Which building regulations make new constructions so expensive?

I never claimed that it would be twice the effort. But it is also not completely irrelevant whether I stick 10 or 14cm to the facade. A few additional costs do arise.

Building regulations do not make construction expensive. At least not directly. There are, as some have aptly described here, items that make you shake your head, but the basic building regulations have not changed for many, many years. There has only been a moderate tightening of the energy requirements, but as already mentioned, 14 or 10 cm ETICS make no big price difference. The majority of the cost increases simply come from higher procurement costs, higher wages, and the usual supply and demand game. And finally, it is the wishes of the builders. Does it have to be KNX? Do the tiles have to be 120x120 cm? Does the living space have to be 160 sqm for a 2-person household? Or or or

Building regulations are not what makes building expensive.

Interestingly, however, this is regularly cited by the construction and real estate industry as the reason for increased building/purchasing/rental costs. But I have never believed that either.

Interestingly, it is the justification regularly criticized by the construction and real estate industry for the increased construction/purchase/rental costs.
But I have never believed it either.

It needs to be viewed a bit more nuanced. The increased rental costs result from the increased construction costs. Except for locations in rural areas, you already need new-build rents of at least €12-15/sqm for a project to be economically viable. In the Ruhr area, for example, this is virtually impossible. That is why there is also a severe housing shortage there (for anything other than junk apartments).
The issue of building regulations and political regulations rather concerns whether and how building can be done. Excessive fire protection regulations, unfeasible parking space requirements (or for a 6-family house in the prohibitively expensive underground garage), 5-6 years until a development plan is actually in place (and by that time construction costs have increased so that the project is no longer viable), 197 expert opinions from all kinds of authorities, etc.
Of course, these points also increase costs. But that is not the main price driver.

And of course, also the availability of land plots. When I see that in metropolitan areas sometimes 60-75% of the purchase price for an apartment is the land value share, it becomes clear why the apartment only has all-in construction costs of €4,000 per sqm but must be sold at €12,500 per sqm.

Interestingly, this is the reason regularly criticized by the construction and real estate industry for the increased construction/purchase/rental costs.

It would also be inappropriate to refer to one's own increased margins ;) One point that comes to mind now that I am in Konstanz today is the many infill development projects. These are not necessarily government regulations, but building a multi-family house in a small gap in the existing buildings naturally makes construction site logistics, etc. significantly more difficult than in a new development area with plenty of space. And in such gaps, there are often some regulations to fit the building into the surroundings. Infill development then usually no longer allows for many above-ground parking spaces, so an underground parking garage becomes necessary. And building underground has become quite expensive in recent years, as we know from the basement discussions.

However, interestingly enough, this is the reason regularly criticized by the construction and real estate industry for the increased construction/purchase/rental costs. But I have never believed that either.

As mentioned, this does not apply to single-family houses.

One example:
In my neighborhood, 4-story apartment buildings are supposed to be built, and this has been dragging on for over 10 years. Currently, new plans are on display and residents have organized themselves to file objections. Such things drive costs up immensely.