How to Plan for Proper Drainage in Your Retaining Wall Installation

Installing a retaining wall is a great way to enhance your landscape’s stability and long-term appeal. While selecting the right retaining wall blocks is an important step, planning for proper drainage is just as crucial. A well-designed drainage system will keep your wall strong, prevent water buildup, and ensure long-lasting performance.

If you’re in the planning phase of your project, now is the perfect time to think through how your retaining wall will manage water. Below, we’ll walk through key tips to help you prepare for a smooth installation and a well-draining, durable retaining wall.

Plan Your Drainage Strategy Before Starting

Many DIY enthusiasts and even some professionals overlook drainage until after the wall is built. However, incorporating a drainage plan from the start makes the process much easier and ensures long-term stability.

Before you begin, consider these key questions:

• Where does water naturally flow in your yard?
• Will the wall retain soil on a slope that directs water toward it?
• Do you need to redirect water using a drain pipe, spillway, or weep holes?
• How much space is required behind the wall for backfill and drainage materials?

Taking these factors into account ensures your retaining wall will manage moisture effectively, preventing future drainage problems. Now, let’s take a closer look at how proper location, materials, and installation techniques contribute to a well-draining, long-lasting wall.

Choose the Right Location for the Wall

The location of your retaining wall plays a key role in its long-term performance. To reduce the risk of water buildup, position your wall where water naturally drains away rather than collects. If your site naturally retains moisture, consider making landscape adjustments before installation to redirect excess water.

If a low-lying area is unavoidable, there are still effective ways to protect your wall. Installing a French drain can help channel water away, while grading the surrounding landscape can further improve drainage. With the right planning and adjustments, your retaining wall can remain strong and stable, regardless of the terrain.

Excavate Beyond the Wall’s Footprint

Proper excavation is one of the most important steps to ensure both stability and effective drainage. Many first-time builders assume they only need to dig a trench as wide as the wall blocks,  but a retaining wall requires additional space for backfill and drainage materials.

• To ensure optimal drainage, excavate a minimum of 12 inches behind the wall to make room for compacted gravel and a drain pipe if needed.
• Excavate 12 inches below ground level, to accommodate 6 inches of base material and 6 inches of block embedment.
• It’s important to keep the base level during excavation, as an uneven foundation can cause settling issues that affect the drainage system over time.

Taking these steps upfront makes installation smoother and helps prevent water-related damage in the future.

Select Appropriate Base and Backfill Materials

The right materials beneath and behind your retaining wall allow water to pass through freely instead of becoming trapped.

• For the foundation, use crushed stone (¾ inch or larger) rather than sand or soil, which can compact and slow water movement. We recommend a 6 inch depth for the base under the first course of wall blocks.
• The best backfill material is clean, crushed gravel (¾ inch in size) since it allows for easy drainage. Avoid pea gravel or soil, which hold moisture and can lead to water buildup.
• A non-woven geotextile fabric behind the wall will help keep the gravel backfill clear of soil buildup, ensuring efficient drainage.

By choosing the right materials, you set up your retaining wall for long-term success, ensuring water flows efficiently away from the structure.

Plan for Drain Pipe Placement Before Laying Blocks

For walls taller than 2 feet, incorporating a perforated drain pipe is advisable. Proper installation is essential for effective drainage.

• Position the drain pipe at the base of the wall, just above the foundation layer.
• Ensure the pipe has a consistent slope (at least 0.5%) to guide water away from the wall.
• Protect the pipe with drain sleeves or filter fabric to prevent soil infiltration.
• Extend the drain pipe to a safe discharge point, such as a low area in your yard or a drainage ditch.

Planning the drain pipe layout before assembling your wall ensures a smoother installation process and reduces the need for adjustments later.

Ensure Proper Compaction at Every Stage

A well-compacted base and backfill prevent shifting, erosion, and drainage failure. If the materials settle unevenly after installation, they can compromise water flow and cause instability.

To avoid this, compact the base layer thoroughly before laying the first row of blocks. As you backfill, add gravel in 4-inch layers and compact each layer before adding more. This gradual approach ensures even weight distribution and prevents air pockets from forming.

Using the right tools—such as a hand tamper or plate compactor—will help achieve proper compaction for a wall that remains stable and well-draining over time.

Consider Additional Drainage Features for Extra Protection

Each landscape is different, and in some cases, additional drainage solutions may be beneficial. If your yard has heavy rainfall or retains excess moisture, extra safeguards can help protect your retaining wall from long-term water damage.

• Weep holes can be installed in certain retaining wall designs to allow excess water to escape gradually.
• Surface drainage solutions—such as adjusting the grade above your wall—help direct rainwater away from the wall instead of toward it.
• In some cases, spillways or specialized wall drains can be installed to guide water through the wall instead of letting it collect behind it.

By tailoring your drainage plan to your specific property needs, you can ensure your retaining wall remains strong and reliable for years to come.

Double-Check Slope and Drainage Before Finalizing Installation

Before finalizing your retaining wall, take a few extra minutes to confirm that your drainage system is working as intended. This step ensures proper water flow and helps protect your investment for years to come.

Test for proper drainage by:

• Pouring water behind the wall and observing how it drains. If it pools instead of flowing away, adjustments may be necessary.
• Ensuring drain pipe outlets are clear and unobstructed.
• Checking that backfill is evenly compacted to prevent settling over time.
• Confirming that the surrounding landscape slopes away from the wall to guide water in the right direction.

By reviewing these details before completing installation, you can be confident that your retaining wall will perform at its best—keeping your landscape secure, well-drained, and built to last.

A Retaining Wall That Stands the Test of Time

Proper planning is the key to a long-lasting retaining wall. By considering drainage before breaking ground, you can build a structure that remains strong, stable, and free from water-related issues for years to come.

Ready to start your project?

Western Interlock provides premium retaining wall blocks and expert guidance to help you build with confidence. Explore our product selection today, or visit our DIY with WI page for more professional tips and tutorials.