How exposed to earthquakes is the building you want to buy?

What is basic seismic acceleration?

It is the figure Spain's earthquake-resistant building code, NCSE-02, published in the BOE in 2002, uses to measure the hazard of each place: the horizontal acceleration of the ground, expressed as a fraction of gravity (g). Its annex 1 gives it, with the coefficient K, for every municipality at 0.04 g or more.

Spain's earthquake-resistant building code (NCSE-02) describes the hazard of each place by its basic seismic acceleration: a characteristic value of the horizontal acceleration of the ground, expressed as a fraction of gravity (g). It comes with a contribution coefficient, K, which reflects the different kinds of earthquake expected. Annex 1 of the code gives both values for every municipality with an acceleration of 0.04 g or more.

That 0.04 g is the first threshold: below it, the code does not apply to buildings of normal importance, those that, like a block of flats, could cause casualties if they collapsed. Up to 0.08 g it does not apply either to buildings with frame structures well braced in every direction, unless they have more than seven storeys and a design acceleration of 0.08 g or more. Above that, the code sets specific limits: for example, brick masonry buildings may have at most four storeys between 0.08 g and 0.12 g, and two from 0.12 g.

Where the hazard is highest

In the south and south-east of mainland Spain and in the Pyrenees, according to the Spanish National Geographic Institute (IGN). In the NCSE-02 annex, Granada has 0.23 g, Murcia and Elche 0.15 g, Almería 0.14 g and Málaga 0.11 g, against 0.04 g in Barcelona; Madrid falls below that threshold.

According to the hazard study of Spain's National Geographic Institute (IGN), earthquakes on the Spanish mainland cluster in the south and south-east and in the Pyrenees. The belt that follows the south-east coast, with the Carboneras, Alhama de Murcia, Carrascoy and Bajo Segura faults, has intense seismic activity.

The NCSE-02 annex puts figures on it. Granada has 0.23 g; Orihuela, 0.16 g; Murcia and Elche, 0.15 g; Almería and Torrevieja, 0.14 g; Lorca, 0.12 g; and Málaga, 0.11 g. At the other end, Barcelona has 0.04 g, Valencia 0.06 g and Seville 0.07 g, and Madrid is not on the list because its value is below 0.04 g.

In 2016 the IGN published a newer map, the one in the Spanish National Annex to Eurocode 8 (UNE-EN 1998), which gives the peak ground acceleration for any point with a 475-year return period, plus its K coefficient. That is the map the HOUSINGFAX report uses, so its figure may not match the one in the NCSE-02 annex.

Which code applied in the building's year?

It depends on the date of the design: first came the PDS-1 code of 1974; the NCSE-94 was published in the BOE on 8 February 1995 and the NCSE-02 on 11 October 2002. Each change allowed two years of overlap, so the year of construction in the Catastro is a guide, not the answer.

The first stage is the PDS-1 code, approved by Decree 3209/1974 of 30 August. NCSE-94 was published in the Official Gazette on 8 February 1995 and for two years coexisted with PDS-1: new projects could follow either. NCSE-02 was published on 11 October 2002, with another two years in which NCSE-94 could still be used.

That is why the year of construction published by the Catastro (Spain's property register of buildings) is a guide, not a verdict. What counts is the date of the design, which is usually earlier than the date the works finished: a building completed in 1996 may have been designed under PDS-1. The year also does not tell you whether the structure was strengthened later.

What it means for a buyer

In a low-hazard area, the building's year matters little for this question. In Granada, Murcia, southern Alicante or Almería, a building designed before NCSE-94 was not calculated to today's requirements. That does not make it unsafe: it means it is worth knowing how its structure is built and whether it has had strengthening works.

Ask the owners' association (comunidad de propietarios) about the building's original design and any structural works, ask for the latest building inspection (ITE or IEE) and, if you plan to remove load-bearing partitions, walls or columns, talk to a surveyor or structural engineer first. In a multi-storey brick block in a 0.08 g zone or above, that conversation matters even more.

How HOUSINGFAX checks it: check 12

Check 12 of the report answers “How seismic is the area?”. It takes the reference acceleration at the building's location and its K coefficient from the IGN's 2016 map and turns them into a level in words: low below 0.04 g, moderate up to 0.08 g and high from 0.08 g, which the report flags as worth noting. It then places the building under its code according to the Catastro year of construction: before PDS-1, under PDS-1, under NCSE-94 or under NCSE-02.

Start with the free report: it shows the check with your building's real data and the key information blurred. To see it in full, the essential report costs €11 and the complete report, which adds the recorded building condition, €19. That is 22 checks on official sources, as a PDF in a few minutes, with a single payment and no account. The report does not replace a technical inspection of the building.