Is staircase DIN 18065 mandatory or not?

We have spruce planks visible completely inside and outside

I would only do that inside as an accent.

so that you don't get the feeling that the walls are oppressing you... [...] In general, the furnishings have to be chosen differently when you have wooden walls, because for example not every parquet or furniture decor matches the walls.

Exactly because of that.

We also have cross points starting from 4.50m, which we basically use as "room dividers". They only come in 15cm inside and outside... But they were necessary, otherwise the risk of warping would be too high...

That is related to the traditional construction method and is structurally eliminated in modern variants.

I am talking about a log house made of planks, inside to outside: 10cm spruce/20cm blown-in insulation/5.8cm spruce.

You can do that, but it is state of the art from about a handful of timber construction fairs ago.

Many things that were listed as client-side in the construction performance description, about which one only later realized how complex they actually are. And of course completely different tools.

Sure, you can't do any filling, the dowels are different, but otherwise?

The walls are already prefabricated and are almost settlement-free due to bracing.
The wall is designed as a composite wall. Plank with rafters, insulation and then the installation layer.

So panel construction – what does "plank with rafters" mean?

I’m linking the post by or have you already found it yourself?

https://www.hausbau-forum.de/threads/grundrissplanung-einfamilienhaus-massivholzbauweise-140qm-in-niedersachsen.44745/#post-611989

As long as you only use it for yourself, it can hardly bother anyone. But if a child ever falls, it looks different again. The architect pointed you to the regulation. Then he is out of liability.

My son fell down our stairs and broke his arm. In the health insurance questionnaire, they asked whether the stairs comply with the building regulations at the time of construction. I answered that I can only respond once they send me the regulations from 150 years ago.

I can already imagine that in cases of very high consequential costs (disability, need for care, death), insurers will do everything to avoid paying.

We visited various staircase studios today. All consultants said that we must comply with the DIN, but the building authority will not really pay attention to it. Regarding the 1st escape route, the standard must also be observed and a minimum width of 80 cm must be maintained. Ultimately, everyone advised us to choose a 1/4 turn staircase. This is, of course, somewhat steeper in order to meet our wishes. However, it is really, really very comfortable for us.

I don't understand you. Here everyone tells you the staircase is too steep. The architect and the staircase construction companies tell you to comply with the standard.

This is of course somewhat steeper to meet our wishes. But for us really really very comfortable.

But you do make it a bit steeper then??

May I ask how old you are? Until my late 30s, I also thought that stairs only start causing problems when you are over 70. I am now in my mid-forties and notice that stairs are less fun. My wife has noticed it for longer due to damaged cruciate ligaments. On the one hand, it is due to the eyes, which develop funny quirks after 25 years of monitor exposure, so that depth of field – especially in non-laboratory-type light – no longer works well. On the other hand, the muscles, despite or because of training and slow regeneration, no longer want to work as they used to. After an 80 km bike ride, I walk the next day as if after a Tour de France mountain stage. The last thing I would build in my house is a "oh it will probably be fine stair" – neither for design nor cost reasons. The DIN standard actually makes sense, as it is based on experience and ergonomics.