Can the lessor demand that I pay the rent owed by my flatmate? Can I terminate the lease independently if I decide to leave a flat-sharing community? Am I liable to the lessor for damage caused by my flatmate? Initial issues of contract law often expand to include questions touching on family and corporate law.
A strict distinction must be made between the relationship among the tenants themselves (internal relationship) and that between the lessee and the lessor (external relationship). According to widespread legal doctrine, in their internal relationship tenants usually form a simple partnership which, by sharing common premises and common resources, pursues a common purpose. Special provisions apply in the case of a civil law union (marriage or registered partnership).
To reply to the earlier questions, one should refer to the external relationship. In this case, in whosesoever name the lease was concluded is decisive, whereby for evidentiary purposes the signatures on the lease are generally considered.
In the case of multiple tenants, a co-tenancy agreement exists, otherwise one proceeds on the assumption of a separate sublet agreement. The distinction has wide-reaching implications: Only co-tenants form a simple partnership, giving rise to their joint and several liability and even a prior obligation to dissolve the partnership before the lease can be terminated. In contrast, in the case of a sublet agreement, each party can independently bring about the dissolution of the joint household.
Romantically involved couples – a special case?
In principle, the same applies to couples: a sexual relationship between two persons does not necessarily constitute a simple partnership, and certainly no relationship of relevance under family law. If the partner does not sign the lease, there may be no basis for claims between the lessor and the subtenant.
In contrast, spouses or registered same-sex partners officially enter into a union governed by family law, which, in the absence of the agreement of one of the partners, can be dissolved only after a 2-year waiting period. Because the vital centre of such a partnership, i.e. the family home, is protected by special provisions, even the subtenant is in a quasi-contractual position regarding the termination of the lease.