Cost estimate for renovation of medical practice 186 sqm

The costs will be somewhere between 30,000 and 200,000 euros, says my crystal ball.
"ggf. etwas Elektro" is not suitable for tendering. It can be 500 € for new switches and a few more sockets done by yourself, or 10,000 euros for a new fuse box and new wiring + sockets by an electrician.

Regarding the planned measures:

Changing only your own apartment to underfloor heating with an oil central heating system is not possible. Well, you can, but you need an extra heating circuit distributor with a mixer.
You also can't simply build up 15 cm - unless you are not taller than 1.70 m. Otherwise, you won't fit through the doors. Unless there are extra high doors, then it just looks crap but you can get through. All in all, a comprehensive underfloor heating system with a 10 cm buildup is rubbish in this case if everything else (screed, doors) is okay.

There are thin-layer systems for underfloor heating to retrofit on existing screed. These have a buildup of 2-4 cm. Costs are around 50-100 €/m depending on the type. But here you again have the oil heating mixer issue, and hydraulically it is difficult if all other apartments have no underfloor heating.

If the old screed is to be removed, the buildup will be different again, but even then, you have the temperature problem and a hydraulic one. You should definitely clarify this with a specialist beforehand. But if money matters: just replace radiators as needed.

If you completely renovate the bathroom and also make the screed new there, you can install underfloor heating in the return line of the towel radiator, then you always have a warm floor in the bathroom. You can then simply make the bathroom floor entirely from Wediplatten, mill slots for the underfloor heating into it, and tile it. Instructions for this are on Wedi’s homepage. Thick insulation, inexpensive, simple.

Why drop the ceilings? You live on the ground floor; upstairs is heated. No heat goes upwards. And it looks nice.

Windows: The window construction year/production date can be found in the glass spacer – the silver strip between the panes. Is there 1986 or 7-86 or 7/86 or 01.07.86 or 86 somewhere? So are the windows from the year the house was built? Does the wooden frame look good and all fittings as well? Then have the glass panes replaced with new ones with thermal insulation glazing. Current panes have a U-value of 3.0; new double glazing have 1.0. Saves 200 kWh/m² of window area per year. New seals on the sash lead edges reduce drafts and save ventilation losses.

Are windows the responsibility of individual owners or WEG / relevant to house money? Clarify beforehand.

If I understand correctly, you are only buying the ground floor. The floors above have different owners. They would have to agree to the change of use first, right? Has this already been clarified?

Are windows the responsibility of individual owners or relevant to the WEG / service charges? Clarify beforehand.

Windows are always common property. However, nothing prevents you from upgrading at your own expense. But you may not change the appearance of the windows without the approval of the WEG.

Also, with the floor structure and changes on the outside, WEG approval is probably required.

Intervention in the central oil heating system as well (i.e., new mixing circuit, etc.).

However, nothing prevents you from upgrading at your own expense.

Sorry, nothing works without the community's consent! You are destroying communal property if you remove a window, please keep that in mind.

Intervention in the central oil heating as well (that is, new mixing circuit, etc.).

Yep, that's right. A proper reading must be possible later on.

Sorry, nothing works without the community's consent! You are destroying communal property if you remove a window, please keep that in mind.

If you replace it with a higher-quality window that does not change the appearance, you can do that. Of course, it then becomes part of the communal property.

If you replace it with a higher quality window that does not change the appearance, you can do it that way. Of course, it then becomes part of the common property.

Sorry to correct again, but your statement is factually incorrect. Windows are ALWAYS common property and you have no legal basis to replace the windows on your own authority. Even if something else is stated in the division declaration, this is not legally binding, as the Condominium Act takes precedence. At most, maintenance can be shifted to the respective owner through the division declaration. Thus: If the owners' association does not agree, you are not allowed to replace the windows. Oh yes, this also applies to the exterior window sills, load-bearing walls, and the apartment entrance door. To my knowledge, even exterior blinds and shutters are included – only the internal pull cords, for example, belong to the separate property.