Additional costs for residential units

Hello,

I am currently planning a new building (my first), which is to be equipped with 2-3 residential units and will probably be implemented with an energy efficiency of 40+. Basically, it could be called a multi-generational house. Initially, only 2 residential units (one on the ground floor, one on the upper floor) are to be built out, but in the long term, a third residential unit (attic) is also to be created. I would initially like to leave the attic in shell construction but have all the connections, lines, etc., laid. So no further structural measures should be necessary afterwards to be able to use it as a separate residential unit.

As far as I am informed, the following requirements apply for a separate residential unit:
- Own, lockable entrance
- Own electricity meter
- One kitchen connection each
- One bathroom connection each (toilet and shower)
I hope I haven’t forgotten anything here. If so, please let me know.

Now to my question: To be able to plan a little better, I would like to explore how much an additional residential unit (i.e., laying connections for an additional kitchen and an additional bathroom and setting up a separate electrical circuit with a separate electricity meter in the utility room) costs. In other words, the additional price that should be planned if you turn a regular single-family house into a house with 2 or 3 residential units.
At first, I am only interested in the connections, i.e., the potential for a residential unit (not yet the price that an additional kitchen or sanitary installation would trigger).
I hope you can help me. Many thanks in advance for all comments and explanations!

I hope you can help me. Thanks in advance for all comments and explanations!

Try to find out how the search works here. Keywords: granny flat, KFW. You will see that you come across an FAQ and can repeatedly read that playing landlord with the batch size "one housing unit" is usually a zero-sum game / Hornberger shooting and that the KfW efficiency level 40 as a target is viewed critically / controversially.

Hello,

thanks in advance for your answer! I had indeed already tried searching. I might have overlooked suitable threads, but mostly I only found various posts where other forum members accused others of "megalomania" and "grabbing subsidies." Sorry, that was unfortunately not helpful for my question. My concern here is less about financing clarification (I’m not so worried about the money but of course don’t want to pay more than necessary).

My question is more of a technical-calculative nature: What should be roughly planned to provide connections for a kitchen, bathroom, and a separate electricity meter to an (additional) floor? Are there any other significant costs if one wants to create an additional dwelling unit?
And further questions would be something like: Can these costs be reduced (e.g., by arranging the rooms in question all stacked on top of each other), or are there general tips on how to plan a house with multiple living units to keep costs as low as possible?

The fundamental question ... are 3 residential units in the planned development area permissible on one plot? Considerations also include things like necessary parking spaces for cars, etc.

Only connections should not be so expensive if they are available and only need to be extended to another floor.

A shell construction for the "later expansion" is not eligible for KfW: sanitary installations must be present, just as residential units themselves must generally be completed in order to receive subsidies. Planning with regard to later expansion is not sufficient. It is also not enough to declare a hole in a room or attic with a drain, shower head, and wires with an outlet for a stove as a granny flat. So: do what you want. But do not expect official approval for future planning.

Considerations also include things like necessary parking spaces for cars, etc.

The property will have three parking spaces. However, I was not aware that this is mandatory. Do you have to provide parking spaces in order to declare a residential unit as such?

Are 3 residential units allowed on one property in the planned building area?

This is under clarification. A friend has already pointed out to me that this certainly may not be the case. A related question: Are granny flats evaluated differently than residential units? So for example, would it be more like a main apartment and 2 granny flats instead of 3 equivalent residential units? Has anyone perhaps ever been in such a situation and have experience?

Only the connections should not be that expensive if they exist and only need to be extended to an additional floor.

Can it be specified more precisely what kind of costs we are talking about per residential unit/floor? Is the separate electricity meter, which as far as I have read must also exist for a residential unit, a relevant cost factor? Or is it basically no big deal to install one meter per floor in the utility room?

A shell construction for "later expansion" is not eligible for KfW: sanitary facilities must be present, just as residential units generally must be completed in order to receive subsidies. A plan for later expansion is not enough. It is also not enough to declare a hole in a room or attic with a drain, showerhead and cables with an outlet for a stove as a granny flat.

That is interesting. Is there any official regulation specifying exactly what must be fulfilled for KfW to recognize a residential unit as such? Some years ago, an architect/developer assured me that for KfW the potential of a residential unit alone would suffice because it is basically about creating energy-efficient living space for more people. Of course, all wiring and connections must be present, but by the end of the construction phase the kitchen does not have to be installed or the bathroom furnished. The loan had long been disbursed by that time, so the subsidy was already granted. Or is it then about the repayment bonus which may be refused? The complete attic conversion is not immediately necessary for us due to space constraints, so I would very much like to do that later, but initially create all prerequisites so that I only have to do the interior finishing (tiles, flooring, wallpapering, furnishing) later when the residential unit is occupied.

So: do whatever you want. But don’t expect official approval for future plans.

I’m pretty sure I don’t expect official approval of anything from a forum ;) Don’t worry. What I hope for are some information and a general exchange with more experienced home builders.