Building tolerances for homes

The “Save Home” law introduced important changes to the Presidential Decree. 380/2001, in particular regarding the so-called "construction tolerances" for homes. This term refers to the acceptable differences between the original design of a building and its actual construction.

The new legislation, rewriting article 34 bis of the Presidential Decree. 380/2001, has expanded the limits of these tolerances, distinguishing between "constructive" ones (variations compared to the project) and "executive" ones (small irregularities during the works that do not compromise the safety of the building).

The law has substantially redefined the limits within which variations compared to the original project are considered acceptable, introducing a complex system that takes into account the date of completion of the works and the surface area of ​​the buildings.

In this guide, we will explore the new features of the Save Home in detail, analyzing how to calculate the tolerances, what the special cases are and what changes for listed properties and seismic zones.

Regimes for building tolerances

One of the main innovations is the introduction of two distinct regimes for tolerances, based on the date of completion of the works.

General regime

For all interventions, the rule remains valid that deviations of up to 2% in measurements (height, distances, volume, surface area) compared to the approved project do not constitute building violations.

More favorable regime (for interventions by 24 May 2024)

The law provides wider tolerances for work completed by May 24, 2024.

These tolerances are inversely proportional to the surface area of ​​the property: the larger the property, the smaller the tolerance allowed.

Here are the new ones tolerance thresholds:

• 2% for properties over 500 square meters;
• 3% for properties between 300 and 500 square meters;
• 4% for properties between 100 and 300 square meters;
• 5% for properties under 100 square meters;
• 6% for properties under 60 square meters.

Simply put, “Salva Casa” recognized that, especially in older buildings or during complex works, small differences from the original design may occur. To avoid automatically considering these variations as building violations, the law has defined margins of tolerance. Furthermore, to accommodate past situations, prior to May 24, 2024, it has implemented a scale of percentage values ​​that especially protects smaller properties.

Why these differences in tolerances? 

The Ministry of Infrastructure and Transport (MIT), in its guidelines, helps us understand the reason for this distinction in tolerances. Although these guidelines do not have the force of law, they were created to help municipal technicians apply the new rules uniformly.

The legislator's choice to favor interventions carried out by 24 May 2024 is based on two main reasons:

• prevent future abuse: we want to avoid that, after the introduction of the new law, the wider margins of tolerance are intentionally exploited to carry out interventions that differ from the approved projects;
• recognize technical progress: construction techniques have improved over time. This means that, for recent interventions, it is less likely to find large differences compared to the original projects.

How is the useful surface for tolerances calculated?

Another important question that the guidelines of the Ministry of Infrastructure and Transport (MIT) have answered is: how to calculate the useful surface to determine the allowed tolerances?

The MIT clarifies that the useful surface area is defined by the Standard Building Regulations. In particular, it is the «floor surface area of ​​the spaces of a real estate unit, measured net of walls, pillars, partitions, recesses, door and window spaces».

Furthermore, the guidelines specify that for the calculation of tolerances the surface indicated in the original permit must always be considered, without taking into account any subdivisions that have occurred over time.

This clarification is a sort of guarantee to avoid that, through subsequent subdivisions, more favorable tolerance percentages can be applied which, when added together, would lead to significant discrepancies compared to the initial project.

It is essential to note that this rule applies only to interventions regulated by paragraph 1-encore of article 34 encore of the Presidential Decree 380/2001, i.e. those carried out by 24 May 2024.

In simple words, to calculate tolerances, the internal walkable surface area of ​​the property is considered, excluding walls and other structural elements, as indicated in the original project. It is unknown how the property may have been divided over time, to ensure that tolerances are not overused. This calculation system is valid only for works done before May 24, 2024.

Tolerances and hygienic-sanitary requirements: what changes?

When it comes to respecting hygiene and health standards and minimum distances, the guidelines of the Ministry of Infrastructure and Transport (MIT) are very clear: the tolerances are more stringent.

If the differences compared to the project concern the minimum measures established for distances or hygiene-sanitary requirements, the 2% tolerance (paragraph 1 of the article) always applies, regardless of the date of 24 May 2024. This means that the wider tolerances foreseen for interventions prior to that date do not apply.

The situation is different regarding the usability of buildings, in particular the relationship between paragraph 1-ter and article 24 of the Presidential Decree. 380/2001. In this case, the guidelines provide specific guidance for existing buildings:

• if the project was drawn up after 28 July 2024 (date of entry into force of law 105/2024), the new minimum measures defined by article 24 can be considered. The 2% tolerance is calculated on these new parameters;
• if, however, the project was drawn up before 28 July 2024, any differences must be assessed based on the minimum measures in force at the time the project was drawn up.

In summary, the tolerances for hygiene-sanitary issues and distances always remain the most restrictive of 2% regardless of the date of the works. As far as usability is concerned, everything is diversified based on the drafting date of the project. This is to ensure that safety and hygiene standards are always respected, even in the presence of small variations compared to the original project.

Construction tolerances and landscape authorization

According to the MIT, the interventions that fall within the "increased" tolerances (those of paragraph 1-encore of article 34-encore of the Presidential Decree 380/2001, valid for works by 24 May 2024) do not require landscape authorisation. This applies provided that they are works listed in Annex "A" of the Presidential Decree. 31/2017 and in article 4 of the same decree.

Executive tolerances and restricted properties

The situation is different for "executive tolerances" (small irregularities during work). The “Save Home” law applies the exemption from landscape authorization only to construction tolerances, not to executive ones.

Working tolerances include:

• smaller dimensions of the building;
• failure to implement non-structural architectural elements;
• irregularities of external and internal walls;
• different position of internal openings;
• errors in routine maintenance;
• design errors corrected on site;
• material errors in design representation.

Accordingly, enforcement tolerances do not apply to properties subject to landscape constraints (Legislative Decree 42/2004). Any irregularities in these properties must be remedied with ordinary procedures.

In summary:

• the manufacturing tolerances “increased” can avoid landscape authorization, under certain conditions;
• the executive tolerances do not enjoy this relief, especially for listed properties, which remain subject to normal amnesty procedures.