Maresme listings are generous with the word casita. Sometimes it is a genuine second dwelling with its own kitchen and front door. Sometimes it is a pool room with a sofa bed and a shower nobody has used since 2019. The difference is not cosmetic, it decides who can legally live there.
In a Maresme listing you will meet casa de invitados, casita, annex, vivienda independiente, apartamento de invitados and, in older houses, habitación de servicio. Sizes run from about 25 m² to 90 m². A real guest house has four things: a separate entrance from the street or garden, a kitchen, a bathroom and a door that closes between it and the main house. If one of those is missing, you are looking at a room, not a dwelling.
At the top of the market the product is real. Estates in Supermaresme and around Sant Vicenç de Montalt, Llavaneres and Cabrils are sometimes let as a main house of 500 m² plus a guest house of 70 m², with the two connected by the garden rather than a corridor. That layout is what most families are actually looking for when they ask for two houses.
The cédula d'habitabilitat is issued per dwelling, not per plot. Ask how many the property has. If the answer is two, the guest house is a legal dwelling with its own address: your mother can register on the padrón there, and in principle it could be let separately, subject to the licence and the community. If the answer is one, the casita is a dependencia. It is perfectly fine to house a relative or an au pair. It is not a legal dwelling, and nobody can claim it as their address.
Four documents settle the question faster than any agent's description: the cédula or cédulas, the Nota Simple (one finca or two), the catastro reference (one or two) and the utility meters. Separate electricity and water meters are the clearest physical sign that somebody once intended the annex to stand on its own.
What it is not good for: earning rent. Tourist letting needs a HUT licence, and most Maresme towns are restrictive about new ones. A long-term sublet needs the owner's written consent under article 8 of the LAU. And a dependencia without its own cédula cannot be let as housing at all, whatever the previous tenant did.
Expect a premium of roughly 10 to 25% over the same house without an annex. In the current long-term market, a main house of four or five bedrooms with a guest house in Llavaneres, Cabrils, Teià or Sant Vicenç generally asks €5,500 to €9,000 a month; front-line sea properties go past €12,000; smaller inland houses or the north of the comarca can sit at €3,000 to €4,500. Below that band you are usually looking at a house where the casita is a converted garage.
The running costs are less obvious. An extra 40 to 90 m² means more heating, more hot water, another fridge and another washing machine. In a house with one boiler and one electrical supply, the annex does not add a fixed monthly fee so much as a permanent extra load. Budget €150 to €400 a month on top of the main house, more in winter if the guest house has electric radiators and single glazing.
The annex has to be named in the contract, with its own inventory. Not "the property includes an annex" in an annexe nobody reads, but the rooms, the furniture and the meter readings in the document you sign. If the owner keeps a set of keys for storage, say so in writing and price the house as if the space did not exist.
Settle three splits before signing: who cleans the guest house, who pays for its utilities if there is no sub-meter, and who is responsible for the roof and gutters above it. On a two-building property, "the tenant maintains the garden" can quietly grow into two gardens, a shared pool and a boundary hedge.
Insurance is the one people forget. Your renter's policy should name the annex and its contents, and the owner's building policy should cover both structures. If a guest house is excluded from the owner's cover, a burst pipe there is a conversation you do not want in November.
Walk away if the annex has no cédula and the owner still wants it in the rent as living space, if the only route to it is through the main house, or if you need its rent to make the numbers work. A guest house is a convenience for a household that already fits the main house. It is a poor substitute for a second home, and a worse one for income.
Tell us who needs the second building and what for. We know which Maresme estates actually have a legal second dwelling, which ones only have a converted garage, and what the difference should cost you.
Ask about villas with an annex Download the villa viewing checklist (PDF)