The subject of this article is the differentiation of the rules that govern joint owners’ obligation to bear maintenance costs for a jointly owned property. I examine this issue in the light of the wording and axiology of the Polish Ownership of Premises Act (Ustawa o własności lokali). My starting point is the provision which says that joint owners bear the costs of maintaining a jointly owned property in proportion to their share in the ownership. Next I describe two issues that concern the aforementioned provision which often crop up in practice and are controversial. The first is the admissibility of the resolution that determines different amounts due in advance payments from different owners on the grounds of the category of the premises or parts (e.g. a basement or an attic) each of them holds. The second concerns the admissibility of a co-owner formulating a request for such a resolution. I answer these questions on the grounds of the aforementioned provision and present the legal consequences of a practice which is in breach of this regulation. I go on to comment on the axiological grounds for the differentiation or non-differentiation in advance payments due from respective co-owners. I conclude by giving my opinion on the question whether the provision should reflect the practice and consequently should be amended, or alternatively whether the practice should be corrected in accordance with the existing provision.