The poorly positioned or absent apartment number remains one of the primary causes of NPAI mail in collective buildings in France. Writing a postal address with a reliable identification supplement requires precise formatting, framed by technical constraints that automated sorting services exploit line by line.
Address Supplement Line: Technical Constraints of Automated Sorting
Optical sorting machines read the address from bottom to top. The last line corresponds to the postal code and city, the second to last to the street number and name. The apartment number, floor, building, or stairwell should therefore not appear on the street line: they disrupt the automatic recognition of the street label.
The address supplement must appear on a dedicated line, distinct from the street line. In France, this line is placed above the street line, that is, in position 3 in the six-line scheme. The standard imposes a maximum of six lines and thirty-eight characters per line, without punctuation, with the last three lines in uppercase.
A compliant example for an apartment in a residence:
- Line 1 – Title, first name, last name of the recipient
- Line 2 – Apartment 12, stairwell B, 3rd floor (internal identification supplement for the building)
- Line 3 – Residence Les Tilleuls, building C (external identification supplement, if necessary)
- Line 4 – 15 RUE DES LILAS
- Line 5 – 75020 PARIS
- Line 6 – FRANCE (only for international shipments)
When the supplement is short, we recommend grouping the apartment and building on a single line to avoid wasting an additional line. Knowing how to write an apartment number in an address precisely avoids this type of line distribution error.
Abbreviations for Apartment Numbers: Accepted Usages and Common Pitfalls
The abbreviation “app.” (with a period) is the standardized form in French for “apartment.” The form “apt” without a period remains common but is more typical of North American usage. In French postal context, “app.” followed by the number without unnecessary space is the safest spelling.
For an office, the standardized abbreviation is “bur.” We regularly observe erroneous labels: “Appt,” “APT.,” “apart.,” or even the symbol “#” imported from Anglo-Saxon formats. These variants do not systematically cause rejection by sorting, but they complicate the work of the mail carrier during final delivery.
Case of the Number Alone without Mentioning “app.”
Some senders only write the number (“12”) without specifying that it is an apartment. This practice creates ambiguity with a building or stair number. Always specify the nature of the supplement (app., bât., esc.) before the number to eliminate any confusion.
Format Differences Between France, Canada, and the Netherlands
The positioning of the apartment number varies according to national postal conventions. This point is critical for international shipments.
In France, the supplement precedes the street line. In Canada, Canada Post recommends placing the apartment number on the same line as the civic address, separated by a hyphen: 12-350 rue des Érables. If the address exceeds the character limit, the unit number moves to the line above.
In the Netherlands, PostNL uses a distinct system: the postal code (four digits followed by two letters) combined with the house number is sufficient to identify a unique distribution point. The apartment number is added as a suffix to the house number, separated by a hyphen or a letter (e.g., “25-3” for the third floor of number 25).
| Country | Position of Apartment Number | Typical Format |
|---|---|---|
| France | Separate line above the street | App. 12, Bât. C |
| Canada | Same line as the street (prefixed) | 12-350 rue des Érables |
| Netherlands | Suffix of the house number | Keizersgracht 25-3 |
Address Writing Errors That Cause NPAI Returns
The acronym NPAI refers to mail returned for lack of addressing. In collective buildings, the absence of an address supplement is the primary cause of non-delivery. The mail carrier serving a building with several dozen mailboxes cannot guess the intended apartment if only the name and street are on the envelope.
Three recurring errors are:
- Apartment number placed after the postal code or at the end of the address, where automated sorting does not look for it
- Mixing the address supplement with the street label on the same line, making machine reading inconsistent (e.g., “15 RUE DES LILAS APP 12”)
- Exceeding thirty-eight characters on a line, which truncates the supplement when printing routing labels
Mailbox Labels and Address Consistency
The problem is not limited to the sender. If the label on the recipient’s mailbox does not match the name indicated on the envelope, the mail carrier may consider the mail as undeliverable. Consistency between the name on the envelope and the name displayed on the mailbox is a prerequisite often overlooked in condominiums.
A correctly structured address supplement, a standardized abbreviation, and an up-to-date mailbox label form a triptych. Neglecting any of these elements is enough to turn a standard shipment into returned mail, with the delays and costs this implies for both the sender and the recipient.
