In short. What you can build on a plot is not decided by the architect or by the seller: it is decided by the planning rules (planeamiento urbanístico) of your municipality, through five parameters. Setback, buildable floor area, site coverage, height, and which floor area counts.
And a warning that saves grief: the Catastro tells you none of this. The Catastro is the registry kept for tax purposes, a different body from the Registro de la Propiedad (the Land Registry). The parameters live in the schedule of the zone by-law, another document in another place.
The five parameters, in order of surprises
Setback · retranqueo
The minimum distance the building must keep from each boundary of the plot: side boundaries, street frontage and rear.
It brings down more permits than any other, nearly always for the same reason: where it is measured from.
Buildable floor area · edificabilidad
The square metres you may build in total, adding up storeys. Usually expressed as a ratio applied to the plot area.
A ratio of 0.4 on 800 m² is 320 m² of buildable floor area.
Site coverage · ocupación
How much of the plot the building may stand on, as a percentage.
This is what decides whether the house goes on one storey or two.
Height and storeys
The maximum height to the cornice and the number of storeys allowed, which do not always go together.
Some by-laws allow a habitable roof space and others do not.
Countable floor area
What counts and what does not within the buildable floor area: basement, porch, terrace, roof space.
It is the parameter that wins or loses the most square metres, and the one least looked at.
The setback and the missing metre
The retranqueo, or setback, is the minimum distance between the building and a boundary of the plot. It is set by each town hall’s zone by-law and varies enormously: detached-housing zones with three metres to the side boundaries, and others with five, in the same city.
But the number is not usually the problem. The problem is where it is measured from:
- Many by-laws measure from the outermost point of the building. That brings in the overhang, the eaves and the cornice.
- Others measure from the plane of the façade, and overhangs have a separate rule of their own.
- Some include the part of the basement that stands proud of the ground.
- And some by-laws distinguish between side boundary, rear and frontage, with three different distances for the same house.
A metre of difference in a setback can bring a permit down, and the worst of it is that it shows up late, when the design is drawn and approved. Checking the exact definition before drawing costs an afternoon.
And do not confuse it with the distance for opening windows
Two independent rules, and both have to be met. The setback is a planning matter. The distance for opening windows facing a neighbour is civil: article 582 of the Civil Code requires two metres between the wall and the neighbouring property for direct views, and sixty centimetres for oblique views.
You can comply with the municipal setback and be in breach of the Civil Code. That is a neighbour’s claim, not a permit matter, and it arrives later.
Buildable floor area and site coverage: the pair almost everyone mixes up
They are two different limits and both apply at the same time. An example makes it obvious.
| Item | Value | What it means |
|---|---|---|
| Plot area | 800 m² | What you have bought |
| Buildable floor area ratio | 0.4 m²/m² | 320 m² buildable in total, adding up storeys |
| Maximum site coverage | 30 % | 240 m² maximum at ground level: what the house may stand on |
| Outcome A | 1 storey of 240 m² | It fits, but wastes 80 m² of buildable area |
| Outcome B | 2 storeys of 160 m² | You use the full 320 m² and free up garden |
| Outcome C | 240 + 80 m² | Ground floor at its maximum and a small first floor |
All three comply with the rules and give three radically different houses. That decision is design, not regulation, and exactly where an architect adds or subtracts value.
Countable floor area: where square metres are won
This is the parameter least looked at and the one that changes the result most. What counts within those 320 m² depends on the by-law, but the usual criteria are these:
| Element | Usual criterion |
|---|---|
| Basement wholly below ground | Does not count |
| Basement standing proud | May count in full or in part |
| Covered but open porch | Counts at 50 %, or does not count |
| Uncovered terrace | Does not count |
| Roof space | The part with enough clear height counts |
| Garage below ground | Usually does not count |
| Store rooms and plant rooms | Depends on whether they are below ground |
These criteria are the usual ones, not a rule. Every by-law defines them its own way and they have to be read in the schedule for your own zone. A porch that counts at 50 % in one municipality and does not count in the next one along is twenty square metres of difference in the house you can build.
Where you actually look these up
In order, and with the warning that matters:
The Catastro tells you what you have, not what you may do
The Catastro’s electronic office gives you the plot area, the referencia catastral (the plot’s registry reference) and what is already built. It is tax information.
It contains no buildable floor area, no site coverage and no setbacks. Starting here is fine; finishing here is the mistake. The estate agent’s listing is not binding either, and nor is the nota simple from the Registro de la Propiedad: that one covers ownership and charges.
The planning rules tell you what you may do
The municipality’s general plan, or its planning by-laws, assign your plot an ordenanza de zona, a zone by-law. That schedule holds the five parameters.
Almost every town hall publishes it, and most run a visor urbanístico too, an online planning map: enter the referencia catastral and it gives you the zone. Those are the official sources, not always easy to find. Land legislation comes from the region, the Comunidad de Madrid, but the plan and the schedule are the ayuntamiento’s: a separate administration, and the one that matters here.
And you have to check the constraints, which are not in the schedule
Rights of way, watercourses, roads, power lines, archaeological or drove-road protection, and aviation constraints.
These turn up late and cost the most, because they are not in the document everybody looks at.
What getting this wrong costs
This is the one mistake in a self-build that has no remedy. If you buy a plot counting on building 400 m² and the schedule allows you 250, there is no design, builder or budget that will solve it: you have paid for square metres that do not exist.
And once you know what fits, the next question is what it costs. The construction cost calculator adds it up with your town hall’s taxes, and ICIO by municipality sets out what each of them takes.
Frequently asked questions
What is a retranqueo, or setback?
The minimum distance the building has to leave from a boundary of the plot: the side boundaries with the neighbours, the street frontage or the rear. It is set by your town hall’s ordenanza de zona, the zone by-law, and it varies enormously between municipalities, and even between zones of the same one. It is not a national figure.
Where is it measured from?
This is the commonest mistake. Many by-laws measure from the outermost point of the building, and that takes in overhangs, eaves, cornices and in some cases the basement where it stands proud. Others measure from the façade. The difference can be a good metre, and a metre in a setback can bring down a permit.
Is the setback the same as the distance for opening windows?
No, and the two are confused all the time. They are independent rules and both must be met. The setback is a planning matter, set by the town hall. The distance for opening windows is civil: article 582 of the Civil Code (Código Civil) requires two metres between the wall and the neighbouring property for direct views and sixty centimetres for oblique views. You can meet the setback and still breach the Civil Code.
What is edificabilidad, or buildable floor area?
The square metres you may build in total, normally expressed as a ratio applied to the area of the plot. A ratio of 0.4 on a plot of 800 m² is 320 m² of buildable floor area. Careful: buildable floor area and site coverage are two different things.
Are edificabilidad and ocupación the same thing?
No. Edificabilidad (buildable floor area) caps the total built square metres adding up every storey. Ocupación (site coverage) caps how much of the plot the building may stand on. With 320 m² of buildable floor area and 30 % site coverage on a plot of 800 m², you may cover 240 m² at ground level: the house fits on one storey, or on two smaller ones with more garden.
Does the Catastro tell me what I can build?
No, and it is a confusion that costs money. The Catastro gives you the plot area and what is already built on it, which is tax information. What you may build is in the planning rules: the municipality’s general plan or its planning by-laws, and specifically in the schedule of the zone by-law that applies to your plot.
What counts towards buildable floor area?
It depends on the by-law, and it is where most is won or lost. Usually the basement does not count if it is buried, porches count at 50 % or do not count, uncovered terraces do not count and roof spaces count for the part with enough clear height. Change municipality and the criterion changes, and with it the house that fits.
Can I find all this out before I buy the plot?
Yes, and it is the most profitable thing you can do. Before signing you can look up the zone schedule, check the constraints and verify that what you have in mind really fits. It is the most expensive mistake in a self-build: by the time you find out you have already signed, and it is the only one with no remedy.
Send us the referencia catastral and we will tell you what fits
We come back with the buildable floor area, the maximum site coverage, the setbacks, the height allowed and the warnings we see: constraints, protected status or rights of way. It is signed by an architect, the professional who in Spain signs the design and applies for the permit.
If you have not bought yet, so much the better: that is when this is worth most. You can also see the houses we have built.