Key Takeaways
- 6-by-6 pressure treated lumber can be suitable for a wood retaining wall if the lumber is rated for ground contact.
- Building a wood retaining wall starts with planning the layout, checking building codes and HOA restrictions, checking for underground utilities and estimating your materials.
- Before you build a wood retaining wall, dig a foundation trench wide enough for the lumber and drainage material and deep enough for base gravel and half the height of the first row.
- Start building a low pressure treated retaining wall on a four-inch bed of level, compacted gravel, leveling the first row of lumber and securing it to the ground with rebar.
- Continue building the wall, cutting the lumber as necessary to stagger the joints and securing each row to the previous row.
- Line the trench behind the wall with landscape fabric, backfill behind each row with drainage gravel as you build, and fill any remaining space behind the third row with soil.
- When you finish your wood wall, you can landscape it and paint or stain it once the wood is dry enough according to the paint, stain or sealer manufacturer’s specifications.
Tools and Materials
Tools
Product costs, availability and item numbers may vary online or by market.
Plan Your Wood Retaining Wall
A Pressure Treated Lumber Wall
This project uses 6-by-6 pressure treated lumber:
- Pressure treated lumber is resistant to rot and insects.
- Pressure treated lumber for a retaining wall must be rated for ground contact.
- Actual lumber dimensions are 5-1/2 inches by 5-1/2 inches.
- Lengths of 8, 10, 12, 16 and 20 feet are available.
- Fasteners must be rated for use with pressure treated lumber.
Our guide to pressure treated lumber gives you tips on choosing and using this exterior-grade wood.
Planning and Layout Tips
Before you begin building a wood retaining wall:
- Check local building codes and follow all requirements, including specifications on height, drainage and when necessary, letting a professional design and build the wall.
- Check Homeowners Association rules for restrictions or required approvals.
- Call 811 to have underground utilities marked and adjust your layout if necessary.
- Make sure gutters don’t drain into retaining wall area.
- Measure and mark the layout with landscape stakes and mason line or marking paint.
How Much Lumber Do You Need for a Retaining Wall?
- Divide the length of the wall by the length of the 6-by-6s you’re using.
- Divide the total height of the rows by 5-1/2 inches, the actual height of the lumber.
- Multiply the results together to estimate the number of 6-by-6s you need.
- Add a couple of extra 6-by-6s to allow for cutting and future repairs.
Safety When Building a Wood Retaining Wall
Follow the use and safety instructions for your tools and materials, including the use of safety gear such as eye protection, work gloves, hearing protection and a respirator.
How to Build a Wood Retaining Wall
Every wall layout differs depending on factors such as location, the slope of your landscape and local building codes. Below is a general overview of key project steps for building a wood retaining wall. Adapt them to your landscape, local conditions and plan.
Step 1: Dig Out the Wall Area
The first row of the wood wall will be partially buried and rest on a bed of about 4 inches of compacted crushed stone.
- Dig out a foundation trench with a width that accommodates the lumber and a backfill of drainage gravel.
- Dig the trench deep enough to hold the crushed stone and allow half of the first row to sit below ground level.
- Compact the soil with a hand tamper and ensure the base of the trench is level.
- Spread the crushed stone along the bottom of the trench and tamp it level to the desired depth.
Before beginning any excavation, call 811 to check for underground utilities.
Step 2: Place the First Row of Lumber
For this project the wall is just three rows of 6-by-6 lumber. Rebar secures the first row to the ground and wood spikes secure the rows together. A steep slope or a higher wall may need T-shaped anchors, or deadman anchors, constructed of the lumber, behind the wall and fastened to the wall. Consult a professional for specifics on the best way to anchor your wall.
- Use a woodboring augur bit to drill pilot holes a foot in from each end of the 6-by-6s you use for the first row.
- Align the first 6-by-6 at the end of the trench.
- Add crushed stone underneath the lumber to raise it or use a drilling hammer and a piece of scrap wood to tap it lower.
- Drive rebar through the pilot holes and into the ground until the ends are flush with the top of the lumber.
- Align, install and secure the remaining 6-by-6s, ensuring they’re level.
Step 3: Backfill With Gravel
Gravel behind the wall helps water flow around the structure rather than allowing water pressure to build up and cause damage. Depending on your landscape, you might need perforated drainage pipe in addition to the gravel. Make sure any drainage directs water away from any nearby structure.
- Cut landscape fabric to run the length of the wall.
- Line the foundation trench with the landscape fabric, allowing the edges to overlap the lumber and the back of the trench.
- Pour drainage gravel over the fabric up to the height of the first row.
Step 4: Install the Second Row and Stagger the Joints
The joints of each row need to be staggered for stability, so you likely need to cut a piece of lumber in half to start and finish the second row. For this low wall, the rows are flush to each other. Depending on wall height, local codes and your site, you might need to set each successive row back slightly towards the slope or retained soil.
- Measure and mark halfway down the length of a 6-by-6.
- Cut the lumber in half with a circular saw and reciprocating saw.
- Treat cut ends of the lumber with a wood preservative suitable for the application and follow all the product instructions.
- Bore pilot holes a foot in from the ends of the lumber for the second row.
- Ensure the landscape fabric is out of the way, align the half-piece in place and drive wood spikes through the pilot holes and into the lumber below.
- Continue aligning, laying and securing the second row, ensuring the joints are staggered and ending with a half-piece.
- Once the second row is complete, backfill with gravel to top of the row.
To cut 6-by-6 lumber, mark a cut line aligned around all four faces. Use a circular saw to cut along the line on each face. Finish cutting through the remaining wood in the center using a reciprocating saw fitted with a long blade.
Step 5: Finish Building the Pressure Treated Retaining Wall
Complete the wall by installing the third and final row of lumber and backfilling the row.
- Secure the final row of 6-by-6s with wood spikes, ensuring they’re aligned and level, with the joints offset from those on the row below.
- Complete the gravel backfill, then fold the fabric over it and secure with landscape pins.
- Fill in the remaining space behind the final row using the soil you dug from the trench.
- Spread mulch or plant the area according to your landscape design plan.
Step 6: Paint or Stain and Seal the Wall
Once the lumber is sufficiently dry according to the coating manufacturer’s specifications, you have a few options for finishing the wood to improve moisture resistance and weathering:
- Seal the wood with a clear sealer to maintain a natural, rustic look.
- Apply an exterior stain and sealer product to accentuate a rich wood tone or create a rustic look of railroad ties or weathered lumber.
- Prime and paint the wall with exterior grade paint.
Find Everything You Need for a Wood Retaining Wall
Shop Lowes.com or visit your local Lowe’s to find lumber, gravel and other materials for your wood retaining wall. Plus, you’ll find all the tools you need for your project. Or talk to a Lowe’s Red Vest associate. They’ll help you find everything you need to do the job right and get professional results.