a solid base, proper drainage, and high-quality materials, you can create a long-lasting structure that stands the test of time. If you’re tackling a larger project, consider consulting a professional to ensure safety and durability.