Renting out a holiday apartment on Airbnb has become a lucrative and fast-growing business model - which the popular online platform is actively encouraging, according to new research by Germany's Süddeutsche Zeitung (SZ) newspaper.

After analyzing a database of over 37,000 Airbnb offers in the ten biggest German cities, the newspaper - working alongside reporters from Belgium's De Tijd, Le Monde in France, and Trouw in the Netherlands - found that there were around 1,290 landlords offering more than one apartment in the country on Airbnb, a development that is driving up rental prices and emptying many inner city neighborhoods.

Some 58 percent of all offers on Airbnb in Germany are entire apartments or even apartment blocks - meaning professional landlords are effectively the core of Airbnb's business. Meanwhile, offers of single beds in shared flats make up less than 2 percent of the site's ads.

Some rental companies, like Cologne-based Homerent Immobilien make a turnover of some 4.5 million euros ($4 million) by using Airbnb as part of their business model. The paper also found that many of these companies disguise their offers with advertising suggesting they are being made by private people renting out their own homes.

There are also start-up companies in Germany that take over the management of your Airbnb property, by posting the ad, providing the keys with guests, and cleaning it afterwards.

Taking apartments off the market

Berlin is experiencing an acute housing shortage

Even though Airbnb told the SZ that the focus of its business model was "home-sharing," the platform appears to actively encourage professionalization - with tips including stipulating set check-in times.

However, Airbnb has denied such claims, telling DW: "This data is wrong and uses flawed methodology to make false conclusions. Airbnb has always been a platform where different types of accommodations can be listed, including boutique hotels & bed and breakfasts. The vast majority of hosts are home sharers, private people who occasionally rent out a room in their apartment or their entire homes when they are on vacation, on a business trip or need to commute between two cities."

Cologne has the biggest rate of Airbnb offers, with 1,154 overnight stays per 100,000 inhabitants, but Berlin has by far the biggest number of Airbnb offers overall: 38,500, a figure which shows how the platform has come to dominate the sector: the German capital's entire tourism industry offers 139,000 beds per night.

But the Berlin government believes it has the problem in check - having introduced a law in 2014 that forbids the commercial use of residential space for vacations (as well as demolishing residential property or leaving it empty and failing to put it on the market for more than six months). Berlin, like most German cities, is experiencing an acute shortage of affordable homes. Rents are rising at a rate of nearly 10 percent a year, even though the city has a rent cap and has introduced one of the strictest bans on holiday apartments - many other European cities also have some kind of regulation.

Saving the neighborhood

'The streets of Prague are empty in winter'

"The fact that renting through Airbnb or other platforms is on the rise, and is not by a long way just about home-sharers - that's a development that we've seen, and that's what the ban is for too," said Katrin Dietl, spokeswoman for the Berlin housing ministry. "We consider that law in line with the constitution, and we will continue to stick by it."

Some 60 public officials are tasked with policing Berlin's ban, with the power to impose fines for violations, and, according to Dietl, the ban has been successful: 2,500 former vacation apartments were put back into the regular rental market by the end of last year. Dietl says this is important. "If you look at Prague, you see that the center of the city is virtually empty during the winter, because no one really lives there anymore," she said.

But regular landlords also feel they have become collateral damage to the regulations. Maria Becher, spokeswoman for Haus & Grund, an association that represents landlords' interests, says they have been following the development of such bans in many countries. "We're very critical," she said. "We see that as a violation of private property. Our members own around seven apartments on average, they're not big companies."