Building from the Ground Up: How to Size the Base of a Retaining Wall

When Marco bought the little hillside property on the edge of town, he saw potential. A terraced garden. A patio with a view. Maybe even a waterfall someday. But before any of that could happen, he needed to tackle the slope that leaned a little too eagerly toward his back door.

That’s where the retaining wall came in.

Marco had watched a dozen videos online and read all the tutorials he could find, but one question kept coming up: how wide should the base of his retaining wall be?

He learned something important early on—it’s not one-size-fits-all.
A rule of thumb said the base width should be at least one-third of the wall’s height, but that was just a starting point. For gravity walls under 4 feet high, he found that a base half the height was a solid, safe choice.

So when Marco planned his first 4-foot wall to hold back part of the slope near his garden, he chose a base width of 2 feet—50% of the height. Simple enough, right?

But as the project grew—because projects always do—he realized that parts of the slope were closer to 8 or even 10 feet high, especially where he wanted to build a sitting area. That changed everything.

He learned that walls between 4 and 10 feet need a base width between 40% and 60% of the height—and sometimes more. And when you’re dealing with walls over 10 feet, you’re in engineering territory.

Marco didn’t want to take chances.

The soil on his land was loose and sandy—not ideal. There was also a slight surcharge load from the nearby shed and slope above. That meant the base needed to be even wider for safety.

So for the taller section, Marco widened the base to 6.5 feet for a 10-foot wall—almost two-thirds of the height. He also made sure to:

• Use compacted gravel for a stable foundation
• Dig the trench deep enough to bury at least one full course of blocks
• Install proper drainage behind the wall to prevent pressure from water buildup
• Check local codes to ensure compliance
• And where he needed it, he brought in a structural engineer to double-check his design

He also learned about cantilever walls—larger retaining walls that rely on a reinforced base and footing to “push back” against the pressure of the soil. While Marco didn’t use this type, he understood why wider bases mattered even more in such designs.

In the end, the wall wasn’t just strong—it was smart.

It held the hill back. It gave him a level space to build. It framed his garden beds beautifully. Most of all, it gave Marco peace of mind.

Because what he learned was simple: the strength of any wall starts at the base.
And the best way to build a wall that lasts?
Understand the soil. Respect the load. And build from the ground up—with intention.

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