Insights
Seismic retrofit of existing buildings: when the law requires it and how it is done
An owner preparing a refurbishment needs to settle the budget. Before choosing seismic strengthening for an existing building, establish whether the works require a seismic vulnerability assessment report. The scope of work, structural condition and extent of the intervention matter; the building’s age alone does not answer the question.
When the report is mandatory
Portaria 302/2019, effective from 15 November 2019, sets criteria for extension, alteration or reconstruction works. Under Article 1(1), at least one of these conditions must apply:
- evident signs of structural deterioration;
- works that change, or have the effect of changing, structural behaviour;
- the area affected, including demolition and extensions, exceeds 25% of the building’s gross construction area;
- the cost criterion in paragraph (d), retained here in the original to preserve its precise comparison: «Cujo custo de construção exceda em pelo menos 25 % do custo de construção nova de edifício equivalente».
For importance classes III and IV under NP EN 1998-1:2010, the area and cost thresholds are reduced to 15%. Deterioration and changes in structural behaviour remain independent conditions without those thresholds. The Portaria does not restrict these criteria to residential use. Without the specified works, deterioration alone does not trigger this report requirement under this Portaria; other safety duties still need consideration.
When a strengthening design is required
Article 1(3) requires a strengthening design where the report concludes that the building does not meet safety requirements for 90% of the action defined in NP EN1998-3:2017. This percentage concerns seismic action, not a percentage of safety or a probability of collapse. The obligation to assess and the assessment result that requires a strengthening design are separate questions.
Article 9 of DL 10/2024 added Article 8(3) to DL 95/2019: the Portaria cannot confer powers on municipalities to appraise the report. This does not remove technical requirements. The applicable procedure and the engineer’s responsibility must be distinguished from municipal appraisal. Older proceedings also require checking the applicable transitional provisions.
What age and location can tell you
IPMA describes the 1909 Benavente earthquake as the largest in the twentieth century with an epicentre inside mainland Portugal. This provides regional context, not the design action or a diagnosis for an individual building.
Distinguish local seismic hazard, the building’s vulnerability and the consequences of an earthquake. The original design date helps direct investigations; it does not prove an older building was never strengthened or that a concrete building is safe. An open ground floor calls for examining the distribution of stiffness and strength before identifying a soft-storey mechanism.
How the assessment is carried out
Start by surveying geometry, materials, connections, damage and alterations. Check available drawings against the actual construction. The engineer defines inspections and tests and selects a method suited to the building type and available knowledge.
The Portaria refers to NP EN1998-3:2017 and subsequent updates. LNEC provides assessment guidance and methods, including simplified methods for specific building types. Their applicability must be checked; a single analysis model does not suit every building. The report should state assumptions, limitations and the assessment conclusion.
Strengthening options and their limits
Improving wall, floor and roof connections may form part of a masonry strengthening scheme. Anchorage and the capacity of the receiving elements need verification. Stiffening a floor also requires checking added weight and the resulting forces in walls and foundations.
Reinforced renders, fibre systems, concrete member jacketing, new resisting elements and foundation works are possible options, not prescriptions based on age or material. Selection depends on damage mechanisms, material compatibility, connections and overall structural response. Micropiles require a foundation intervention justified by the assessment and design.
Preparing the budget
Separate surveys and tests, assessment, design, strengthening construction and reinstatement of finishes. Occupancy, access and temporary works also affect the proposal.
Coordinating strengthening with refurbishment may avoid repeating some site setup or opening-up work. Savings require comparable quotations. There is no universal cost fraction, guaranteed increase in market value or guaranteed insurance advantage.
Frequently asked questions
Does every alteration require a report?
No. Extension, alteration or reconstruction works require checking at least one condition in Article 1 of Portaria 302/2019, including the specific thresholds for importance classes III and IV.
Is seismic strengthening always mandatory?
A strengthening design is mandatory when the report finds that safety requirements for 90% of the action defined in NP EN1998-3:2017 are not satisfied.
Is a reinforced concrete building safe?
Material and age alone cannot establish this. The structure, connections, condition and alterations need assessment.
What does strengthening cost?
Cost depends on the diagnosis and design. Distinguish assessment, design, construction, temporary works and reinstatement of finishes.
Before work starts
Do not remove walls or select strengthening solely from the building’s appearance. Gather available drawings and define the intended work so the engineer can establish the requirements and assessment scope. CertiAmb can coordinate this work with the engineering design and architecture. Contact the team to discuss the building.
This article is provided for information purposes only and does not constitute legal, tax or technical advice. Each situation should be assessed individually by a qualified professional.
