Are phases 1-4 sufficient? Or additionally 5?

When I think alone about the drawing of the ridge etc. connection points from your [Traufhöhenthread], I strongly advise against the idea of letting the shell builder mess around based on submission plans. After all, we are talking about a multi-family house.

I haven't built an entire house, but only dormer windows according to service phases 1-4, and there were definitely missing detailed plans even for this small project. Without plans, the craftsmen always carry out their trade as simply as possible. It's unfortunate for the subsequent trades, as they are not taken into account at all. As a layperson, you always see in hindsight where better planning would have been necessary. But by then facts had already been created. I definitely missed the detailed plans on how to better integrate the roller shutter boxes so that no ugly surface-mounted boxes would be necessary. I think we found a solution, but it would have been much better and less stressful with service phase 5.

A standard house completely contracted to a general contractor usually does not necessarily require a service phase 5, as they do it themselves. Individual trade contracts (here e.g. [Rohbauer]) require a service phase 5, not only for the object planning (architect) but also for structural planning (engineer).

Without plans, the craftsmen always carry out their trade as simply as possible.

I would put it differently: for craftsmen, "no plan" or "a non-specification of a detail in a plan" is not simply "no instruction," but an instruction with the content "let your routine run free." The problem is: jazz musicians can improvise, but symphony musicians absolutely need a sheet of music (and a conductor, which is why a site manager who is not only on paper is so important!).

We are currently facing exactly the same decision. What Lumpi writes - phase 5 not necessary for general contractor - is also stated in Wikipedia: One of the general contractors said exactly that as well, save the money and only commission up to the approval; he doesn't need it. In a simple single-family house, these are all standard anyway; Ytong here, gypsum boards there...

However, we do wonder how sensible it is to buy an individual approval plan expensively from the architect and trust that the general contractor implements it as intended.

Phase 5 accounts for 25% according to HOAI and is quite a significant cost. Perhaps it could then be produced more cheaply afterwards by a younger colleague - in case the general contractor is still missing something?

One of the GCs said [...] he doesn't need that.

I read that as an honest statement meaning: "my people wouldn't look into such plans anyway, they always follow the same old routine." This also implies ...

- in case the GC is still missing something?

... that the GC will not report back if, from your point of view, something is missing – because in his opinion it can be improvised and solved without coordination.

However, we do wonder how sensible it is to buy an individual approval plan expensively from the architect and then trust that the GC will implement it as intended. [...] Maybe it could then be made more cheaply afterwards by a younger colleague.

I would quite certainly deny the trust in an implementation as expected here. From my point of view, an execution plan is much better done by the person who also developed the design. But in principle, you can also hire a "younger colleague" for this. I would strongly advise not only having him make drawings here but also entrusting him with construction management. If you just have plans made that the GC’s piecework bunglers do not look at, that would be money thrown away (which you would probably be better off spending on the complaining lawyer). Get both an execution planner-and-construction manager as well as an accompanying expert (how many times he needs to be involved depends on the complexity: once more for each bay window and roof area than for the run-of-the-mill).