How to Build Retaining Wall Stairs

Introduction

Building retaining wall stairs is a great way to create an attractive landscape feature while also dealing with steep elevation changes on your property. Retaining walls hold back soil and prevent erosion, allowing you to create flat yard spaces on a sloped lot. Integrating stairs into the wall provides access between different elevation levels in your landscape.

Constructing retaining wall stairs properly ensures that the finished stairs and walls are strong, stable and safe to use. While building these landscape structures requires some specialized masonry techniques, it can be a do-it-yourself project for homeowners with basic DIY skills.

This guide will walk through the complete process of planning and building retaining wall stairs step-by-step. We’ll cover how to choose the right materials, calculate layout, build a sturdy foundation, construct the stairs and walls, backfill properly and finish the project. Follow along to learn how to build retaining wall stairs that will transform your hilly yard into a beautiful, multi-level outdoor living space.

Choose Wall Blocks and Materials

The first step in any retaining wall stairs project is selecting the right landscape building materials. For the walls and stairs themselves, interlocking concrete retaining wall blocks are the best choice in most cases. These machine-made blocks are durably constructed to withstand the lateral pressure exerted by backfilled soil. Their interlocking design allows walls to be stacked vertically without requiring mortar.

The main options for interlocking retaining wall blocks include:

Split-face blocks – These have a rough, natural stone-like texture on the front face. They provide informal, rustic style.
Smooth-face blocks – As the name implies, these blocks have a smooth front face, giving a more refined, finished look.
Cobblestone blocks – These are molded to look like irregular rounded stones. They have an old-world, informal style.

Choose block color and texture to suit your landscape vision. Earthy beige and brown tones blend in naturally, while gray blocks have a more contemporary vibe. Block weight matters too – heavier blocks provide greater stability. Aim for blocks weighing at least 28 pounds. Heavier units are better for taller walls.

In addition to wall blocks, you’ll need the following supplies:

Gravel – As the wall and stairs foundation base. 3/4 inch gravel is commonly used.
Leveling pads – These specialized plastic or concrete pads provide a flat, level base for the bottom course of blocks.
Drainage materials – Perforated plastic drainage pipes and permeable geotextile filter fabric allow proper drainage behind the wall.
Base stabilizer – Products like road base or crushed stone compact and stabilize the gravel base layer.
Backfill soil – Small gravel backfill ensures proper drainage behind the wall.
Adhesive – An exterior-grade concrete adhesive secures capstones and steps.
Construction adhesive – Used to bind blocks together for added stability.
Landscape fabric – Prevents soil from washing out between block cracks.

Investing in the highest quality materials will ensure your retaining wall stairs stand the test of time. Don’t cut corners here.

Plan the Layout

Once you have the main building supplies lined up, it’s time to map out the layout. Grab a pencil and paper and draw the wall footprint. Here are some key considerations for planning:

Mark the elevation changes across the site using a string level. Calculate the total height you need to retain at the tallest section.
Walls over 4 feet tall may require geogrid soil reinforcement. Check your local building codes for exact height limits before designing your layout.
Determine the number of stairs needed based on the height. Most codes require stair risers to be between 4 to 7 inches tall. Wider, gentle-sloped stairs are more comfortable.
Account for the deeper area the stairs will require compared to the main walls. Add at least 18 inches of depth for each step.
Design the landing pad at the top as a flat area at least 36 x 36 inches wide. The bottom landing should be at least the width of the stairs.
For freestanding walls, plan the layout in a graceful curve or serpentine shape for better stability. Straight walls require sturdy corner buttressing.
Check for buried utilities or underground sprinklers and adjust the layout to avoid them if needed.

Make several sketches to optimize the look and function before finalizing the retaining wall stairs layout. Having a solid plan is crucial – it’s very hard to change the footprint once you start building!

Mark Out and Excavate

Now it’s time to transfer the layout from paper to your yard. Mark the footprint using spray paint or stakes and string:

Mark the front edge (toe) of the walls and stairs. Also mark the back edge, which should follow the slope contour.
Use a garden hose to lay out any smooth curves. Mark along the hose.
Use stakes and mason’s string to mark long straight segments. Leave the string lines up as guides.

Once the footprint is marked, excavate the area:

Remove all topsoil, plants and sod from the area. Excavate at least 6 inches below ground level.
The excavation should be wide enough to allow a stable gravel base (12-24 inches wide).
Excavate deeper at stair locations to allow for riser height, tread depth and gravel base.
Slope the excavation base away from the wall, about 1/4 inch per foot, for proper drainage.

Safety tip: Call 811 before digging to have any buried utilities professionally marked. Excavate carefully using a shovel once you get close to the marked depths of pipes or wires.

Install Gravel Base

Now it’s time to create the all-important gravel base:

Fill the excavated area with packed gravel (crushed stone or road base). Compact it in 4 inch layers using a hand tamper or plate compactor. The finished base should be 6-12 inches deep.
Make sure the gravel is flat, level and smooth. Check for level frequently with a 2×4 and 4 foot level.
Follow the footprint marks to slope the base away from walls about 1/4 inch per foot.

The gravel layer provides durable stability below the retaining wall stairs. Don’t be tempted to skimp on base materials or preparation – a poorly compacted base is the most common cause of retaining wall failure.

Install Base Pads and First Block Course

With the foundation base prepared properly, you’re ready to start stacking blocks. Proper methods here will ensure your wall doesn’t shift out of alignment as you build up:

First, secure specialized plastic or concrete leveling pads on the base using landscape adhesive or mortar. Level the pads side-to-side and front-to-back.
Position the first blocks tightly together on the leveling pads. Use shims or chips of gravel to adjust for level.
Check that the first course is perfectly level and aligned along the footprint using a 4 foot level and mason’s string.
If needed, gently tap blocks with a rubber mallet to fine tune alignment. Don’t proceed until the first course is perfectly straight and level.
Glue adjoining blocks using an exterior concrete adhesive. This provides extra stability.
Backfill behind the first course with drainage gravel, compacting as you go. This prevents the heavy upper courses from pushing the base out of alignment.

Follow these careful leveling methods with each course to keep walls plumb. Rushing the base and first courses can ruin the entire project quickly, so go slow. Measure, check and double check for level and alignment.

Build Up Retaining Wall

Once your base setup is perfect, the real construction fun begins! Here are some tips for properly building up retaining wall courses:

Alternate which side of each block protrudes out to give walls a straight, geometric appearance. Consistent block patterns also ensure even spread of pressure.
Use a string level to check vertical plumb every 2-3 courses as you build upwards. Adjust blocks as needed.
If your design incorporates curves, build the curves using blocks with a tapered, angled face. This avoids tight vertical gaps.
For corners and ends, alternate blocks so the seams between courses break in a staggered, overlapping pattern. This securely binds the entire wall together.
Apply exterior-grade concrete adhesive between courses to reinforce stability. Follow the adhesive label for cure times.
Backfill behind each row with gravel, compacting as you go. Wait 24 hours before building the next course to allow proper curing.

Proper structural techniques like these are essential to build retaining walls that won’t bulge or collapse under soil pressure. Take your time and do it right.

Build Stairs

Integrating stairs requires some specialized techniques:

Build stair sections on their own compacted gravel base, with deeper excavation for each riser’s height.
The bottom stairs can be built right into the main foundation leveling pads for a seamless look.
Steps are made using full-depth edge blocks designed for stair building. Glue them in place.
Front step edges often use decorative carved or rounded coping blocks with overhang for a finished look.
Each step rises 4-7 inches from the previous one. Build stair treads at least 12 inches deep and 36 inches wide.
Staircase walls must be well integrated with perpendicular retaining walls for stability. Wrap corners tightly.
Take exact height measurements for each riser to avoid finishing with uneven steps.

Building elegant staircases requires care and time. Don’t compromise on excavation depth, materials or measurements. Follow building codes for ideal riser height and tread depth.

Backfill Behind Walls

Once the stacked blocks are complete, proper backfilling is key to finish the walls:

Use free-draining gravel or crushed stone, compacting in 6 inch layers.
Stop backfilling 2-3 inches below the top of the blocks to allow space for capstones.
Install perforated drainage pipes at the base course, positioned to daylight downhill.
Wrap permeable filter fabric over the backfill to allow water drainage while preventing soil washout.
Take care to avoid heavy equipment near the wall, which can shift the foundation. Work from the sides or use hand tools.
Tamp down backfill gently. Aggressive compaction can push walls out of alignment.
Crown the backfill slope with a slight convex shape so water runs off the sides rather than pooling.

Proper drainage and compaction of backfill is crucial. Wall collapses are almost always caused by overly-wet backfill or poor drainage, so take the time to do it right.

Complete Finishing Touches

The final step is applying those all-important finishing touches:

Glue on capstones using concrete adhesive. This gives walls a clean, finished look with no exposed block edges.
To transition walls onto sloped yards, bury one edge of capstones at least 6 inches into the grade.
Build planting wells between courses to allow greenery within the wall face. This visually softens blank walls.
Stain or seal retaining wall blocks if desired to enhance color. Use masonry-grade products.
Add slope stabilization materials like jute mesh or landscaping rocks on any steep exposed soil slopes above walls.
Install low-voltage landscape lighting for a gorgeous nighttime look. Lights along stairways create dramatic focal points.

Take the time to properly finish and accessorize your retaining wall stairs. The right details can take the project from good to amazing.

Avoid Common Mistakes

While building retaining wall stairs takes time, the techniques are straightforward. Avoid these common pitfalls:

Random block placement patterns. Consistent, overlapping blocks spread pressure evenly.
No adhesive between courses. Unsecured blocks can shift and topple the walls.
Backfilling before curing adhesive. This can push fresh courses out of alignment.
Poor drainage. Using clay-heavy native soil for backfill invites erosion and heaving.
Aggressive backfill compaction. Light, even tamping is ideal to prevent wall shifting.
No filter fabric over backfill. Unprotected soil will gradually wash through block cracks.
Allowing heavy machinery near the wall edge. Even gentle bumps can impact stability.
No coping or edge restraint on stairs. Exposed block edges chip and spall from foot traffic.
Uneven steps. Carefully measuring each riser avoids tripping hazards.

Patience and attention to detail prevents almost all retaining wall problems down the line.

Retaining Wall Stairs Maintenance

Like any landscape construction project, some basic annual maintenance enhances both aesthetics and longevity:

Inspect walls and stairs for any shifting or bulging, which signals potential structural issues.
Re-level any blocks that settle or tilt out of alignment using shims.
Check for soil erosion behind walls or vegetation growing in cracks. Repair and re-plant as needed.
Re-apply stain or sealer to keep block color vibrant. Pressure-wash hard stains.
Clear any debris from weep holes and surface drainage channels to prevent clogging.
Ensure backfill areas drain properly after heavy rain. Fill any washed-out spots.
In winter climates, prevent soil heaving by allowing snow to insulate the ground until spring thaws.

With proper construction and annual maintenance, a retaining wall stairs project can provide safe, stable landscape functionality and beauty for decades. The upfront effort is well worth it for the impressive finished result!

Frequently Asked Questions

What size gravel is best for a retaining wall base?

3/4 inch crushed gravel or stone provides ideal retention wall base stability. The angular stone pieces interlock when compacted.

How far apart should I space landscape timbers for stairs?

For solid, safe stairs, space landscape timbers side-by-side with no gaps. Stagger seams between courses for strength. Pre-drill pilot holes to prevent splitting.

What is the best spacing distance between plants in a retaining wall?

Allow at least 1 foot of space between plantings in retaining wall planting wells. This prevents roots from compromising the stability of wall blocks.

Can I use native soil to backfill a retaining wall?

It’s best to use free-draining gravel or crushed stone backfill rather than clay-heavy native soil. This allows essential drainage behind the wall.

What is the best way to secure capstones on a retaining wall?

Applying a high-quality exterior concrete adhesive along the top course creates a permanent capstone bond as the adhesive cures.

How long should I wait between courses when building a retaining wall?

Let each course cure for 24 hours before stacking additional courses. This allows the adhesive and blocks to fully stabilize.

Are weep holes necessary in a garden retaining wall?

Weep holes are highly recommended to allow excess moisture to drain. Preventing hydrostatic pressure buildup helps avoid wall failure.

How do I prevent erosion on slopes above a retaining wall?

Use landscaping fabric, rocks, gravel, vegetation or other erosion-blocking materials on steep slopes above walls to prevent washout.

What kind of adhesive works best for securing retaining wall caps?

Look for adhesive specifically formulated for concrete and masonry. These provide the strongest, longest-lasting bond strength.

How far below frost line should I dig footings for retaining walls?

Dig wall footings below the frost line depth for your climate. This prevents dangerous frost heaving in winter from compromising stability.

Conclusion

Building retaining wall stairs transforms steep or uneven landscape areas into beautiful, functional spaces. Following proper planning, layout, construction, backfilling and finishing techniques results in sturdy, safe walls and stairs that can handle environmental pressures and everyday use. Patience pays off when building landscape structures from the ground up. The end result is an amazing DIY project you can enjoy and be proud of for years to come.