The size of an apartment is decisive for many things. First and foremost, of course, it ensures that the residents feel comfortable and have enough space for their needs and activities.
... and, of course, it also serves as the basis for calculating rent, utilities, housing subsidies, the proportionate costs of a home office, etc.
There are often significant deviations, which can have a variety of reasons: The apartment was rented for a specific group of users, but this has subsequently changed—the children have left home, the partnership has broken up, age and/or illness are having an impact, income has changed, etc.
The aspects mentioned are subjective—objectively, of course, every apartment has a certain size, which can be found in the lease agreement.
That would be nice!
Many rental agreements make no mention of size whatsoever. Or the tenant trusts that the information in the contract is correct – the landlord trusts that the information he has about the size of the apartment is correct. This information comes from many sources: from the building file, from the sales brochure, from the declaration of division, from the previous owner's documents, from the broker, from the architect, from his own measurements, etc.
Added to this is another problem that makes the matter rather confusing: the various creators of the aforementioned documents may have used different measurement and calculation methods! ... and that would not even be prohibited!
Living space can be calculated according to DIN 277, a method mainly used in planning and construction. Alternatively, the methods of the II. Calculation Ordinance or the Living Space Ordinance can be used. The latter are required by courts if rental agreements either do not provide any information or do not specify the method used.
It can be helpful to take your own measurements and agree on them between tenant and landlord as the basis for the contract. The method to be chosen can be found on the Internet; tenant and landlord associations provide useful information on this. Real estate agents are also helpful as experts.
If a conflict nevertheless arises, a recent ruling by the Federal Court of Justice must be taken into account. (Ref. VIII ZR 234/18 of December 11, 2019.) This ruling states that the tenant is not entitled to a change in the lease if it turns out that the landlord has assumed an inaccurate, i.e., too large, area. (Incidentally, this only applies if the calculated rent is below the local comparative rent.)
The Federal Court of Justice considers the difference between the square footage assumed by the landlord and the tenant to be a "mutual error." Neither party knew how the other party had determined the size of the apartment. Thus, the basis of the lease agreement no longer applies.
Consequently, it is possible to adjust the lease agreement to the new findings, i.e., square meters.
So if you feel that the actual size of the apartment may differ from the information in the lease agreement, you should simply measure it using the above-mentioned sources and compare the result with the other party to the agreement.
This can help avoid a potential conflict.
