Berlin just approved a five year "rent freeze" on apartments in the German capital. The rent caps will be implemented on January 1, 2020, but will apply retroactively to all rental agreements from June 18, 2019 onward (which is when the decision was made). It is estimated that this new law will apply to some 1.5 million apartments.

The move is in response to rapidly rising apartment rents, which grew about 12% in 2017 alone. So I can appreciate where this is coming from.

From what I have read, it will not apply to new construction, which is the first thing I checked when I saw the decision. That would have almost certainly choked off any new apartment construction in the city. With a capped top line, it wouldn't take long for costs to increase and make new rental construction infeasible.

That said, a similar squeeze is liable to happen for existing buildings. It is one thing to cap rents (revenue), but what about utility, maintenance, labor, and other operating costs (expenses)? As costs rise and operating margins tighten, it can become exceedingly difficult to reinvest in, or even maintain, an apartment building.

For more on the announcement, here's an article from FT.