A retaining wall battles two main forces: “overturning” (tipping over) and “sliding” (being pushed forward by the soil). On a slope, these forces are amplified.

If you pour a smooth, sloping footing that follows the hill’s gradient, you create a slide. As the weight of the soil presses against the wall, the entire structure is liable to slide down that concrete ramp. Furthermore, gravity pulls vertically, meaning a sloped foundation does not distribute the weight of the wall evenly into the ground.

Therefore, the golden rule of retaining wall construction is simple: Footings must always be level horizontally.

What is a stepped footing?

Imagine a staircase carved into the hillside. Instead of one long, sloped trench, the foundation is dug in a series of flat, level steps that ascend the hill. The wall is then built upon these level terraces.

Why does that work?

1. Structural stability: Because each section of the footing is perfectly level, the weight of the wall is transferred directly downwards into the soil, maximising the soil bearing capacity.
2. Material efficiency: It minimises excavation. If you tried to keep a single level footing on a steep slope, you would have to dig incredibly deep at the top of the hill. Stepping allows the footing to rise with the terrain.
3. Versatility: This method works for almost all materials, whether you are using interlocking concrete blocks or traditional masonry.

Key design rules for stepped footings

If you are planning to build a retaining wall on a slope, you must adhere to specific overlap rules:

• The overlap: Where the footing steps up, the lower footing and the upper footing must overlap by a specific distance (usually at least the width of the footing).
• The step height: The vertical step should match the height of your building blocks (e.g., 215mm for standard blocks) so your courses remain level without messy cutting.

The undercover foundation: Soil and drainage

You cannot choose the right footing without considering what is underneath it. We in the UK deal with a variety of soil types, but clay is the most problematic.

The clay soil problem

Clay expands when wet and shrinks when dry. This movement can crack concrete footings. If you are building on clay, you may need a deeper trench filled with a sub-base of MOT Type 1 to prevent ground heave from shifting your wall. For a deeper dive, read our guide on how clay soil affects retaining wall stability.

Drainage is a non-negotiable

Water is the number one cause of retaining wall failure. A stepped footing can inadvertently act as a dam, trapping water behind the wall. So it is key to have a well planned and secure drainage system implemented. This can include:

• Perforated pipes: You must install a perforated land drain behind the wall at the footing level.
• Weep holes: If using concrete or brick, ensure weep holes are present to let water escape.
• Backfill: Never backfill with the soil you dug out (especially if it is clay). Use clean, crushed stone (20mm gravel).

For a comprehensive look at water management, see why drainage matters for retaining walls and how to get it right.

DIY or professional help? What is the safety threshold? 

We often see homeowners asking, “Can I build a retaining wall by myself?” The answer is yes, but know your limits. A failed wall is not just an eyesore; it is a liability. This is the most critical decision you will make, as other’s and yours safety can be compromised by making the wrong choice.

You can likely DIY if:

• The wall is under 1 metre in height.
• The slope is gentle.
• The soil is firm and dry.
• You are confident in your ability to mix concrete and use a laser level.

However, you MUST hire a structural engineer if:

• The wall is over 1 metre high.
• The slope is steep (more than 30 degrees).
• There is a load above the wall (a driveway, a shed, or a public footpath).
• The ground is unstable or waterlogged.

What is the concrete footing and depth I need?

While we cannot give you a structural design without seeing your site, there are general rules of thumb for small garden walls (under 1m).

• Width: The footing should generally be three times the width of the wall stem. If your block wall is 215mm wide, your footing should be roughly 650mm wide.
• Depth: The concrete footing depth should usually be equal to the wall width (e.g., 200-250mm minimum).
• Frost Protection: In the UK, the bottom of the footing must be at least 450mm below ground level to prevent frost heave.

If you are looking for cost-effective ways to manage this, you might check what is the cheapest way to build a retaining wall in the UK, but remember: skimping on footing depth is never a saving—it is a future repair bill.

Reinforcement: Do you need steel?

For a stepped footing on a slope, steel reinforcement (rebar) is highly recommended. It ties the steps together, preventing them from separating if the ground shifts.

• Longitudinal bars: Run steel bars along the length of the footing.
• Starter bars: If using certain concrete blocks, vertical bars (“starter bars”) should be set into the wet concrete footing to tie the wall to the foundation.

Common mistakes to avoid for sloped retaining walls

Even seasoned builders make mistakes with sloped footings. Here are three to watch out for:

1. The “slope pour”: As mentioned, pouring a sloped concrete ramp instead of steps. This invites sliding.
2. Inadequate overlap: Making the steps too short, so the upper footing rests on soft soil instead of the lower concrete section.
3. Ignoring the “Surcharge”: Forgetting that a car parked at the top of the slope adds massive pressure. See experts warn this one retaining wall error will cost you thousands.

Summary: A solid base for your project