Why are the houses in Hanoi's Old Quarter so narrow?

The feature is especially visible in Hanoi's Old Quarter. Its streets historically grew as trade and craft streets: people lived and worked in their houses, with the shop or workshop right on the street. The rest of the space — storage and living quarters — extended deep into the plot, and the house could rise several floors.

The reason for the shape is tax. According to Vietnam's National Authority of Tourism, which the post cites, merchants were taxed according to the width of their house. So owners found it cheaper to keep the front narrow and build the house longer and deeper. These buildings are called nhà ống — literally "tube houses".

A clear example is the historic house at No. 87 Mã Mây Street: its front is only about 5 meters wide, but the building runs 28 meters deep. Inside were a shop, a storeroom, living quarters and a small courtyard for light and ventilation.

Over time narrow buildings became even more common: urban land grew scarcer, the population grew, and space had to be used as efficiently as possible. Narrow houses are still built today — the post gives a 5 × 20 meter plot as an example of a modern house in this tradition. So a three-meter-wide house you see in Vietnam may well be an echo of taxes that are several centuries old.