(1) The demand for a rent increase under section 558 is be declared and justified to the lessee in text form.
(2) In justification, reference may be made in particular to
1. a list of representative rents (sections 558c and 558d),
2. information from a rent database (section 558e),
3. an opinion, provided with supporting grounds, by an officially appointed and sworn expert,
4. examples of the corresponding rent for individual comparable dwellings; in this context, it is sufficient to name three dwellings.
(3) If an expert list of representative rents (section 558d (1)) that complies with the stipulations of section 558d (2) contains information for the dwelling, then the lessor is to communicate this information in their demand for a rent increase even if they are basing their demand for a rent increase on some other means of justification under subsection (2).
(4) In making reference to a list of representative rents setting out ranges, it is sufficient if the rent demanded lies within the range. If, at the time at which the lessor makes their declaration, no list of representative rents is available that complies with sections 558c (3) or 558d (2), then another list of representative rents, in particular an outdated one, or a list of representative rents from a comparable municipality may be used.
(5) A deviating agreement to the disadvantage of the lessee is ineffective.