Why do Taiwan door plates often have 「之1」?

Question

Weirdo · Accepted Answer

It's an annex number, not a floor. Roads reserve a sequential plate every few metres. When those run out — a building changes, or a new house is squeezed into the gap — household registration hangs the extra plate off the neighboring base number as 之1.

Taipei City’s Road Naming and House Numbering Ordinance, Article 9, is practical: reserve one plate every six metres along the road. After numbering, if a building changes or a new house is built in a reserved gap, the extra plate is a 支號 — a branch number of the adjacent building. Taichung’s ordinance is blunter: reserve a number every four to six metres; if that is not enough, number it as the neighbor’s 附號, written 「○之○號」. A floor with its own door stays a floor (○號○樓); another household on the same floor becomes ○號○樓之○. Taipei says 支號, Taichung says 附號. House numbering is local autonomy. The logic is the same: when the integers run out, hang the extra household off the neighbor.

New Taipei’s Civil Affairs Department said this out loud in 2020: before 20 October 1999 (民國 88 年 10 月 20 日), some apartments used 之1號 and 之2號 for the 2nd and 3rd floors. That collided with the later annex form 2之1號, which is a ground-floor extra. The rewrite turned those floor-as-之 plates into ○號○樓. On a current plate, 「之1」 is usually a household, not a storey. On an old one, ask which system you are looking at.

Why do Taiwan door plates often have 「之1」?

Numbers are reserved along the road

Some old 「之1」 plates meant a floor