ᐅ Partition wall thickness in a duplex house. Structural engineer specifies 17.5 cm.

kamda schrieb:
We are currently leaning towards the 17.5 to gain about 7 cm (3 inches) more interior width.

That will be sufficient, but the premise seems unsuitable as a priority to me.

kamda schrieb:
Yes, exactly, our neighbor is known to us and we have already exchanged information. He will also build with a basement. However, he is still in the phase of "gathering quotes." We plan to start in March (depending on the weather).

If it remains "without basement" for you as starters and "with basement" for him as the latecomer, then please give him my urgent advice to start his basement work simultaneously with you. There isn’t that much flexibility in the contracts up to this height, so he won’t be able to gain much advantage, but the protection of your building during his excavation is not free either.

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kamda schrieb:
We are now wondering whether the additional 7cm (3 inches) provide significantly better sound insulation or if we would rather enjoy the 7cm (3 inches) extra interior width.

For multi-layer partition walls, the thickness of the separating gap is more important than the thickness of the individual wall panels. At least 50mm (2 inches), preferably 70mm (3 inches). The whole construction must be executed cleanly, free of structure-borne sound bridges.

11ant schrieb:
If you, as beginners, stick to building without a basement and he, as the latecomer, builds with a basement, then please give him my strong advice to start his basement at the same time as you. There isn’t that much variation in the allocations up to this height, so he can’t really gain much by delaying, but the protection of your building during his excavation is certainly not free.

We will also be building a basement. Yes, that is correct. We will bring up this point. We are somewhat concerned about the shoring anyway. Does it work well? Meaning, without later cracks or similar issues in our house?

MayrCh schrieb:
For multi-layer partition walls, the thickness of the separating joint is more important than the thickness of the individual wall panels. At least 50 mm (2 inches), preferably 70 mm (3 inches). The whole thing must be executed cleanly (= free of structural sound bridges).

Thank you for the advice! Does this mean that we are practically not building directly on the property boundary, but offset by about 3.5 cm (1.4 inches) with a 7 cm (2.8 inches) separating joint?

kamda schrieb:
Does this mean that we are practically not building exactly on the property boundary, but offset by 3.5 cm (1.4 inches) with a 7 cm (2.8 inches) gap?

I have no idea how you are building. Your architect should tell you.
With two semi-detached houses planned and built independently, it becomes interesting what your neighbor plans and how they implement it. You can try as much as you want, but if they cut corners, it’s all for nothing.

kamda schrieb:
We are also going to build a basement.

Then it’s not such a big deal. Only if you build without a basement on your side would they have to take extra care to avoid creating a leaning tower like Pisa on your property. Still, I stick to my suggestion—even if not as a strict recommendation—to practice synchronized swimming up to the basement ceiling. Above that, there’s still plenty of opportunity to save a bit on each trade.

kamda schrieb:
Does that mean we’re practically not building right on the property line but offset by 3.5 cm (1.4 inches) with a 7 cm (2.8 inches) gap?

MayrCh schrieb:
You can prepare as much as you want, but if the builder messes up, it’s all for nothing.

I can only agree: to be safe, plan on completing the entire separation gap on your side of the property.

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Important sentence: sound insulation according to recognized technical standards should be explicitly included in the contract.
Pay special attention to impact sound bridges in the areas of the ring beam, floor slab/screed, and external wall/render.
As a planning goal, an increased sound insulation level of 67 dB should be aimed for. Ask your architect if they can guarantee this.
Referring only to DIN 4109 is not sufficient, as that standard requires just 57 dB, which is an outdated minimum requirement. Be cautious with continuous floor slabs; this should be avoided. Make sure to have the above sentence fixed in writing!
Once the houses are built, it will be too late and you may face conflicts with the neighbors. Make sure to involve the neighbors regarding sound insulation.
Good luck with your house construction!