Expand the monument-protected pavilion in the outdoor area

No. According to §42 (3) Landesbauordnung BW, you will have to appoint a construction manager who must then coordinate all trades. If you have each trade carried out by a different company, the architect is of course a suitable choice for this.

Ah, thanks for the info! Do you have any experience with how it would be if the window was done by Company A, and the rest by Company B? I guess that is probably at the discretion of the city...

Many thanks to you as well for the clear explanations regarding the building application!!

P.S.: In my opinion, the focus of your posts is too much on finances. Your project is more for the love of it than for making money. Keep in mind that an unmotivated (because underpaid) master bricklayer can ruin both.

A listed pavilion... in my opinion, the whole effort is not worth it. Insulating walls, insulating the slab, insulating the roof. The thing also has windows. Then hot water, toilets, wastewater, etc.... this is a passion project.

You are addressing a crucial point here! Yes, it is a passion project. And yes, everything is not as simple as with a "conventional" house. But I wonder if that excludes it being an investment. Because after about 12 years the project pays for itself and generates money. Or what exactly is your objection regarding the "passion project"?

The question is of course whether 75K is really enough... I have a cost estimate for the interior fit-out over 50K, and I do not assume the architect will cost more than 25,000, or what do you think? (but it is probably hard to say from a distance..)

Maybe you can provide us with a few more pictures of the property, then it will be a bit more lively.

But before you put in any further effort, I would make an appointment at the building authority, present the whole thing, and get a first assessment.
In my opinion, the whole thing is most likely not approvable.
Outdoor area and garden house, those are not good keywords.

The insulation will also be a very serious problem.
Being a listed building definitely means that exterior insulation is out of the question.
Interior insulation is elaborate, expensive, inefficient, and also takes away the already very limited space.

The only thing I have no doubt about is that you can rent out the property well.
I come from the area and know what’s going on here with property and rental prices.
There are enough students with wealthy parents who will want to grant the precious little treasures some privacy, peace, and a bit of garden.

Or what exactly is your objection regarding the "LIebhaberprojekt"

You shouldn't go into debt for a hobby project. Because that way you turn what is supposed to be fun into an annoying serious matter.

It would be like buying a vintage Porsche on credit, wanting to drive it to work every day, and then being upset that something is constantly breaking and it often needs repairs and maintenance.

Do you have any experience with that

Not in BW. The qualification of the site manager and proof thereof are not further explained in the law. Neither in BW nor in NRW. Here, the limits of acceptance are quite broad. Even a draftsman is not asked to prove his fieldwork hours.

so if you were to have the window made by company A, and the whole rest by company B?

... then a person from B could take on the site management, so there probably won’t be any problems with the authorities. Whether this person is suitable to create a project to love, within a tightly set financial framework, which must comply with all current standards and also the requirements of monument protection, you ultimately have to judge. Such a master craftsman from construction can be quite robust and, as you can see from the reactions to your picture, may fail to recognize the cultural value of your little gem. The result is cost-effective practical solutions that deliberately disregard the regulations, which in turn leads to trouble, delays, and additional costs.

But I wonder if that excludes an investment.

No, not at all. I think it’s good that you are looking for a meaningful use. I just note that this is not a standard project and any deviation from the standard causes significant additional costs and you already want to save the 5k (fantasy value, I don’t know the HOAI regarding this) for site supervision.

I have already spoken with them, the feedback is initially quite positive

If you have also spoken with the monument authority and no resistance was signaled or their conditions are acceptable to you, that would be enough for me to commission an architect. Arrange another appointment with the monument protectors with them, bring a site plan and photos, and prepare a detailed meeting protocol. Possibly ask for a short written statement that, from their point of view, the change of use is welcomed under the discussed conditions, and then submit the building application.

A master craftsman from the construction sector can sometimes be quite robust and, as you can tell from the reactions to your picture, may fail to recognize the cultural value of your little gem. The result are cost-effective practical solutions under deliberate disregard of the requirements, which in turn leads to trouble, delays, and additional costs.

That sounds like a good hint. Wouldn't the master craftsman, if he were to take over the construction management, be interested in complying with the requirements?

I just note that this is not a standard project and that every deviation from the standard causes significant additional costs and you already want to save the 5k (fictional value, I do not know the HOAI in this regard) for construction supervision.

I had previously mentioned 25k, which I included for architect services (out of the total 75k), so I would be willing to pay more than 5k. At the same time, I wonder if that is enough, since I have also received such widely varying cost estimates from the architects.

If you have also spoken to the monument authority and no resistance was signaled or their conditions are acceptable to you, that would be enough for me to commission an architect. Arrange another appointment with the monument protectors with him, bring a site plan and photos, and take a detailed meeting protocol. Possibly ask for a brief written statement that the change of use is welcomed from their perspective under the discussed conditions and submit the building application.

That sounds like a good, feasible way. So far I have only spoken with the building authority... Thanks for that!

Isn’t the master craftsman, insofar as he would take over the construction management, interested in complying with the requirements?

I don’t know. After your posts, my mind starts to run wild (I’m exaggerating): You find a refined architect who presents a thoughtful and loving plan with a detailed construction description considering the special requirements (outdoor area, non-privileged, monument protection, fire protection, thermal insulation) and selection of special building products. Then the rough-handed practitioner comes along, who, because of your financial constraints, has calculated a bargain price with standard materials and put it into the offer. He then says if he has to do it the way the architect planned, it will cost twice as much, which disrupts your amortization calculation. Therefore, he suggests doing it his way, the way he has always done it. And suddenly you’re stuck in a dilemma. OK, that’s pessimism, there are also architects who are incompetent and craftsmen who are brilliant.

would therefore be willing to pay more than 5k

My imagined 5k referred only to construction management. You definitely need an experienced designer because your project must be well justified. I would advise against a university graduate with six months of internship experience. And you have already had contact with architects. Ask them what the building application and construction supervision usually cost. It’s also not a bad idea to have a professional who controls the craftsmen’s work.