Earthquake risk in a Portuguese property is decided by the building more than by its postcode. The ground sets how hard a region can shake; the structure, its era and every alteration made since decide how that building responds. 68% of the buildings in the Área Metropolitana de Lisboa predate the seismic-protection legislation approved in 1958 (Público, February 2023), and since Decreto-Lei n.º 10/2024 nobody checks a building against its drawings before the deed. A buyer can still find out a great deal: the structural system, the walls that were removed, and whether renovation works triggered a seismic vulnerability report under Decreto-Lei n.º 95/2019. Our structural and seismic inspection guide covers the engineer's method; this article covers what you can establish before you commit, and when an InspectOS Structural & Seismic inspection answers the rest.
Table of Contents
- Is it risky to buy an older property in Portugal because of earthquakes?
- What does the location decide, and what does the building decide?
- Which structural system are you buying, and how can you tell?
- Which alterations change how a building behaves in an earthquake?
- Did a renovation trigger a seismic vulnerability report you can ask for?
- What an inspection adds to the paperwork
- Frequently Asked Questions
Is it risky to buy an older property in Portugal because of earthquakes?
Seismic risk in an older Portuguese property varies building by building, set by the structure and its alterations more than by the address.
Portugal has a documented seismic history. The earthquake of 1 November 1755 destroyed much of Lisbon and produced the building type the Baixa is still made of. Two tremors were felt in the Lisbon region in 2026: a magnitude 4.1 event with its epicentre near Alenquer on 19 February (IPMA), and a magnitude 3.3 event near Cadaval on 10 August, which caused no damage (Público, 10 August 2026).
Nobody can tell you when the next significant earthquake will happen, and any article that offers a probability for a specific building is guessing. The useful question for a buyer is narrower. Given the property on the table, what is known about how it was built, what has been done to it, and what documents exist?
Those three things can differ between two flats on the same street. Two buildings of the same age can sit at opposite ends of the risk range because one kept its original structure and the other lost half its internal walls to an open-plan renovation.
What does the location decide, and what does the building decide?
The national seismic zoning in NP EN 1998-1 and the local ground type set the shaking; the building's structural system and condition set the damage.
Eurocode 8 (NP EN 1998-1, with its Portuguese national annex) maps the country into seismic zones for two scenarios: a large, distant earthquake offshore, and a moderate one close by. Soil adds a second layer. Soft ground, such as the river alluvium under parts of the Baixa, amplifies shaking compared with rock a short distance away. A buyer cannot change either, and a detailed regional map belongs to a desktop check rather than a building inspection.
Everything else sits inside the property boundary. The structural system decides how loads travel when the ground moves. The condition of that system decides whether it still works as designed. Alterations decide whether it is still the system the original builder put there.
That is the part a buyer can investigate, and it is where the difference between two neighbouring buildings comes from.
Which structural system are you buying, and how can you tell?
Portuguese buildings fall into recognisable structural systems by era, from the timber gaiola pombalina to reinforced concrete frames designed to the 1983 RSA code.
The construction era predicts the structural system with reasonable accuracy, and our guide to structural risks in Portuguese houses by build era maps each period to its characteristic failure. In short: pombalino buildings from after 1755 carry a braced timber frame, the gaiola pombalina, inside their masonry; gaioleiro buildings from about 1890 to 1930 kept the masonry and dropped the frame; mid-century buildings added concrete floor slabs, the placa, to masonry walls; later stock moved to reinforced concrete frames, with seismic design becoming routine from about 1990, after the Regulamento de Segurança e Ações (RSA, Decreto-Lei n.º 235/83, de 31 de maio).
Four sources tell you which one you are standing in:
- The construction year on the Caderneta Predial Urbana and the date of the licença de utilização, read with caution, because both can record a later works date rather than the original construction.
- Wall thickness at window reveals. Thick, tapering masonry points to the older systems; thin infill between columns points to a concrete frame.
- The floors. Timber floors flex and sound hollow; a placa is rigid and often shows its edge at a balcony or stairwell.
- Columns and beams visible in a basement, garage or ground-floor shop.
The era is a starting point. Concrete from before the 1983 code carries its own durability questions, covered in our guide to concrete cancer in Portuguese buildings.
Which alterations change how a building behaves in an earthquake?
Removed walls, widened ground-floor openings, added storeys and heavy new floors change seismic behaviour, and none of them is visible once the finishes go back.
A building's resistance to an earthquake depends on walls and frames that carry sideways load. Renovations remove, cut or overload those same elements, and a fresh finish hides the result. These are the alterations an engineer looks for first:
- Internal walls removed for open-plan living. In a pombalino building the internal walls are the frontais, carrying the diagonal bracing of the cage. Taking one out removes part of the seismic system. A long, unbroken ceiling in an old building is a question worth asking.
- Openings cut or widened in load-bearing walls. New doorways, arches and kitchen pass-throughs reduce the wall that resists lateral load.
- Ground floors opened up. Shopfronts, garages and open-plan ground floors with the walls taken out leave the upper storeys standing on a weaker base. In an apartment building this may have happened in a fraction you are not buying, and it still affects yours.
- Storeys and attics added. An extra floor or a converted roof space adds mass at the top of the building, which is where it does the most harm in an earthquake.
- Heavy new floors on old structure. A concrete screed or slab poured over timber joists adds weight the original walls were not built to carry.
- Rotten timber at the wall ends. Joists and frame members decay where water reaches them, most often at roof and party-wall junctions. Our Lisbon apartment inspection guide covers where to look.
Some of these works needed a municipal licence and never received one. Our guide to spotting illegal extensions before you offer covers the desk checks, and the owner of an unlicensed alteration faces fines under the RJUE (Decreto-Lei n.º 555/99). Those consequences pass to the buyer with the property.
Did a renovation trigger a seismic vulnerability report you can ask for?
Since 15 November 2019, major renovation works trigger a seismic vulnerability report under Decreto-Lei n.º 95/2019, Article 8, and Portaria n.º 302/2019.
Article 8 of Decreto-Lei n.º 95/2019, de 18 de julho, makes extension, alteration and reconstruction works subject to a seismic vulnerability assessment report (relatório de avaliação de vulnerabilidade sísmica). Portaria n.º 302/2019, de 12 de setembro, sets when it applies. Both entered into force on 15 November 2019. The report is required when the works meet any one of four conditions:
- The structure shows evident signs of degradation.
- The works change, or have the effect of changing, the building's structural behaviour.
- The area intervened, including demolition and extension, exceeds 25% of the building's gross construction area.
- The construction cost exceeds 25% of the cost of an equivalent new building.
For buildings in importance classes III and IV under NP EN 1998-1, such as schools and hospitals, both percentage thresholds fall to 15%. If the report concludes the building does not meet the safety requirements for 90% of the seismic action defined in NP EN 1998-3:2017, a seismic reinforcement project (projeto de reforço sísmico) becomes mandatory.
For a buyer, two points follow. The report attaches to works, never to a sale: a seller with no planned works has no duty to produce one. And a building that went through heavy rehabilitation after November 2019 may well have one in its licensing file at the Câmara Municipal. Ask the seller, or the condominium administrator for a whole-building renovation. If the building was gutted and rebuilt inside after 2019 and no report exists, that absence is a question for the seller and for the municipal file, not proof of a problem.
The paperwork has limits in the other direction too. Since 1 January 2024, under Decreto-Lei n.º 10/2024, de 8 de janeiro, the notary no longer checks the licença de utilização at the deed. Since 1 October 2026, the deed records whether an urban planning title (título urbanístico) exists, under Decreto-Lei n.º 108/2026. Neither step compares the building with its drawings. Our habitation licence guide covers the three record checks a buyer can run.
What an inspection adds to the paperwork
An OE-registered engineer reads the structural system, the alterations and the condition on site, then says whether a full seismic assessment is warranted.
Documents tell you what was approved. A site visit tells you what is there. In an InspectOS Structural & Seismic inspection, a civil engineer registered with the Ordem dos Engenheiros (OE) identifies the structural system, looks for removed or cut walls and added mass, reads cracking by its pattern and location, checks timber and concrete where access allows, and compares what is standing with the licensed drawings when the buyer can obtain them.
One limit matters here. A pre-purchase visit does not replace a full assessment to NP EN 1998-3, which involves investigation and structural modelling. It tells you whether that assessment is needed, and whether the building on offer is still the building that was designed. That answer is what lets you negotiate, budget for reinforcement or walk away before the CPCV binds you. The Structural & Seismic service page sets out the scope.
The inspection screens for unlicensed structural alterations, which carry fines under the RJUE and become the new owner's problem at the deed.
Frequently Asked Questions
Is it safe to buy an old apartment in Lisbon because of earthquakes?
It depends on the building, not the city. Seismic zoning and soil set how hard the ground can shake, but the structural system, its condition and the alterations made since decide how a particular building responds. An engineer can tell you which system you are buying and whether it has been weakened.
Does the seller have to provide a seismic report when selling?
No. Portaria n.º 302/2019 attaches the seismic vulnerability report to extension, alteration and reconstruction works, never to a sale. A building that went through major works after 15 November 2019 may have one in its licensing file, and asking for it is reasonable.
Are newer Portuguese buildings automatically safer in an earthquake?
Buildings designed after the RSA code of 1983 follow seismic design rules, and that practice became routine from about 1990. Design rules do not guarantee execution, and later alterations can undo them. A 1995 building with its ground floor opened into a shop needs the same questions as an older one.
Can an older building be strengthened after I buy it?
Yes, and the law pushes in that direction when you renovate. If your works meet one of the Portaria n.º 302/2019 triggers, a seismic vulnerability report is required, and a reinforcement project follows when the building falls below 90% of the seismic action in NP EN 1998-3:2017.
How much does a structural and seismic inspection cost?
The price depends on the property type, size, access and distance, so InspectOS quotes per property at inspectos.pt/en/home-inspections. Set it against the RJUE fine exposure for unlicensed structural works, which transfers with the property at the deed.
Conclusion
Earthquake risk is a property of the building you buy: its structure, its condition and what previous owners did to it. The documents show part of that story and a site visit shows the rest. Book an InspectOS Structural & Seismic inspection before the CPCV, while the answer can still change the price or the decision.
→ Book a Structural & Seismic inspection · get a quote at inspectos.pt/en/home-inspections
Updated October 2026 | InspectOS Portugal · Legal references last reviewed 24 September 2026
Sources: Decreto-Lei n.º 95/2019, de 18 de julho, Article 8 (in force 15 November 2019) · Portaria n.º 302/2019, de 12 de setembro, Article 1 (in force 15 November 2019) · NP EN 1998-1 and NP EN 1998-3:2017 (Eurocode 8) · Decreto-Lei n.º 235/83, de 31 de maio (RSA) · Decreto-Lei n.º 555/99 (RJUE), fine ranges · Decreto-Lei n.º 10/2024, de 8 de janeiro · Decreto-Lei n.º 108/2026, in force 1 October 2026 (Decreto-Lei n.º 155-B/2026) · Público, February 2023 (Área Metropolitana de Lisboa building stock and the 1958 legislation) · IPMA, 19 February 2026 (Alenquer, M4.1) · Público, 10 August 2026 (Cadaval, M3.3)