ᐅ Plot with a change in ground level – boundary wall between neighbors – foundation?

Hello!

I hope this is roughly the correct section for my question; if not, please feel free to move it.

Situation:
The neighbor’s plot is significantly higher than mine, and their garage was built just 20cm (8 inches) from the property line. Since the development plan actually requires that there be no sudden changes in ground level, the neighbor should have compensated for the height difference with a slope at about 45°. My garden level means there would be a roughly 1.5m (5 feet) wide slope here—of course, at the expense of their plot. So, we agreed that instead of the slope (and demolishing part of the garage...), the neighbor must build a retaining wall on the property line, which also ensures that drainage happens where it’s supposed to.

We have not yet set the final ground level on our side; we plan to lower it by about 70cm (28 inches). Now, the neighbor has dug a trench along the property line, poured concrete into it, and is building a wall on this foundation using hollow blocks that they also plan to fill with concrete later.

If I remove about 70cm (28 inches) of soil on my side, this will expose all but 30cm (12 inches) of their foundation. From my point of view, 30cm (12 inches) is not enough to support a roughly 1.8m (6 feet) high wall along with the adjacent garage and garden.

The neighbor disagrees. Therefore, my question: is there an online calculator somewhere that can determine the required foundation depth? I would rather not have the neighbor’s wall collapse on my children in a year... My construction company has also expressed concerns and does not want to carry out any further earthworks until the wall issue is resolved.

Thank you

He’s adding fill, you’re digging out, and he alone should pay for the wall. Stick to the development plan, leave the site as it is, and no one would have any concerns... As your neighbor, I wouldn’t do or say anything, but if you dig, build your own retaining wall, and leave my land alone. Karsten

Nordlys schrieb:
He adds soil, you remove it, he should pay for the retaining wall alone. Stick to the B plan, leave the terrain as it is, and no one would have any worries.... As your neighbor, I wouldn’t do anything or say anything, but if you dig, build your own retaining wall, and leave my land alone. Karsten

I’m afraid I didn’t express myself clearly, sorry for that.

I will leave his land alone. I will keep my terrain at the original ground level; currently, there is just a bit more soil from the basement excavation, which I will remove later. The garage at the property boundary stands about 100cm (40 inches) above the original ground level.

Nordlys schrieb:
Ok, so he piled up soil to create flat ground? Then that’s his problem. If he’s not reasonable and builds such wild structures there, the building authority has to intervene. That’s a mess. But he has to support it properly or slope it back. However, you’re also not allowed to dig deeper than the original ground level. That would then be your problem. Karsten

Our construction supervisor was just as pragmatic with us, but of course, that doesn’t lead to a good relationship with the neighbor. For me, the main concern was to find out how deep a foundation on his side has to be to actually stay stable and not collapse into my garden.

The development plan here is totally ridiculous anyway. On one hand, it allows terrain modifications of up to 100cm (40 inches) in both directions, but forbids steep terrain steps. At the same time, the garage must be built right on the property line. In practice, this leaves no choice but either to place the house below the terrain boundary or to raise the garage. The plots in this street are fairly level toward the back, but the street itself has quite a significant incline.

You agreed to have a wall built, and no one thought to discuss the heights? Did you decide only after your agreement that you want to excavate an additional 70cm (28 inches)?
In that case, the wall’s foundation would no longer be below the frost line. I don’t think that’s a good idea.

DReffects schrieb:
We have not yet finalized the ground level on our side; we still plan to lower it by about 70cm (28 inches). Now the neighbor at the boundary has dug a trench, poured concrete into it, and is now building a wall on the boundary on top of this foundation using hollow blocks, which he also intends to fill with concrete later.

I would say that any professional understands that this kind of rushed action is nonsensical from a procedural standpoint. You can only build on stable ground once your excavation and terrain shaping work is complete.

If I understand your description correctly, the foundation of the 1.8m (6 feet) high wall on his side is 1m (3 feet) deep in the ground, and on your side only 0.3m (12 inches)? Even if the height refers to your side and only 1.1m (3.6 feet) of the wall is visible above ground on his side (why so high?), it’s clear without calculations that this won’t hold.

Check the recent posts; we had a similar discussion here about a week ago regarding a semi-detached house, once with and once without a basement.

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