Modernisierungsumlage (§559 BGB): 8%, and the Caps That Bite

After a Modernisierungsmaßnahme you may raise the annual rent by 8% of the costs attributable to that flat (§559 BGB). It is a permanent increase and needs no tenant consent – but it is hedged.

Modernisierung vs. Erhaltung. Only the measures listed in §555b count: saving energy or non-renewable primary energy, water saving, a lasting increase in Gebrauchswert (utility value), a lasting improvement in general living conditions, or new living space. Erhaltung – repairing or replacing something worn out – is your cost. Replacing a 30-year-old boiler is mostly maintenance dressed as improvement, and §559(2) obliges you to estimate and deduct that Erhaltungsanteil. Grants and cheap public loans come off too (§559a).

The caps (§559(3a)). Within six years the monthly rent may rise by at most €3 per m² – or €2 per m² if the rent before the increase was under €7 per m². For a heating installation qualifying under §555b Nr. 1/1a, the heating portion is capped at €0.50 per m² over six years.

§559e BGB allows 10% instead of 8% for a qualifying heating replacement where public funding is actually received. Caution: §559e was drafted around the 65% renewables rule of the old GEG, which the GModG repealed in July 2026. How it now reads in practice is worth checking with a lawyer before you rely on it.

Procedure.

• §555c: announce in Textform at least three months before works start – nature and scope, expected start and duration, expected rent increase and expected future Betriebskosten; point out the hardship objection.
• §555d(3): the tenant has until the end of the following month to raise a Härteeinwand in Textform.
• §559b: declare the increase in Textform with a full calculation. It is owed from the third month after receipt – pushed out by six months if you never announced properly, or if the actual increase exceeds the announced one by more than 10%.

As a single flat owner in a WEG, the community usually decides the works; you pass on your share.