Sharing a flat to cut the rent is normal in Barcelona. Doing it as a formal sublet is a different thing, and most tenants get it wrong because they never read one clause. Here is how the subarriendo rule works, what written consent has to say, and where people slip.
Article 8.2 of the Ley de Arrendamientos Urbanos is short. A tenant can sublet only part of the home, and only with the landlord's prior written consent. Sublet the whole flat, or do it on a verbal nod, and you are in breach of the lease. The landlord can then move to terminate your contract.
That distinction matters, because "my landlord is fine with it" is not consent in the legal sense. It has to be written, and it has to be specific.
The law allows subletting a room or a defined part of the dwelling. It does not allow handing the entire property to someone else and walking away. That second move, ceding the whole home, is a different legal act (cesión), and article 8 wants written consent for it too, usually harder to get.
In practice most expat sublets are a spare bedroom in a larger flat, or an annex with its own entrance. Keep the arrangement partial and documented, and you stay inside what the article permits.
Ask for permission in writing before anyone moves in. A line in the lease works, or a separate signed authorisation. It should name the part of the home being sublet, the period, and ideally the person moving in. A text from the landlord is better than nothing, but a signed clause is what a judge will want to see.
You cannot use a sublet to make a profit on the gap. The rent you charge the subtenant cannot exceed the share of your own rent for that space. Charge a room at more than its slice of the whole and the arrangement is on shaky ground if it ever reaches a court. Subletting is for sharing costs, not for running a small business.
Subletting gives you a place to live, not the protection of a head tenant. Your rights end when the main lease ends, and your contract is with the head tenant, not the owner. If the head tenant stops paying, you can be asked to leave even though you paid every month. Before you sign a sublease in Barcelona, look at the main lease and the written consent, and keep a copy of both.
Turning a rented room into a de facto tourist stay is where this goes badly wrong. Barcelona restricts tourist letting hard, and a room marketed a few nights at a time can breach both the lease and local rules. If you want short stays, use a seasonal contract with the owner's knowledge, not a sublet dressed up as one.
City flats often ban subletting outright, so read clause by clause. Villas and larger homes in the Maresme are sometimes more relaxed, because a family renting a big house may genuinely want an annex for guests or staff. When we place a tenant in a Maresme villa, subletting is one of the clauses we flag before signing, in both directions.
If you are the owner, the same article protects you: you can refuse, agree partially, or agree with conditions. Put it in writing and you keep control of your property.