[robertnealan]

Zoning restrictions are far more restrictive in the United States than in a city like Tokyo, where the government has largely only enacted laws preventing specific cases that would be considered very harmful (opening a heavy industrial businesses in a residential neighborhood for instance).

In most of the US most land in smaller cities are zoned for single family housing only. This often means you can only build a house for one family (no duplexes) with arbitrary restrictions on a variety of other things (minimum lot sizes, maximum house sizes relative to lot size, required setbacks from property lines to the house, etc).

In the event you are able to build a du/triplex it's rare you'd be able to convert any part of it for business use unless the land was already zoned for multi-use, where they allow mixing of residential and commercial uses.