(1) The rent increase under section 559 is to be declared to the lessee in text form. The declaration is only effective if the increase is calculated in it on the basis of the costs incurred and if an explanation is provided in accordance with the prerequisites set out in sections 559 and 559a. Section 555c (3) applies accordingly.
(2) The lessee owes the increased rent from the beginning of the third month following receipt of the declaration. The period is extended by six months
1. if the lessor has failed to notify the lessee of the modernisation measure as required in accordance with the provisions of section 555c subsections (1) and (3) to (5), or
2. if the de facto rent increase is higher by more than 10 per cent than the increase notified.
(3) A deviating agreement to the disadvantage of the lessee is ineffective.