Frank-Peters/Depositphotos.com
Berlin, Germany
When REFIRE reported on Berlin's proposed rent register two months ago, the central question was whether it would survive long enough to become law. On 3 July, that question was answered. The Berlin House of Representatives passed the Housing Security Act, incorporating the Mietenkataster into enacted legislation and making Berlin the first German state to introduce a comprehensive, mandatory register covering its entire rental housing stock. The CDU and SPD voted in favour; the Greens and Left abstained, calling for more far-reaching measures; the AfD voted against, arguing the register would not identify the bad actors it targets. The debate has therefore moved on, from principle to implementation.
The constitutional questions remain, and legal challenges now appear all but inevitable. But for landlords and investors, the immediate issue is no longer whether the register should exist. It is what compliance now requires, and how Berlin intends to use the information it collects.
The significance of the register lies less in the database itself than in the way it changes rent enforcement. Until now, Berlin has relied largely on tenants identifying excessive rents and bringing complaints to the authorities. Under the new system, landlords must proactively disclose tenancy information, while the state itself identifies potential breaches through automated screening. In effect, rent regulation shifts from a complaint-driven process to continuous regulatory monitoring. For professional landlords, Berlin is no longer simply regulating rents; it is regulating information.
That represents a significant change in the relationship between landlords and the authorities. Rather than responding to individual allegations, Berlin is creating the data infrastructure needed to examine its rental market systematically. For professional landlords, compliance becomes an operational obligation rather than a reactive legal issue.
From complaints to continuous monitoring
The law creates a central digital database maintained by the Senate Department for Urban Development and Housing. Once the register becomes operational — the Senate has up to one year to build it — landlords and sub-landlords will have a further twelve months to submit their information. Any subsequent changes, including rent adjustments, must be reported within one month.
The reporting requirements are extensive. Landlords must provide the property's address, floor area, room layout and fittings as defined under the Living Space Ordinance, together with landlord details, household size, any housing eligibility certificate, tenancy start date and duration, net rent, a full breakdown of gross rent including service charges, modernisation levies and the proportionate share of property tax attributable to the dwelling. The system therefore captures considerably more than rent alone, creating a detailed operational database of Berlin's residential market.
Once submitted, the information will undergo an AI-supported preliminary review. The system will automatically identify indications of possible breaches, particularly rents exceeding the local comparative benchmark by more than 20% — the threshold for an administrative offence under the Economic Offences Act — or by more than 50%, where criminal proceedings may follow. Landlords identified by the system will receive notification, while the relevant authorities, ranging from Citizens' Services offices to the public prosecutor, will receive reports for further investigation.
Non-compliance carries meaningful financial consequences. Failure to register, late registration or the submission of incorrect information carries fines of up to €10,000. Where breaches are repeated, involve numerous properties or materially impede enforcement, penalties can rise to €100,000. And the legislation contains a provision that removes any temptation to treat the fine as a manageable business cost: the law explicitly requires that the penalty must exceed any financial benefit obtained through non-compliance. In principle, there should be no financial incentive to withhold information deliberately.
Berlin already has evidence that enforcement works. Since the Rent Review Board began operating in March 2025, more than 93% of cases examined have resulted in findings of excessive rents. In October 2025, the board imposed its first substantial penalty: almost €50,000 against a landlord in Friedrichshain-Kreuzberg whose 38-square-metre apartment was rented at around 190% above the local benchmark. The rent register is not simply applying that enforcement at greater scale — it is changing the model entirely. For the first time, the state does not need a complaint to start looking. It will have the data to identify potential breaches itself.
The practical consequence was neatly summarised by SPD legal expert Sebastian Schlüsselburg. Under the previous system, tenants first had to recognise an excessive rent, assemble evidence and file a complaint. Under the new register, "tenants no longer have to do anything." Schlüsselburg said he expected many landlords to reduce excessive rents voluntarily before making their submissions, precisely to avoid automatic scrutiny.
Alongside the register, Berlin has also launched an online reporting portal allowing tenants to report excessive rents directly while the database itself is still being built.
The legal ground is still contested
The legislation has not ended the legal debate. Landlords' association Haus & Grund continues to question both the necessity and legality of the register. The Berlin Tenants' Association broadly supports the measure but has identified shortcomings of its own, arguing that vacant dwellings remain outside the system and that a non-public database inevitably creates opportunities for inaccurate reporting.
The constitutional concerns raised while the legislation was still in draft have not disappeared. As REFIRE reported in Issue 256 (see article), Olaf Schmechel of lawyers GSK Stockmann argued that mandatory disclosure creates a potential conflict with the constitutional protection against self-incrimination, since information landlords are legally obliged to provide may subsequently form the basis of criminal proceedings. Berlin's experience with the Mietendeckel, ultimately struck down by the Federal Constitutional Court in 2021, serves as a reminder that housing legislation may remain fully operative for years before its constitutional validity is finally determined.
A second, less obvious issue concerns the register's potential impact on the Mietspiegel itself. A database covering almost every tenancy in Berlin would ultimately be far more comprehensive than today's rent index. Should that information eventually influence calculation of the local comparative rent, some observers argue that the result could be higher benchmark rents in parts of the city, producing upward adjustments that run directly counter to the legislation's political objectives.
Data protection presents another unresolved question. While the law relies on Article 6(1)(c) GDPR as its legal basis, the proportionality of collecting personal information on landlords and tenants at this scale has yet to be tested before the courts.
Compliance first, litigation later
Politically, the legislation forms part of Berlin's broader shift towards more active regulation of its housing market. But for institutional investors, the immediate implications are considerably more practical than political.
The register is no longer a legislative proposal but a compliance obligation. Property managers will need systems capable of collecting, maintaining and updating the required information within the statutory deadlines. Reporting obligations become part of routine asset management, while legal advisers will inevitably be examining how the disclosure requirements interact with constitutional protections.
Whether the register ultimately survives judicial scrutiny remains uncertain. What is already clear is that Berlin has fundamentally changed how it intends to regulate its rental market. Rather than relying on tenants to identify excessive rents, it is building the data infrastructure to identify them proactively. Other German states are likely to watch closely — not simply to see whether Berlin's register survives the courts, but whether this new model of data-driven enforcement proves effective.