Requirements for ancillary apartment, wiring, meters, etc.

According to the attachment, this is only required from 3 residential units in RP. You can see that a lot is country-specific. You did not mention your country. You only have to provide 6 sqm of storage space ;) They are probably more expensive than the modest water meters, which are almost just under a hundred :D

Yes, I mentioned RLP. It’s not just about the meters for me, but also about separate piping. That adds up a bit ‍

It really adds up a bit then ‍

Yes, that’s the reason why some people are so stupid and don’t build a granny flat. It is what it is: if you can’t afford something, you shouldn’t buy it. We can count ourselves lucky that we even have the possibility of construction financing. Ownership on credit. It’s a good thing. The 0.0% financing for the kitchen also fits well into the budget. If necessary, the mother-in-law will be moved to the basement, if it has to be. That’s all okay!!!
But not wanting to lay any pipes for her… I’m back to my “Man, man, man…” most builders around here right now really should be checked for mental maturity: build your house! But don’t build what you can’t afford (not even with the crap).

most builders here at the moment should really be checked for mental maturity

Unfortunately, you are once again completely off in your tone. You judge facts that were not even given, without helping the OP in the slightest. No, probably even providing false information with the reasoning "that's just how it is, I just know." Then better not write anything at all.

Yes, that is the reason why some people are so stupid and don’t build a granny flat. It is simply how it is: what you cannot afford, you should not buy. We can count ourselves lucky that we even have the possibility of construction financing. Ownership on credit. It’s a good thing. The 0.0%_-financing of the kitchen also fits well into the budget. If necessary, the mother-in-law will be moved to the basement too, if it has to be. That’s all okay!!!
But not wanting to lay pipes for her… I’m back at my “Man, man, man…” most builders here at the moment should really be tested for mental maturity: build your house! But don’t build what you cannot (not even with the subsidy) afford.

Now slowly. I thought one could exchange ideas here on a high level, but obviously this forum here, like so many Internet forums, is just a breeding ground for know-it-alls, rude people and dissatisfied complainers who enjoy spoiling things for others.

You have no idea about our financial and family circumstances. What you write is presumptuous and cheeky. My mother is cared for by us. We WANT to have her with us. That was planned long before we heard about the subsidy.

We just haven’t yet been explained the advantage of separate meters and pipes. Hence the legitimate question whether it is necessary.

Apparently you are all-knowing. Congratulations!! We are not and are simply looking for help.

Now pat yourself on the shoulder and tell yourself what a great guy you are. Good luck going forward, but that goes without saying with you.

My mother is cared for by us. We WANT to have her with us. That was planned long before we learned about the grant.

I also said that it is completely OK if you take in your mom. Then just do it. Everything is possible: a third child's room for her, or an additional bedroom… but a room is simply not an option to make a granny flat out of it.
Installing wiring does not cost a fortune. As already said: other costs are what make a granny flat expensive.

It is completely legitimate and legal to meet the requirements for a government subsidy as minimally as possible. Anything else would only increase the misallocation caused by such a subsidy through even more wasted resources.

If the kfw says that an accessory apartment brings a lot of extra money, then it is a good right to include such an accessory apartment (not just on paper).