Flat roof without slope okay? Water will then stand on it, right?

Hello,
for our extension (timber frame construction), a flat roof with tapered insulation was planned. The architect later decided not to install the tapered insulation. Now the roof is finished and constructed as a "zero-degree roof." After rain, water stands extensively about 2 cm deep in the middle, although overflows are provided on two sides at the roof edge. The water eventually evaporates, causing typical dirt marks, which is unsightly since you can see it clearly from the upper floor.
The architect says everything is fine with the roof, a zero-degree roof is permitted, and it is not problematic that water remains standing on it.
I am now just wondering, since it is also a timber construction, how long such a roof will last or if this design is even inadmissible?

Flat roofs with zero slope are permitted, provided they are designed for it (K1/K2).

I am just wondering, since it is also a timber construction, how long such a roof lasts or if this type of construction is even not permitted?

The question is absolutely justified, as the combination of flat roof with wood usually also means insulation with fiber/wool. In case of water ingress, this is the worst-case scenario.

Is the question why the roof is being constructed differently than was apparently agreed before? If you google a zero-slope roof, I wouldn’t want something like that...
Found quickly like this...

A zero-slope roof or water roof is a special flat roof construction that is designed without any slope. Such a 0° construction is very prone to damage because a single leak can cause the entire roof layer package to become soaked. Due to the lack of slope, it is exposed to the following additional stresses:

[*]Higher static load due to standing water
[*]Extensive ice formation in winter
[*]Increased deposits of dirt and leaves
[*]Red algae formation in the transitions between wet and dry areas

and it continues:

After numerous problems and damage cases in the past, zero-slope roofs should preferably no longer be built. Due to an existing roof structure, however, in a refurbishment the construction of a zero-slope roof can in individual cases be the only possible option. Then attention must be paid to appropriate sealing. It is better to install a tapered insulation so that the stresses described above do not lead to damage.

For what reason does the architect now think that this is better than a tapered insulation?

Completely right what you found there. 0° above living space and then also wood is so stupid that the architect should be sued for it...

Hello,
for our extension (timber frame construction), a flat roof with sloped insulation was planned. Later, the architect decided not to build the sloped insulation. Now the roof is finished and executed as a "zero-degree roof." After the rain, the water stands widely about 2 cm deep in the middle, although overflows are planned on two sides at the roof edge. The water eventually evaporates, creating typical dirt marks, which is unsightly since the upper floor looks directly at it.
The architect says everything is fine with the roof, a zero-degree roof is permissible, and that water staying on it is not problematic.
I am now just wondering, since it is also a timber construction, how long such a roof will last or whether this execution is even impermissible?

Honestly, I doubt the architect made this decision without your approval. An architect can only make proposals and then present them to you for approval. Only you can decide. If the architect really decided/instructed this unilaterally without your consent or approval, then he is simply "stupid," or you have him by the balls.

Get an expert and have the situation assessed. If you approved it, you will be left with the costs of dismantling/repair. If you didn’t know anything about it, then come to an agreement. If no agreement can be reached, then lawyer.

You know ignorance of the law is no excuse! I know that’s easy to say. You are just the builder/layman believing you hired a professional. But not reacting in such a sensitive matter as flat roofs regarding slope & waterproofing was your mistake.

My plumbing guy wanted to chisel out half of the 36.5 cm outer tile for the ventilation ducts or the adapter of the ducts. I had him keep looking for an alternative until it no longer happened.

We also have a flat roof (wood) on a masonry house. However, our primary goal was to have the appearance of the exposed beam construction (as would be typical for timber framing). We had long discussions with our architect and also with the roofer. With a roof built like yours, I would - to put it mildly - be shitting my pants that nothing would go wrong in the long term.

But let me hear whether the architect decided that alone, or where that actually comes from...

Btw... The roof doesn’t just suddenly come flying in. You can already see what’s happening during construction. Didn’t you have doubts back then?