Many owners find out about this rule too late — with the architectural design done, the contractor chosen and the price agreed. That's when someone asks: "what about the seismic assessment?". If the works require it and nobody planned for it, you lose time and money. If the works require it and nobody does it, the risk stays hidden inside the walls.
What the law says, in plain English
Portugal's building-refurbishment regime (Decree-Law No. 95/2019) left it to a ministerial order to define when works must assess how a building responds to an earthquake. That order is Portaria No. 302/2019 of 12 September, in force since 15 November 2019. Article 1 says that extension, alteration or reconstruction works require a seismic vulnerability assessment report — establishing the building's capacity against the seismic action of NP EN 1998-3:2017 (Eurocode 8, part 3) for the site conditions — whenever one of four conditions applies.
The 4 conditions that make the assessment mandatory
| Condition (art. 1(1)) | In practice, for example |
|---|---|
| a) Clear signs of structural deterioration | Structural cracks, exposed and corroded reinforcement, rotten timber floors, visible settlement |
| b) The works change the building's structural behaviour | Removing or opening up load-bearing walls, adding a storey, replacing timber floors with concrete slabs, a change of use with heavier loads |
| c) Intervention area above 25% of the gross floor area | A deep renovation across several floors of a building, counting demolitions and extensions |
| d) Cost of the works above 25% of building an equivalent new one | An "almost total" refurbishment, even without touching much of the area |
One of the four is enough. The trickiest is b): knocking the kitchen through to the living room looks like an interior job, but if the wall that comes down is load-bearing, the works are changing the building's structural behaviour.
Schools, hospitals and crowded buildings: the thresholds drop to 15%
Paragraph 2 of the same article tightens the rule for buildings in importance classes III and IV, as defined in NP EN 1998-1:2010 — broadly, buildings whose seismic resistance matters because of the consequences of a collapse (such as schools and assembly halls) or that are vital during an emergency (such as hospitals and fire stations). For them, the thresholds in c) and d) go down from 25% to 15%.
The 90% rule: when the assessment forces strengthening
The report isn't paperwork to file away. Under paragraph 3, when it concludes that the building does not meet the safety requirements for 90% of the seismic action defined in NP EN 1998-3, a seismic strengthening design becomes mandatory under the same standard. In plain terms: if the building scores below 90%, the works have to include the strengthening.
Why this matters for your budget: it's far better to know whether your works fall under these rules before you ask contractors for quotes. Strengthening discovered halfway through the works always costs more than strengthening planned in the design.
Did SIMPLEX 2.0 change anything?
SIMPLEX 2.0 (Decree-Law No. 108/2026 of 29 May) came into force on 1 October 2026, after Decree-Law No. 155-B/2026 postponed the original date. According to Cuatrecasas' analysis, it kept the philosophy of the 2024 regime, approved new templates for applications and for the termos de responsabilidade (Portaria No. 320/2026/1) and cut the follow-up control period for prior notifications from 10 years to 1. It mainly changes how applications are filed and checked — and, with less prior control, it puts even more weight on whoever signs.
Portuguese engineers had already raised this: in 2023, experts interviewed by ECO pointed out that structural licensing does not require an independent technical check — it relies on the designer's termo de responsabilidade. A seismic assessment only protects you if it's done properly.
Why it isn't red tape: Portugal does shake
- On 26 August 2024, a magnitude 5.3 earthquake centred about 60 km west of Sines was felt in Greater Lisbon, Porto and the Setúbal district, according to IPMA as reported by RTP. There were no casualties or significant damage.
- On 19 February 2026, a magnitude 4.1 earthquake near Alenquer was felt across the Lisbon region (IPMA, as reported by A Bola), with no damage recorded.
- In the Lisbon Metropolitan Area, almost 68% of the 452,582 buildings were built before effective seismic legislation, and only 15% of homes in Portugal have seismic risk covered by insurance (figures cited by ECO in 2023).
- Lisbon City Council has assessed the seismic vulnerability of 1,593 buildings in municipal housing estates under its ReSist programme (ECO, June 2025).
What you get with our seismic vulnerability assessment
- Free remote pre-check: from plans, photos and a description of the works, we tell you whether they fall under one of the 4 conditions — and why.
- A site visit, scheduled and quoted upfront: survey of the structural system, materials, alterations made over time and signs of deterioration. We never assess a structure from photos alone.
- Modelling and verification against the NP EN 1998-3 seismic action for the site, with the conclusion on the 90% threshold.
- A signed report by an engineer registered with the Ordem dos Engenheiros and, if needed, the seismic strengthening design.
Real earthquake experience: after the magnitude 7.4 earthquake of 10 August 2026 in Colombia, our team published more than 40 post-earthquake structural assessments, case by case — on-site inspection, habitability classification and a signed report. It's the same inspection method we apply in Portugal. See the published assessments (in Spanish).
How much does it cost?
There's no public fee table for these assessments, and be wary of anyone who quotes without seeing the building: the price depends on the area, access, the structural system and whether testing is needed. Our approach is simple: the remote pre-check is free and, from the plans and photos, we send you a fixed quote within 48 hours. If your works also need a structural stability project, it starts at €800 for a house — see the prices on our services page or get an estimate with the calculator.
Sources: Portaria No. 302/2019 (Diário da República, in Portuguese) · Cuatrecasas, SIMPLEX 2.0 guide (Sep 2026) · RTP, 26 Aug 2024 earthquake · A Bola, 19 Feb 2026 earthquake · ECO, February 2023 · ECO, June 2025.