I am going to give you some technical-administrative advice to take into account before buying a home, especially an old one, that you have to reform:
Many integral reforms in Barcelona can become a real problem if certain things are not taken into account:
1.- Try to make a tasting (hole) in the false ceiling to see the state of the beams. You must know that the structure is a common element and that the repair must be borne by the community. The contribution that each neighbor must make is proportional to the coefficient of participation in community expenses. If you have already bought the house and you are already doing the reform, it can represent a significant delay in the work and an unforeseen economic expense that you will have to advance first so as not to delay the work that you have already started.
2.- Check that most of the apartments in the community are from different owners, and also how many apartments are rented in the community with respect to the totality. Be careful if most of the apartments are owned by the same owner. These apartments can be sold to a company whose objective is the rental of tourist apartments, with the possibility that later you may have coexistence problems, noise, etc.
3.- Before buying the house, try to obtain the community statutes and verify that they state that apartments cannot be made for tourist use. If it is stated, the Barcelona City Council does not grant activity licenses for that use.
4.- Try to go see the apartment at different times to check the internal and external noise there is. (Noisy neighbours, schools in the inner courtyard, activity in the premises on the ground floor, etc.)
5.- Check the state of the façade, the roof and the interior patios so as not to be surprised that in the short term they have to be rehabilitated and you have to take care of the spillovers to provide funds to carry out these improvements.
6.- Not all the premises on the ground floor can be converted into housing. Make a prior consultation to an expert or to l’Ajuntament. It can give you clues about the feasibility of that purchase if you consult the Cadastre (https://www1.sedecatastro.gob.es/OVCFrames.aspx?TIPO=CONSULTA) and check the built area that appears in the property data (not counting parking lots) and divide by 80. If the result is greater than the number of houses that already exist, there are many possibilities that a change of use can be made from premises to housing.
Finally, keep in mind that for little money, compared to the price of the house, you can have a report from a technician who will give you an objective answer to those questions that can later cause problems for you.