If you would like to rent your property in Spain for long term, the requirements are:
If you would like to use your property in Spain for short-term rental, many city councils such as Barcelona require you to register your property. (Hotels are complaining that they have strict regulations, then short-term rental units should have these regulations too.)
A unit is defined as short-term if the renter can sign up immediately for a slot sometime in the future, for a period of days, weeks, or months (up to 3 months), usually via third-party websites. The regulations term such a rental unit as a "tourist apartment". Renting a room in your house is generally not subject to these regulations.
Catalunya government FAQs about renting out your property (English)
Our service includes the following:
If there is an inspection of the property, and it is determined that renovations are required, the city council imposes a tax of 3,35% on the cost of the renovation.
In Catalunya, when you advertise your property on an online site such as airbnb.com, you are required to list your registration number as part of the desciption of your property. You may be fined if this is not done.
For more information regarding our property registration service, please contact us.
This varies depending on the city council, but in Barcelona it takes only a few days after submitting all the required documents. Afterwards, though, there might be an inspection once the documents are sent on to the technicians.
Please note that the Barcelona City Hall no longer grants new licences in the district of Ciutat Vella (including the Born). The only option to get a licence would be to buy an apartment that already has a licence, and use that licence instead for the new apartment.