Learn Italian: È fondamentale che nessuno evacui la casa da solo. - It is essential that nobody evacuates the house alone.

The sentence starts with È fondamentale che (It is essential that). This is an impersonal expression showing strong necessity, which is a classic trigger for the subjunctive mood in the clause that follows.

Evacuare is an -are verb. Why does its subjunctive form evacui end in an -i?

In the present subjunctive, regular -are verbs change their ending to -i for all three singular persons (io, tu, and lui/lei). Since the subject here is nessuno (which is treated as a third-person singular), we use evacui. For comparison, the normal present indicative form would be evacua.

Doesn't Italian usually require a double negative with nessuno, like "non evacui nessuno"?

You only need the extra non when nessuno comes after the verb. Because nessuno is placed before the verb as the subject in this sentence, the non is dropped.

Why use da solo instead of just solo for "alone"?