Help: Identifying causes of high electricity and water costs

Yes, I explain the gas issue by the lack of insulation.

Was that a consumption-based energy certificate? It is significantly cheaper to produce than a demand certificate. If consumption-based, then it says nothing about the temperature generated with the listed energy amount.

Were the previous residents old? Someone sick? Someone severely underweight? Infant? For such reasons, I see differences in the heating cost billing of up to 2.5 times compared to, for example, male bachelors who often get by with surprisingly little.
I would ask the administrator instead of the realtor. He must be listed on the protocols. These should be looked at anyway.

Best regards Gabriele

Electricity consumption is completely user-dependent, so I wouldn’t pay much attention to it. Old appliances (refrigerator, freezer chest, television, lamps, etc.) consume a lot of electricity. The gas consumption would also deter me more. Of course, this is also very user-dependent. How warm is it heated? It makes a significant difference whether you have 22° or 20° in the place. Ventilation behavior is also relevant. With night/day setback, one can also make many mistakes.

Thank you for the tips, I have now contacted the previous tenant and asked politely. Let's see, I'll keep you posted.

By the way, I would only start insulating the wall at the very end. Before that, energy is lost through the windows, roller shutter boxes, roof. The adjustment screw "walls" is surely the smallest and also one that rarely pays off. The heating pumps in this construction year may not yet be demand-controlled. But we are also talking about maximum savings of maybe 100,- € per pump per year.

Oh, thank you very much! Oh man, then the apartment is probably not an option. There are three parties among the owners and only we would have the entire attic space. The wooden windows would then have to be replaced and they have a special style ([Fachwerkhaus-Stil :-), is that the correct term?]). The owners' association would have to agree to that and we would certainly bear all the costs. As far as I understand, the roof, door, and windows are common property. Is that correct?