In Berlin basically all units are regulated (can't increase rent beyond inflation once you sign a contract, all contracts are indefinite by default and usually only breakable by the tenant, and only newly built units or such that have been renovated at a cost of more than a third of their entire value can be rented to new tenants at more than 10% above average current renting price for a comparable unit in the same neighborhood/comparable location).
The result is that while purchase prices (which are unregulated) have continued to increase in line with the rate of increase in other desirable world cities, rent prices are increasing at a much lower rate - and they started relatively (compared to purchase price) low to begin with.
Of course it's not a perfect system and i wish they'd cut down on the burocracy to enable building more units faster, but it did show an effect.
The result is that while purchase prices (which are unregulated) have continued to increase in line with the rate of increase in other desirable world cities, rent prices are increasing at a much lower rate - and they started relatively (compared to purchase price) low to begin with.
Of course it's not a perfect system and i wish they'd cut down on the burocracy to enable building more units faster, but it did show an effect.