Heating for bungalow with 2 residential units

Hello dear forum community,

my wife and I are currently planning a new building together with her parents.
It will be a bungalow with two adjacent residential units (total living area approx. 250 m²).
As laypeople in planning, we are now facing a few questions that challenge us a lot or where we do not know what is ultimately best.

One of these questions is how the heating should be designed:
So far, it is planned to be a heat pump with geothermal drilling.
The central question is:
A shared heating system for both residential units or a separate one for each?

Several people have advised us to have a heating system for both residential units, others advise against it and say we should definitely separate them.

Therefore, we are very interested in your opinions and especially your experiences.

We currently have no idea how big the price difference is between the two options.
In addition, the continued use of her parents' residential unit is important to us.
Since we (still) have no children, we would like to be able to rent out the unit later if necessary.
At the latest then, we must be able to clearly separate the consumption without having to do a major conversion...

Thank you very much in advance for your opinions and your input :)

The most important thing first: Do you want to build a semi-detached house with real division of the plots or without real division in a homeowners' association (WEG) in a semi-detached house with 2 apartments living with the parents? I would strongly advise a real division of the plots, as the resale value is significantly higher and a semi-detached house as a WEG can hardly be marketed. If you only had one heating system for both houses, you would automatically have the WEG, because a real division is not possible this way (with a shared utility room in the house). Therefore my recommendation. You must build two separate heating systems and utility rooms and carry out a real division as a semi-detached house, otherwise you would really have an almost unsellable house with 2 apartments, unless it is in the greater Munich/Berlin/Hamburg/Frankfurt area, etc. Build the heating systems separately! Otherwise you will have a WEG with 2 owners that may be quarrelsome, where one can only make changes if the other agrees.

And manage the finances separately. In other words, you build a duplex and the parents build the other on the second plot, otherwise this can end as a building community without any contracts in a familial and financial fiasco for you. Sorry for all the warnings, but you simply need to know this. Because building a duplex on one property with 4 owners as a community is more than funny. And what if both parents eventually pass away? Then you could suddenly have almost nothing. Because your wife would then be registered with 3/4 in the land register and you only with 1/4. Then in case of a divorce you would have to pay out 75% right away. With separate houses, you each have a 50% share in the property and the parents’ house can also still be easily sold in case of a divorce.

The most important thing first: Do you want to build a semi-detached house with real division of the plots or without real division in a condominium community (WEG) in a semi-detached house with 2 apartments living with the parents? I would strongly recommend a real division of the plots, as the resale value is significantly higher and you can hardly market a semi-detached house as a WEG. If you only had one heating system for both houses, you would automatically have the WEG, because a real division is not possible that way (with a shared utility room in the house). Therefore, my recommendation. Build strictly two separate heating systems and utility rooms and carry out a real division as a semi-detached house, because otherwise you would really have an almost non-transferable house with 2 apartments, unless it is in the greater Munich/Berlin/Hamburg/Frankfurt area, etc. Build the heating systems separately! Otherwise, you end up in an unfortunately quarrelsome WEG with 2 owners, where one can only change something if the other also agrees.

Thank you very much for your answer. Currently, the plan is to carry out the project without real division of the plots. So accordingly as a WEG. Whether it would be feasible with a real division would have to be checked again if necessary.

Special funds of an owners' association can also be sold easily. The problem with this construct is that you might encounter legal frameworks that are more aimed at an apartment building with 30 units than at a duplex.

If you stay with the WEG, I would tend to go for a heating system with billing based on a heat meter. Geothermal energy has fairly high fixed costs and is generally not worthwhile for a single dwelling unit and current new building standards. With two units, you come much closer to making it worthwhile. A problematic question could be where the heating room is located and how both have access to it. As mentioned, the topic of owners' associations is actually aimed at multifamily houses.

In terms of price, you are certainly cheaper with a heating system for two units. A heat pump (whether air or geothermal) is not twice as expensive for double the output.

Please quickly insert the completed #questionnaire and get continuous help.

Laypersons should seek advice, either in a forum or from professionals. But do not try to cast your nets through a patchwork of individual question threads after gaining bits of knowledge here and there (or even piece together your house from that, which in threads A to Z has become the winning variant in voting by other laypersons). There are some experienced contributors here. And I myself am a nationally active building consultant, by far not the only one of this kind (others maybe only regional, but there are pretty much always some), and as a fallback (or king’s way) there are also the classic architects listed in all business directories.

You already have several heating circuits in one residential unit, possibly with individual room control. Measuring meters for consumption can also be integrated at several points in a network. I do not see 250 total square meters to be heated as a compelling reason for a second heat generation unit under any circumstances. Only with a controlled residential ventilation and its heat recovery would you have to think twice. Only here is separation mandatory, regardless of ownership or whether there are kinship relations with the other party.