According to the rule enacted by the regional government of Madrid, one has to rent a short term vacation rental in private apartments for a minimum stay of five consecutive nights. In part, this rule attempts to limit growth of services like Airbnb.
According to official estimates, Madrid region has between 6,000 and 8,000 homes for tourism use, which are let out using web channels. The new regulation mandates that short term rentals need to register themselves with the Government before advertising. Airbnb and homeaway may not be complying with the regulations. Other smaller providers get away by booking guests for 5 nights for the price of 3 nights. You need to be careful while booking short term holiday apartment.