The four floor areas of your home

A home in Spain does not have one floor area: it has four. The usable area is what you walk on; the built area adds walls and partitions; the built area with common areas adds your share of the entrance, the stairs or the pool, and it is the one the Catastro (the Spanish land registry for tax) publishes; and buildability is how much the town plan allows to be built. The figure you see most often in listings is usually the largest, so before comparing prices per square metre, check which square metre you are looking at.

Why does a Spanish home have four floor areas?

Because each one answers a different question. The usable area tells you how much living space you have. The built area, how much the home takes up as a building. The built area with common areas, which share of the whole building is yours, which is what the Catastro values. And buildability, what can still be done with the plot.

The first three go from smallest to largest: each one adds something to the one before. The fourth is different. It does not measure what is there but what the town plan allows, which is why it never appears in a listing or in the Catastro.

If you are used to buying in the United Kingdom or northern Europe, where listings usually quote the internal floor area, this is the biggest surprise: in Spain, the headline figure often includes walls and a share of the pool.

What is the usable area?

It is what you walk on: the floor of the home measured from the inside face of the walls. It leaves out the space taken by partitions, walls and pillars, and any floor with less than 1.50 metres of clear height (the low part of an attic, for example).

Terraces depend on what the measurement is for. Under the Andalusian consumer information rules (Decreto 218/2005, de 11 de octubre) and for state-protected housing (Real Decreto 3148/1978, de 10 de noviembre), the usable area includes half of private terraces, bay windows and drying areas, with a cap: at most 10 % of the enclosed usable area. In a mortgage valuation, however, the usable area leaves outdoor spaces out and lists them separately (Orden ECO/805/2003, de 27 de marzo, the rules for valuations).

In Andalusia, a listing that describes the home must state its usable area. Decreto 218/2005 requires it from anyone selling or advertising as a professional. If a listing just says "square metres", ask which ones.

What is the built area?

It is the usable area without deducting the space taken by partitions, pillars and ducts, plus the outer walls: façade walls in full, and walls shared with a neighbour or the staircase at half. That is how Orden ECO/805/2003 defines it for valuations, and Decreto 218/2005 uses similar terms in Andalusia.

It is usually the figure in the title deed (escritura) and in the Land Registry, because it is the one declared when the building was registered.

Terraces count according to whether they are covered or enclosed. In the Catastro valuation rules (Real Decreto 1020/1993, de 25 de junio), they count like this:

That is why two penthouses that look identical can have different areas in the Catastro: it only takes one of them having a covered terrace.

What is the built area with common areas?

It is the built area plus your share of the common areas: entrance hall, stairs, landings, lift and, on an urbanisation, also the pool, gardens, roads, car parks and plant rooms.

It is the one the Catastro publishes and the one behind the cadastral value, which is the basis of IBI, the annual local property tax. It is also the one most listings show, because it is the largest of the three.

One important point: your share in the community of owners (the cuota de participación) is not worked out from this figure. The Horizontal Property Act (Ley 49/1960, de 21 de julio, article 5) takes as its basis the usable area of each flat in relation to the whole building, adjusted for its position, its situation and the expected use of the shared services. In fact the relationship runs the other way: the area with common areas is calculated by sharing out the common areas according to that quota.

What you pay towards community costs comes from the quota set in the building's founding deed (the título constitutivo, usually drawn up by the developer when the flats are first sold), and it does not change by itself even if you renovate your flat. The community's statutes can also share some costs differently: the law refers to "what has been specifically agreed" (article 9.1.e), which is what allows, for example, ground-floor owners not to pay for the lift. If a quota was set without following those criteria, you can ask for it to be corrected, with the agreement of all the owners or before a judge.

What is buildability?

It is what the town plan recognises: how many square metres can be built on a plot. Each municipality's general plan sets it (in Andalusia, within Ley 7/2021, de 1 de diciembre, the regional planning law; in the Madrid region, within Ley 9/2001, de 17 de julio, the regional land law).

It does not appear on any property portal or in the Catastro, and it decides whether you can extend, add a floor or enclose a terrace. If the plot has used up its buildability, there is no square metre to add, however much land or terrace you have.

In a building with a community of owners there is one more point: any buildability left belongs to the plot, not to your flat. Using it goes through the community, unless the founding deed says otherwise.

An example with figures

A flat on an urbanisation on the Costa del Sol, with indicative figures (they change from home to home):

The same flat costs 3,000 or more than 4,000 euros per square metre depending on which square metre you use. Comparing the price per metre of two homes only makes sense if both are measured the same way.

Before comparing prices per square metre, always ask which floor area is being quoted.

Where can you check each one?

• Usable: it is not in the Catastro. You get it by measuring, from the building project or from the title deed, if it breaks it down. In a new build, the developer's documents include it.
• Built: in the title deed and in the nota simple, the Land Registry extract any buyer should request.
• With common areas: on the IBI bill and on the Catastro's online office, which shows the private part and the common areas separately.
• Buildability: in the municipality's town plan, or through a planning report from the town hall. It is the only one of the four that normally needs an architect or surveyor to review it.

What if the Catastro, the deed and reality do not match?

It is common, especially in homes that have been renovated or have terraces enclosed years ago. It does not stop a sale, but you should spot it before agreeing a price and before signing a deposit contract (arras).

If the difference is only a measuring one, the Land Registry can correct it. Since Ley 13/2015, de 24 de junio, a difference of up to 10 % can be registered with the cadastral certificate, if it matches the property, and one of up to 5 % with no further procedure, as long as the registrar has no doubts. Beyond that, a formal file is needed, before a notary or at the Registry.

If the error is in the Catastro, you can report it so it is corrected. And if the difference comes from building work (an enclosed terrace, an extension), it has to be declared to the Catastro and legalised: with a licence or, if the town hall can no longer act against it, with a surveyor's certificate of age and a deed declaring the extension.

For a mortgage, the valuer measures the home and uses the area they verify. If they cannot verify it, they take the smaller of the Catastro and Registry figures, under Orden ECO/805/2003. A large mismatch can lower the valuation and, with it, what the bank will lend.

Enclosing a terrace: what to work out first

Enclosing a terrace is not just building work: it adds to your built area and, with it, to the cadastral value and your IBI. A covered terrace that counts at 50 % counts at 100 % as soon as it is enclosed on three of its four sides.

Before the work, three things have to be in place:

• Buildability: the town plan must allow those square metres. If the plot has used it up, no licence is possible.
• Town hall licence: the work goes through the town hall like any other that adds floor area.
• Community of owners: the Horizontal Property Act lists enclosing terraces among the works that alter the building (articles 10.3.b and 17.4 of Ley 49/1960), and requires the votes of three fifths of the owners, who must also hold three fifths of the shares.

Afterwards, the work is declared to the Catastro, which updates the cadastral value. It is worth doing the sums before deciding, not after the first IBI bill.