D.M. 58/2017: the Sismabonus and the seismic-risk classes

From the territory to the building: the risk, not the zone

Seismic classification (OPCM 3274/2003) tells how hazardous the territory is; D.M. 58/2017 introduces something different: the seismic-risk class of the individual building. Risk depends on the site's hazard but also on the building's vulnerability and its exposure. A well-built building in Zone 1 may have a better class than a fragile one in Zone 3.

Eight classes, from A+ to G

The Guidelines classify risk into eight classes, from A+ (lowest risk) to G (highest). It is a scale as readable as the energy one, but referring to seismic safety.

How it is measured: PAM and IS-V

The class arises from two parameters. The PAM (expected average annual loss) measures the expected cost of damage, year by year: the economic side. The IS-V (structural safety index) measures how close the building is to the required safety level: the life-safety side. The final class takes the worse of the two assessments.

Two methods: conventional and simplified

There are two ways to assign the class. The conventional method, based on PAM and IS-V, applies to all building types and can certify even large improvements. The simplified method, reserved for masonry, rests on a quicker typological assessment, but can only attest the current class or a limited improvement. Choosing the wrong method may under- or over-state the result.

The Sismabonus: the incentive tied to the class jump

Classification is not an end in itself: it is the basis of the Sismabonus, the tax deduction for seismic-risk-reduction works. The benefit grows with the number of risk classes gained through the works (one or two) and is greater in apartment blocks. The pivot is the designer's sworn statement, certifying the class before and after: an untruthful statement causes loss of the benefit and entails liability.

Its place in the system

D.M. 58/2017 completes the seismic picture: OPCM 3274/2003 classifies the territory, NTC 2018 set how to design and verify, Circular 7/2019 explains how to apply them to existing buildings, and the Guidelines translate it all into an understandable risk class and an incentive. It is the level at which seismic safety becomes a readable value — for the owner, the market and prevention policy.

Why it matters

Making the existing stock safe is Italy's great seismic challenge. D.M. 58/2017 gives it a grammar and an incentive: it turns a technical concept — vulnerability — into a class anyone can understand and into a convenience that pushes people to act. For an architecture of the existing, it is the tool that ties safety, value and responsibility.