Il libretto di impianto resta valido a condizione che sia completo.

Libretto di impianto is a technical expression. In everyday translation, it usually means something like system booklet, installation record, or plant/system logbook, depending on the context.

• libretto = booklet, small manual, record booklet
• impianto = system, installation, plant

In technical or legal Italian, this often refers to an official document connected with a heating system, installation, or similar equipment.

Italian usually uses the definite article more often than English.

So Il libretto means the booklet:

• il = the
• libretto = booklet

In English, you might sometimes drop the article depending on context, but in Italian it is normal and often necessary to include it.

Resta valido means remains valid or stays valid.

• resta comes from restare = to remain, to stay
• valido = valid

So the idea is that the booklet continues to be valid, but only under a certain condition.

You could also find rimane valido in Italian. Resta valido and rimane valido are very similar here.

A condizione che means provided that, on condition that, or as long as.

It introduces a condition that must be met.

So:

• a condizione che sia completo = provided that it is complete

This is a fairly formal and common expression in written Italian, especially in official, legal, or administrative language.

Because a condizione che requires the subjunctive in Italian.

• è = indicative
• sia = subjunctive of essere

So after expressions like a condizione che, Italian normally uses the subjunctive because the statement refers to a condition rather than a simple fact.

Examples:

• È completo = It is complete.
• A condizione che sia completo = Provided that it be / is complete.

For an English speaker, this is important because English often does not show this difference clearly, but Italian does.

Sia is the present subjunctive of essere for:

• io
• lui / lei
• Lei (formal you)

In this sentence, it refers to il libretto, which is singular, so it means that it be / that it is.

Here is the present subjunctive of essere:

• che io sia
• che tu sia
• che lui/lei sia
• che noi siamo
• che voi siate
• che loro siano

Because completo agrees with il libretto, which is:

• masculine
• singular

So the adjective must also be masculine singular:

• il libretto ... completo
• la documentazione ... completa
• i libretti ... completi
• le schede ... complete

Even though completo appears after sia, it still describes il libretto.

Di impianto specifies what kind of booklet it is.

Italian often uses noun + di + noun where English might use:

• a compound noun
• an adjective
• a prepositional phrase

So:

• libretto di impianto = booklet of the system/installation
• more naturally in English: system booklet or installation booklet

This structure is extremely common in Italian:

• libro di cucina = cookbook
• scarpe da tennis = tennis shoes
• centro di assistenza = service center

This is a natural and formal Italian word order.

The structure is:

• Il libretto di impianto = subject
• resta valido = verb + complement
• a condizione che sia completo = conditional clause

Italian often places the main statement first and then adds the condition after it.

A more literal breakdown is:

• The system booklet remains valid
• on condition that it is complete

This order sounds very normal in official Italian.

Yes, se è completo would be grammatically possible, but it is not exactly the same in tone.

Compare:

• resta valido se è completo = it remains valid if it is complete
• resta valido a condizione che sia completo = it remains valid provided that it is complete

The version with a condizione che is more formal, precise, and typical of bureaucratic or legal language.

Yes, definitely. It sounds formal, administrative, and technical.

Clues:

• libretto di impianto is specialized vocabulary
• resta valido is formal wording
• a condizione che is a formal connector
• the subjunctive sia is typical of careful written Italian

A more everyday way of expressing a similar idea might be less formal, but this sentence is exactly the kind of phrasing you would expect in regulations, manuals, or official documents.