The 'Instructions' for applying the Technical Standards for Construction (D.M. 17/01/2018). Circular no. 7/2019 of the Superior Council of Public Works explains methods, formulas and examples, especially for existing buildings and seismic design, where the NTC are more concise. Published in Official Gazette no. 35 of 11 February 2019.
It accompanies the NTC 2018 across all structural fields, with particular emphasis on existing buildings (safety assessment, intervention categories, knowledge levels). It has no binding force of its own: it supplements and explains the NTC, which remain the binding reference.
The NTC 2018 are performance-based and concise: they say what must be guaranteed (safety, limit states) but leave the 'how' to the designer. Circular no. 7/2019 is the volume of instructions that makes them operable: it explains the methods, provides formulas, examples and criteria, especially where the NTC are densest — existing buildings and seismic design.
Its most important contribution concerns existing buildings, where the NTC are hard to apply 'to the letter'. The Circular details the safety assessment and the three categories of intervention, with criteria to understand when an intervention is required to reach full upgrading.
For existing buildings you do not start from theoretical designs but from the building as it is. The Circular ties the calculation to the level of knowledge achieved (geometry, construction details, materials): a lower level of knowledge means a more cautious confidence factor. The more you investigate, the less you are penalised: knowledge is part of the design.
| Level | In brief |
|---|---|
| LC1 (limited) | more cautious confidence factor |
| LC2 (adequate) | intermediate confidence |
| LC3 (accurate) | least penalty, extensive investigation |
Without the Circular, the NTC would remain a performance-based shell that is hard to fill, especially for existing buildings — which are most of Italy's built stock. It is the document that turns the principle into calculation and the calculation into site work, and that decides, in practice, how safe it is to intervene on the heritage we already inhabit.
It is not binding like the NTC: it is an authoritative interpretive reference; it is applied in practice, but alternative, equally valid and documented methods are allowed.
Improvement increases safety without reaching the level of a new building; upgrading brings the building to the level required for new construction. Upgrading is mandatory in specific cases.
In defined cases, for example raising the building, extensions interacting with the existing structure, changes of use that increase loads or the use class. In other cases improvement or a local intervention may suffice.
For existing buildings, the calculation depends on how well the building is known (geometry, details, materials): less knowledge means a more cautious confidence factor. Investigating more reduces the penalty.
It is their user manual: the NTC set the principles and the safety levels, the Circular explains how to apply them; they must be read together.