ᐅ Retaining Wall 60 cm High – Is a Foundation Necessary?

Hello everyone,

I recently built a new house and am now filling my garden with topsoil. On the street side, I have 18-25cm (7-10 inches) of fill to reach the terrace level.
My plan is to build a retaining wall using masonry blocks.

I would like to have a foundation trench excavated as part of the filling process. It should be 50cm (20 inches) wide and about 20-30cm (8-12 inches) deep (topsoil layer).
Then I want to compact the sand and raise/compact it with a mineral mixture to height, and set the blocks in lean concrete with a back support.

Would this be sufficient for 2-3 courses of blocks (30-50cm / 12-20 inches + 10cm (4 inches) in lean concrete), or do I need a proper foundation of 40cm (16 inches) or more with pouring—even at this low height?

Best regards

There are two important points to consider:
1. Rigid at the top -> frost-resistant at the bottom. Otherwise, you will quickly get cracks. It is definitely not just 20-30cm (8-12 inches).
2. Support and integration. Using formwork blocks, you build a vertical wall. If it is meant to support, it must be properly integrated. Three rows of blocks are 60cm (24 inches), and you need an embedment depth of at least one third. 10cm (4 inches) of lean concrete is definitely not enough. Also keep in mind that you don’t want the retaining wall to protrude directly towards the street.

Thank you for the response,

So I will have to live with a 40 x 50 cm (16 x 20 inches) foundation. Does it have to be cast in concrete, or would a mineral mix be sufficient, applied and compacted in 20 cm (8 inches) layers? Then placing the bricks on top, set in lean concrete?

I’m asking because I need to go around my property once, which will be about 60 linear meters (200 linear feet). Concrete is like the new gold these days... cheaper options with more labor are welcome.

Best regards.

The embedment depth must be firmly connected to the formwork blocks. You can also use gravel underneath.

You could also build a dry-stone wall. You don’t need such a massive concrete foundation for that. We have a garden wall about 60cm (24 inches) high. It only has a gravel base underneath.
With the 18–25 cm (7–10 inches) height difference you have, the pressure is not that significant either.

WilderSueden schrieb:

The embedment depth must be firmly connected to the concrete blocks. You can also use gravel underneath.

Okay, how thick should the concrete layer be at a minimum? I was thinking of 40cm (16 inches) of gravel and then setting the blocks in 10cm (4 inches) of masonry concrete.