How To Build a Wood Retaining Wall

A timber retaining wall is a great way to create level areas in a sloped yard, prevent soil erosion, and add visual interest to your landscape. This project requires careful planning and execution. In this guide, we’ll walk you through how to build a wood retaining wall similar to the play area This Old House landscape contractor Roger Cook demonstrates in the video above.

Planning Your Timber Retaining Wall

Before starting construction, determine the wall’s location, height, and length. Also, take time to research and obtain any permits you may need for the project.

Choosing the Right Location

Select a location for your retaining wall that will effectively hold back soil and create the desired level area. These factors should influence your decision:

• Accessibility and maintenance: Set things up for easy access to construction equipment during installation. Plan for future maintenance needs, such as wood treatment or replacement. Consider incorporating steps or terraces for improved accessibility, if needed.
• Drainage patterns: Identify natural water flow directions on your property. Avoid areas prone to water accumulation or flooding and plan for drainage systems, such as weep holes and backfill materials. You might also consider incorporating a French drain or other drainage solutions behind the wall, as you see in the video. 
• Enhancing aesthetic appeal: Consider sight lines and views from different areas of your property. Use the wall to create distinct outdoor rooms or functional spaces. Plan for complementary plantings or decorative elements to soften the wall’s appearance.
• Long-term property plans: Consider future landscaping or construction projects that may impact the wall’s location. Also, consider how the wall might affect property value and curb appeal.
• Proximity to existing structures and utilities: Maintain safe distances from buildings, fences, and other structures. Locate and mark underground utilities, including water, gas, and electrical lines, before excavation. Consider the impact on tree roots and existing vegetation, and make sure the wall doesn’t interfere with property lines or easements.
• Soil type and stability: Assess the soil composition in the area to know whether it’s clay, sand, or loam. Conduct soil tests to determine load-bearing capacity and strength. Consider potential soil expansion or contraction due to moisture changes. Evaluate the slope angle and height to make sure the wall can withstand the lateral earth pressure.

Determining Wall Height and Length

The height and length of your timber retaining wall will depend on your property’s specific needs. Generally, it should not exceed 4 feet tall without professionally engineering the retaining wall. Carefully measure the area to determine the required length of your wall. Check for accuracy to minimize material waste and avoid structural issues later.

Obtaining Permits

Local regulations often require permits for retaining wall projects, especially those exceeding a certain height or located near property lines. Check with your local building department to determine the specific requirements for your area. Obtaining the necessary permits will help you avoid potential fines and make sure your wall meets safety and building standards.

Materials and Tools Needed for a Wood Retaining Wall

Gather the right materials and tools for a successful timber retaining wall project. A well-prepared materials list will streamline your building process and help avoid interruptions.

Materials

• 3/4-inch crushed stone to promote drainage
• 4-inch perforated drainage pipe for efficient water flow
• Landscaping filter fabric to prevent soil from clogging the drainage system
• Landscaping screws for securing timbers
• Pressure-treated landscaping timbers
• Rebar spikes (four feet long, 1/2-inch diameter) for anchoring timbers
• Wood preservative

Tools

• 6-foot level and torpedo level
• Circular saw for cutting timbers to length
• Drill with a 9/16-inch spade bit for pre-drilling holes
• Foam paintbrush for applying wood preservative
• Hand tamper to compact soil and stone
• Impact driver to install screws
• Shovel for digging trenches
• Sledgehammer for driving rebar spikes
• String line and stakes to mark the wall’s location
• Wheelbarrow for transporting materials

Preparing the Site

Proper site preparation sets the stage for a stable and long-lasting retaining wall. Follow these steps:

1. Mark the wall’s location using wooden stakes and nylon string.
2. Stretch a level line near the ground to represent the top of the first course of timbers.
3. Dig a trench six inches deep along the wall’s perimeter.
4. Use a hand tamper to compact the bottom of the trench thoroughly.
5. Add 3/4-inch crushed stone to the trench and compact it with the hand tamper.

Installing the First Course of Timbers

The first course of timbers forms the foundation of your retaining wall. Check for a level and secure base for the wall’s overall stability. Here’s how to install it:

1. Drill 9/16-inch diameter holes in the first of course timbers, spaced about two feet apart.
2. Place a timber in the trench and check it’s level using the 6-foot and torpedo levels.
3. Secure the timber by driving 4-foot rebar spikes through the pre-drilled holes and into the ground using a sledgehammer.
4. Cut timbers to length as needed using a circular saw. Apply wood preservative to all freshly cut ends with a foam brush.
5. Measure across the width of the wall to make the side timbers parallel, making necessary adjustments.

Building Up the Retaining Wall

After establishing the foundation, building up your retaining wall involves careful layering and securing of timbers. Follow these steps:

1. Place the second row of timbers on top of the first course. Stagger the end joints by at least four feet for added strength.
2. Secure the second course to the first using landscaping screws and an impact driver.
3. Continue adding courses, consistently checking for level and plumb alignment.

Installing a Drainage System for Your Retaining Wall

Then, install a drainage system behind the wall to prevent water buildup by doing the following:

1. Pour 3/4-inch crushed stone behind the wall.
2. Cover the hillside with landscaping filter fabric.
3. Lay a perforated drainage pipe on top of the stone, sloping it toward the front of the wall for proper drainage.
4. Cover the pipe with more crushed stone and wrap the filter fabric over it.

Adding Structural Support to Your Retaining Wall

To reinforce the stability of taller structures, incorporating “deadmen” or tie-backs is essential. Here’s how to do it:

1. Create T-shaped deadmen from short lengths of landscaping timber.
2. After installing the third course of timbers, dig T-shaped trenches into the hillside behind the wall.
3. Place the deadmen in the trenches, aligning them flush with the wall.
4. Secure each deadman to the retaining wall using two landscaping screws.
5. Drive two rebar stakes through pre-drilled holes in the deadman to anchor it to the soil.
6. Install one deadman every six to eight feet along the entire length of the wall.

Retaining Wall Finishing Touches

Complete your timber retaining wall with these final steps for a polished and professional finish:

1. Continue building up the wall to the desired height, securing each course with landscaping screws.
2. Backfill behind the wall with soil, compacting it in layers to prevent settling.
3. Grade the area in front of the wall for proper drainage away from the structure.
4. Cover the ground in front of the retaining wall with two to four inches of bark mulch for a polished look.

Timber Retaining Wall Maintenance and Care

Regular maintenance will help your timber retaining wall last longer. Here are some best practices to follow:

• Check the drainage system to make sure it’s functioning properly.
• Inspect the wall annually for signs of shifting, bulging, or decay.
• Reapply wood preservative to exposed ends every few years.
• Replace any damaged or rotting timbers promptly.