Construction tolerances in Italy: the 2-6% rule and how to declare them

Construction tolerances are the small differences between what was authorised and what was built that Italian law does not treat as building violations. A wall a few centimetres longer, an interior height that differs slightly from the design, a window set a little to one side: if they fall within the limits of Article 34-bis of the Consolidated Building Act (Testo unico dell’edilizia, D.P.R. 380/2001), they are not unlawful works and do not need a retroactive permit. They are declared.

This guide explains what construction tolerances are, the percentages set by the law, the difference between dimensional tolerances and execution tolerances, how construction tolerances are declared and when they are not enough. It is written by Federico Cappellina Architects, an architecture practice in Verona that follows the construction of its own projects, for foreign owners, buyers and investors who meet the subject in a purchase, a mortgage or a renovation. The reference text is Article 34-bis of D.P.R. 380/2001 (in Italian), in the version in force since 28 July 2024 after the “Salva casa” decree (Decree-Law 69/2024, converted into law 105/2024). The percentages and dates below refer to that text. This is not legal advice: every property has to be checked against its documents.

Construction tolerances in Italy in brief

Construction tolerances are not building violations: they are deviations within the limits set by law.
For measurements (height, distances, volume, covered area) the general limit is 2 per cent of the measures stated in the building title.
For works completed by 24 May 2024 the limits rise, depending on the useful floor area, up to 6 per cent.
Execution tolerances cover geometric irregularities, finishes and the position of internal services and works.
Construction tolerances are declared through the statement of a qualified technician, or in a declaration attached to the deed of transfer.
Protected buildings have narrower limits.

Construction tolerances in Italy: CD Home in Verona, a single-storey villa with a glazed facade at dusk, designed by the studio — CD Home, Verona: a project by the studio, shown as a reference of language, not an example of how construction tolerances apply to a given building.

What construction tolerances are and what they are for

No building site reproduces the drawing to the millimetre. Walls have real thicknesses, floors settle, and prefabricated elements have their own manufacturing tolerances. The law recognises this with a simple rule: a small deviation from the building title is not an unlawful work. The purpose is to avoid that every difference of a few centimetres prevents a sale or a mortgage. For a foreign buyer this is the practical point: a deviation within the construction tolerances should not, by itself, stand in the way of the transfer, provided it has been properly declared.

But a tolerance is not a permit. It does not authorise anyone to build differently from the title, and it does not apply if the limits are exceeded or if it hides a substantial change. Construction tolerances fall into two categories, both in Article 34-bis: dimensional tolerances (paragraphs 1 and 1-bis) and execution tolerances (paragraphs 2 and 2-bis). They are different from the retroactive regularisation of works, which is covered in our guide to regularising building works in Italy (sanatoria edilizia).

The “title” here is the building title (titolo abilitativo) that authorised the works, which may be a building permit, a SCIA or another title. Construction tolerances are always measured against that document, which is why the first step in any check is to retrieve it. If you are unsure which titles exist for a house, read our guides to the building permit in Italy and to CILA and SCIA.

Dimensional construction tolerances: the percentage limits

Paragraph 1 of Article 34-bis provides that a failure to respect height, distances, volume, covered area and any other parameter of the individual property units is not a building violation if it stays within 2 per cent of the measures stated in the building title. This is the general rule for construction tolerances, and it is the one that applies to works carried out after the cut-off date mentioned below.

For works completed by 24 May 2024, paragraph 1-bis sets higher limits, depending on the useful floor area of the property unit:

useful area above 500 square metres: 2 per cent;
from 300 to 500 square metres: 3 per cent;
from 100 to 300 square metres: 4 per cent;
below 100 square metres: 5 per cent;
below 60 square metres: 6 per cent.

Paragraph 1-ter specifies that the useful area is calculated by considering only the area authorised by the title that permitted the works, net of any later subdivisions. A large villa therefore has a lower percentage tolerance than a small apartment, because the same percentage would produce a larger absolute deviation. The date of 24 May 2024 matters: for works completed later, the general limit of 2 per cent applies.

Two practical readings follow. First, the percentage is applied to each measure stated in the title, so the technician compares the finished building with the documents, parameter by parameter. Second, the limits depend on the useful area of the unit as authorised, not on the area as it may have changed since. Both points should be checked by the technician who signs the declaration, not assumed by the owner or the buyer.

Execution construction tolerances: finishes, geometry and internal services

Paragraph 2 treats as execution tolerances, and therefore not as violations, the geometric irregularities and the changes to finishes of the buildings that are of minimal extent, as well as the different location of services and internal works, carried out during the works for which the title was issued, provided that they do not breach town-planning and building rules and do not prejudice the habitability of the property.

For works completed by 24 May 2024, paragraph 2-bis adds, among others: a smaller dimension of the building, the non-realisation of non-structural architectural elements, irregularities in the masonry, a different position of internal openings, differences in ordinary maintenance works, the correction of design errors during the works and material errors of graphic representation in the drawings.

The difference from dimensional tolerances is one of nature: here the question is not a percentage but the minimal and non-substantial character of the deviation. An interior window moved or a partition off by a few centimetres falls within the execution tolerances; a new room or a change to an elevation does not. For the dimensional side, a technician measures; for the execution side, a technician judges, and that judgement is the reason a declaration exists.

Construction tolerances and finishes: timber terrace with lounge at SD Home in Soave, designed by the studio — SD Home, Soave (Verona): a terrace by the studio, shown as a reference of language, not an example of an execution tolerance.

How construction tolerances are declared

Execution tolerances realised during earlier works do not constitute violations and are declared by a qualified technician in the forms for new applications, communications and notices, at the time of attesting the lawful state of the property (paragraph 3). The lawful state (stato legittimo) is, in simple terms, the state of the property as documented by its titles and recognised as lawful. Alternatively, the declaration can be made in a substitute declaration attached to the deeds of transfer, or of creation and dissolution of rights over the property. In practice:

for a new application (CILA, SCIA, building permit) the technician declares the construction tolerances and attests the lawful state;
for a sale the declaration can be attached to the deed.

If the property is in a seismic zone, the technician also attests compliance with the seismic rules (paragraph 3-bis), attaching the authorisation or the proof that the term for the check has elapsed; for minor or non-significant differences a declaration on the lapse of the term is used. The rules on titles and on legitimacy are in our guides on CILA and SCIA and on the building permit in Italy.

For a foreign party, two practical consequences. The declaration is a technical document in Italian, signed by a professional who answers for it, so ask for a copy and for the technician’s contact. And the sale in Italy is completed by a notarial deed, so it is in the preparation of the deed that the documents are normally collected; it is good practice to raise the question of tolerances with your adviser early, not on the day of the signing.

Protected buildings: narrower limits for construction tolerances

The execution tolerances of paragraph 2 apply only to properties that are not under protection under the Code of cultural heritage and landscape. On a protected property, even a small deviation has to be read in the light of the landscape authorisation that governed the works. Paragraph 3-ter adds that the application of the article cannot limit the rights of third parties: a neighbour can still assert a distance that was not respected. In other words, construction tolerances settle the position of the property towards the building authorities; they do not settle the relationship with the neighbours.

When construction tolerances are not enough

the deviation exceeds the percentage limits;
the nature of the work has changed (a new volume, a new unit, a change to an elevation or to the outline of the building);
the work breaches town-planning or building rules;
it prejudices habitability;
it concerns a protected property, for the execution tolerances.

In these cases the way forward is regularisation: a sanatoria edilizia by way of the procedure called accertamento di conformità (verification of compliance), where the requirements are met. It is the subject of our guide to regularising building works in Italy. Declaring as a construction tolerance something that is not one can turn into an untrue declaration, for which the technician answers; it is a risk that falls on the professional and, indirectly, on the party who relied on the declaration.

Worked examples of construction tolerances

The examples are indicative; the assessment belongs to the technician on the specific case.

Interior height of 2.70 metres designed, 2.72 metres built: the deviation is below 1 per cent, so within the general limit of 2 per cent for construction tolerances, if the other conditions are met. For comparison, 2 per cent of 2.70 metres is 5.4 centimetres.
An interior wall two centimetres thicker: an irregularity in the masonry of minimal extent, an execution tolerance, provided it does not change areas or the ratio of window area to floor area beyond the limits.
An interior window moved: position of internal openings, an execution tolerance for works completed by 24 May 2024.
A porch closed with a fixed glass screen: not a tolerance, because it creates a volume or an enclosed space; it is assessed as a work to be regularised.
A distance from the boundary smaller than required: even if the difference is small, it may breach the minimum distance; the percentage tolerance applies to the measures of the title and does not remove the rights of third parties.

Construction tolerances and the design: how to prevent problems

The best prevention is a controlled site. Site supervision checks the setting-out before the masonry is built, measures heights while the floors are made, records variations and verifies that changes are authorised before they are executed. At the end of the works a survey of the finished building and its comparison with the design produce the “as built” drawings, which are needed for the certificate of habitability and for future sales. This is part of the work described in our guide to the house design process in Italy and, for the closing documents, in the certificate of habitability in Italy.

The same logic applies to the specification. A good construction specification states which tolerances the contractor must meet for each element, so that the legal tolerances are not the only yardstick on site. And the bill of quantities should be based on measured quantities, so that a difference between the drawn and the built quantity is visible early.

Construction tolerances in a facade detail: perforated screen on SD Home in Soave at night, designed by the studio — SD Home, Soave (Verona): a facade detail by the studio, shown as a reference of language, not an example of a tolerance limit.

Buying or renovating a house in Italy: construction tolerances in practice

If you are buying, ask your adviser to compare the building titles with the state of the property, and to tell you whether any deviations found fall within the construction tolerances or need regularisation. If you are renovating, the technician who prepares the application will attest the lawful state, which is the moment at which tolerances found in the earlier works are declared. In both cases the question is the same: is the deviation within the numbers of Article 34-bis, and is it documented?

For land and buildings that are still to be purchased, the checks that come first are listed in buying land in Italy; for a renovation, the cost side is in the cost of renovating a house in Italy. Where a property cannot be brought within the tolerances, the same budget should include the cost of regularisation, which we do not estimate here because it depends on the case.

How the Italian approach to construction tolerances differs from what you may know

In Italy the limits are written in the law itself, as percentages in the Consolidated Building Act, and the declaration is made by a technician in specific documents. In other countries small deviations are often handled in different ways, for example through inspection at completion or through minor amendments to an approved scheme. We make only this general remark and do not describe foreign rules: if you hold property elsewhere, do not assume that the same concept works the same way in Italy. What counts is the text of Article 34-bis, in the version in force since 28 July 2024, and the documents of the specific property.

Mistakes to avoid with construction tolerances

Treating a tolerance as a permit: it is not an authorisation to build differently, only the recognition that a minimal deviation is not a violation.
Applying the wrong date: the higher limits of 3 to 6 per cent are for works completed by 24 May 2024; for later works the limit is 2 per cent.
Using the current area instead of the authorised one: the useful area is taken from the title, net of later subdivisions.
Forgetting protected buildings: the execution tolerances of paragraph 2 do not apply to them.
Forgetting the neighbours: the rights of third parties are not affected.
Not declaring: a deviation within the construction tolerances is lawful, but it still has to be declared in the documents where the law requires it.

Italian terms at a glance

Tolleranze costruttive: construction tolerances, the subject of Article 34-bis.
Titolo abilitativo: the building title that authorised the works (permit, SCIA or other).
Stato legittimo: the lawful state of a property, as documented by its titles.
Superficie utile: useful floor area, the basis for the percentage limits of paragraph 1-bis.
Accertamento di conformità: the verification of compliance used for the sanatoria edilizia.
Tecnico abilitato: a qualified technician, such as an architect, an engineer or a surveyor, who signs the declaration.
Atto di trasferimento: the deed of transfer, to which a substitute declaration can be attached.

Construction tolerances in Italy: frequently asked questions

What are construction tolerances in Italy?

Minimal deviations between the building title and what was built that Article 34-bis of D.P.R. 380/2001 does not treat as building violations.

What is the limit of construction tolerances?

2 per cent of the measures of the title for height, distances, volume, covered area and other parameters. For works completed by 24 May 2024 the limits rise, depending on useful area, from 3 to 6 per cent (paragraph 1-bis).

What is the difference between dimensional and execution construction tolerances?

The first are percentage limits on the measures of the title; the second concern irregularities in geometry, finishes and the position of internal services and works that are of minimal extent and do not prejudice habitability.

How are construction tolerances declared?

By the statement of a qualified technician in the applications where the lawful state is attested, or by a substitute declaration attached to the deeds of transfer.

Do construction tolerances apply to protected buildings?

The execution tolerances of paragraph 2 apply only to properties not protected under the Code of cultural heritage and landscape.

Do construction tolerances remove the rights of neighbours?

No: paragraph 3-ter states that the application of the article cannot limit the rights of third parties.

What if a deviation exceeds the construction tolerances?

The regularisation by way of the verification of compliance should be assessed, if the requirements are met; otherwise the sanctions of the Consolidated Building Act apply.