An available room could reduce living costs or provide a transition for someone you know. But that should not immediately become a finished offer. First you must clarify whether you can enable the specific use legally and contractually and how it should work in practice. Calling it a flatshare (Wohngemeinschaft) alone does not answer the contractual framework nor responsibility for payments and keys.
Establish your own role
Have your full tenancy agreement including amendments ready. Clarify who is a party to it and which provisions about transferring living space are contained in it. If several people are main tenants, the preparations must not rest solely on the decision of one person. If anything is unclear, ask what consent or further agreement is necessary in the specific case.
This article deals with planning a longer-term partial subletting. Tourist short-term rentals, charitable or specially bound forms of housing can trigger additional rules. Information about ordinary subletting is therefore not proof that an advertisement for changing holiday guests would be permissible. Keep the actually planned use in mind.
Check the scope of application before drawing conclusions
§ 11 MRG limits, in its area of application, the reliance on contractual prohibitions of subletting and names important reasons against a subletting. These include, for example, full transfer, a disproportionate consideration or certain issues of occupancy and communal life. This provision is not a general permission for every flat and every contractual constellation. [MRG11]
Therefore first have it clarified whether and to what extent the relevant rule applies to your tenancy. Avoid the oversimplified conclusion that a single further room still used by you secures any other transfer. For a professional classification actual use, contract content and the concrete form of living must fit together. Advice should therefore know your documents and your planned procedure.
What is actually to be shared?
Our editorial recommendation: Describe the proposed room and the areas to be used jointly so that both sides expect the same everyday life. This includes the kitchen, bathroom, storage options and, if applicable, access to ancillary areas. A room sketch can be helpful for coordination. However, it does not turn unresolved building law or contractual questions into already confirmed rights.
Discuss typical everyday points openly: working hours, visits, quiet times and communal cleaning. Formulate realistic arrangements instead of a long list of hardly enforceable rules. If costs are shared, it should be clear what amount is intended for what. A round monthly sum does not yet explain how later additional payments or changed expenses will be handled.
Do not mix main tenancy agreement and sublet agreement
Record different payment obligations and contact channels separately. Your obligation towards your landlord is not changed merely because another person transfers an amount to you. Which agreement between you and the other person is legally appropriate belongs in a suitable contract review. A freely copied internet template can overlook important conditions of your original contract.
Example, purely fictitious: A tenant wants to hand over a room for a year, but her own contract may end earlier. Before making a commitment she therefore clarifies the actual term of her tenancy and the consequences for the planned use. She does not promise a period that she herself cannot reliably offer yet. An expected contract extension remains marked as an expectation.
Document the handover in a manageable way
When the legal and contractual prerequisites are clarified, a factual condition and key documentation helps. Separate private items from shared equipment and record known defects. For communications and repair reports it should be clear who receives which message and who acts vis-à-vis the original landlord.
Also plan the end of the use: return, outstanding accounts and personal belongings must be later assignable. This organisational preparation is not a statement about permissible notice periods or deposit conditions. Such questions must be examined for the concrete agreement. A well planned shared everyday life begins with neither side promising greater security than has actually been clarified.