Change of use of a barn to an apartment in the outdoor area

Hello,

I have a question about building law.
At the beginning of the year, we submitted an application for a building permit for the change of use of a barn to an apartment in the outer area.
At the beginning of May, the application was approved.

In our construction drawing (which was submitted with the building permit application), created by an acquaintance, the walls of the barn were drawn as solid.
However, the actual current state of the barn is timber frame construction, simply clad with boards.

To build a new load-bearing strip foundation and also solid exterior walls (monolithic 36.5 cm aerated concrete), the barn would actually have to be demolished and rebuilt.

Would a complete demolition of the barn be permissible?

If this is not possible under building law, does anyone perhaps have a tip on how the construction project could still be realized?
Maybe within the barn excavate the existing rubble stone foundation, install a new strip foundation/reinforced concrete slab, rebuild 17.5 cm aerated concrete walls, then remove the timber frame construction and install ETICS?

I hope I was able to explain what I mean.
I did not want to ask the municipality directly, as I wanted to first inform myself about my options with you.

Thank you very much in advance.

Best regards

Question for understanding. What did you get approved? A change of use while maintaining the existing new building or a demolition and a new construction? With the answer, you already have the answer to your question about what you are allowed to do.

The construction measure in the application is specified by us as follows. Area: outdoor area Construction measure: change of use of a barn to an apartment Type of construction project: change of use Previous use: barn Intended use: partially apartment

We were given the requirement to continue using one half of the barn as a barn. We have implemented this to the extent that we have made one half garages/storage areas/barn. The other half was then drawn as an apartment. Unfortunately, in the construction drawing for the building permit, the walls were drawn as solid, which they are not in reality. Therefore, the authority probably assumes that we want to keep the non-existent solid walls as exterior walls and only wanted to renew interior walls and insulation. However, this is not possible because, as already mentioned, the barn consists only of wooden stud beams with boards in front. Thus, we may have the problem that if we demolish the barn to implement the building exactly as it is drawn and approved in the construction drawing, we might possibly get into trouble with the authority about why we demolished the barn.

Yep, change of use and no demolition permit or new building permit. Question answered.

Next problem to solve: How to convert the barn with timber frame beams into an apartment. Either find a suitable architect or try to obtain a real building permit.

In our construction drawing (which was submitted with the building permit application), created by an acquaintance, the walls of the barn were drawn as solid. However, the actual current condition of the barn is timber frame construction, simply clad with boards.

Sounds like a clear case of deliberate deception of the authority. But even if the content of the permit is worthless, you now have an orange dot (or is that only available in NRW?) that you can display prominently at the construction site.

If that is not possible under building regulations, perhaps someone has a tip on how the construction project could still be realized?

Judging by your nickname, you have already chosen the dark side of the force. What do you care about lawfulness anymore? Your acquaintance, as the authorized construction submitter, must be familiar with the legal situation and has apparently chosen this route due to the lack of approval possibility. Let him pull the cart out of the mud.

from my side it was definitely not intentional deception.
What I have to admit is that I did not sufficiently deal with the topic of a change of use in the outdoor area and simply did not know that you are not allowed to demolish in order to build a new building on exactly the location of the old building according to the approved specifications of the building authority.
I'm just a layperson and had relied on the fact that it would be fine.
I don't know what the orange dot is supposed to mean? Construction stop maybe? Exactly that is what I want to prevent, and I asked if someone here can help me so that I can find a solution together with the building authority before I start building.