If you have a sloped garden that’s difficult to plant on or manage, building a retaining wall can be the perfect solution. This guide will show you how to build a retaining wall on a slope, turning an awkward hill into usable, beautiful terraces.
A well-built wall holds back soil, prevents erosion, and creates flat areas for planting or seating. It’s a project that adds both function and value to your landscape. With careful planning and the right materials, you can tackle this job yourself over a weekend or two.
How to Build a Retaining Wall on a Slope
Before you dig in, it’s crucial to understand the basics. A retaining wall must resist immense pressure from the soil and water behind it. Poor construction leads to bulging, cracking, or collapse. The key principles are a solid base, proper drainage, and careful stacking.
Planning and Design Essentials
First, check with your local building department. Many areas require permits for walls over a certain height, typically 3 to 4 feet. They’ll have codes you must follow for safety. Ignoring this step can lead to fines or being forced to tear down your work.
Next, choose your material. Options include concrete blocks, natural stone, timber, or bricks. For DIYers, interlocking concrete blocks are often the easiest. They’re designed for this purpose and don’t need mortar.
Determine your wall’s height and layout. Use stakes and string to mark the front line. For a curved wall, use a garden hose to outline a shape you like. Remember, the wall will be set back into the slope, so you’ll need to excavate.
Tools and Materials You’ll Gonna Need
Gathering everything beforehand saves time. Here’s a typical list:
* Materials: Retaining wall blocks, gravel (paver base), drainage pipe, landscape fabric, construction adhesive.
* Tools: Shovel, spade, wheelbarrow, hand tamper or plate compactor, level, rubber mallet, tape measure, safety glasses, gloves.
* Optional but helpful: Masonry saw for cutting blocks, string line, line level.
Step-by-Step Construction Guide
Now, let’s get to the hands-on work. Follow these steps in order for a strong, lasting result.
Step 1: Excavate the Trench
Start by digging a trench where the first course of blocks will sit. This trench should be wider than the blocks themselves.
* For most blocks, dig about 8 inches deep.
* The width should be the block width plus 6 inches for working room.
* The trench bottom must be level from side-to-side. It can follow the slope of the ground (run parallel to it) for a stepped wall effect.
Step 2: Create a Gravel Base
A compacted gravel base is non-negotiable. It provides stability and prevents frost heave in colder climates.
* Fill the trench with about 4-6 inches of gravel.
* Use a tamper to compact it firmly and completely.
* Check for level again, adding or removing gravel as needed. This base must be perfectly level.
Step 3: Lay the First Course
This is the most important layer. If it’s not level, the whole wall will be off.
* Place your first block in the center of the trench. Tap it down with the rubber mallet.
* Continue laying blocks end-to-end along the trench.
* Constantly check for level along the top and from front to back. Use your string line as a guide for straightness.
Step 4: Install Drainage
Water pressure is a wall’s biggest enemy. Proper drainage relieves this pressure.
* Behind the first course of blocks, lay a perforated drainage pipe. Position it so the holes face down.
* Ensure the pipe has a slight slope (about 1 inch for every 8 feet) to carry water away to the sides or a safe outlet.
* Backfill behind the blocks with more gravel, covering the pipe completely.
Step 5: Stack Subsequent Courses
Now you can build upward. Most interlocking blocks are designed to stagger easily.
* Start the second course with a half-block to create a staggered pattern, like bricks. This adds strength.
* Place each new block so its joints don’t align with the block below it.
* Use a level frequently to ensure each block is level and the wall is leaning slightly back into the slope (called “batter”), if the block design calls for it.
Step 6: Backfill and Compact
As you build each course, backfill behind the wall with gravel up to the height of that course. Tamp the gravel down firmly before adding the next layer of blocks. This provides additional drainage and support.
Step 7: Cap It Off
The final step is installing capstones. These are special flat blocks that lock the wall together and provide a finished look.
* Secure capstones with construction adhesive recommended for masonry.
* This prevents them from being knocked or kicked off.
Finishing Touches and Planting
Once the wall is complete, you can backfill the area behind the top gravel layer with soil. Place landscape fabric between the soil and gravel to prevent clogging. Now, the fun part begins—planting!
Choose plants that suit your climate and light conditions. For the terraced areas, consider shallow-rooted perennials, herbs, or ground covers. At the wall’s base, trailing plants like creeping phlox or sedum can soften the edge beautifully.
Common Mistakes to Avoid
Even experienced gardeners can slip up. Watch out for these pitfalls:
* Skipping the gravel base: This leads to settling and instability.
* Ignoring drainage: This is the fastest route to a failed wall.
* Not checking level constantly: A small error magnifies as you build up.
* Using the wrong adhesive: Only use adhesive meant for outdoor masonry work.
* Forgetting to compact backfill: Loose soil settles and creates gaps.
FAQ Section
How deep should the base be for a retaining wall on a hill?
For most walls under 4 feet, a 4-6 inch compacted gravel base is sufficient. The deeper and more stable your base, the better the wall will handle the slope’s pressure.
Do I need drainage behind every retaining wall?
Yes, almost always. The only exception might be a very short, single-course wall in extremely well-drained soil. It’s much safer to always include a gravel backfill and a drainage pipe.
What is the easiest type of retaining wall to build yourself?
Interlocking concrete blocks are generally the easiest for DIY. They are uniform, often don’t need mortar, and are engineered for stability, which makes building on a slope more straightforward.
How do you cut retaining wall blocks?
Use a masonry blade on a circular saw or a specialized masonry saw. Always wear safety glasses and a dust mask. Score the block on all sides before making the full cut.
Can you build a retaining wall on a steep slope?
Yes, but it requires more planning. You may need to build a series of shorter, terraced walls instead of one tall one. For very steep slopes, consulting a professional is highly recommended for safety reasons.
Building a retaining wall is a rewarding project that changes your garden’s functionality. Take your time with planning and the base, and you’ll have a structure that serves you well for years to come. Remember, its always better to double-check your level and drainage than to have to rebuild later.