(1) Costs assumed by the lessee or assumed by a third party for the lessee or covered by subsidies from public authorities do not form part of the costs spent within the meaning of section 559.
(2) If the costs of the modernisation measures are covered in full or in part by low-interest or interest-free loans from public authorities, then the amount of the increase under section 559 is reduced by the annual amount of the interest reduction. The latter is obtained by computing the difference between the reduced rate of interest and the going market interest rate for the original amount of the loan. The going market interest rate for first-priority mortgages at the date when the modernisation measures ended is the relevant interest rate. If subsidies or loans are used to cover ongoing expenses, then the amount of the increase is reduced by the annual amount of the subsidy or loan.
(3) A lessee loan, an advance rent payment or a service performed for the lessee by a third party for the modernisation measures are equivalent to a loan from public authorities. Funds from the financial institutions of the Federal Government or of a Land are deemed to be funds from public authorities.
(4) If it cannot be ascertained in what amount subsidies or loans have been granted for the individual dwellings, then they are to be apportioned according to the ratio of costs spent on individual dwellings.
(5) A deviating agreement to the disadvantage of the lessee is ineffective.