Just a hunch but 1x1 buildings can typically grow up to x4 if there is room for the "yard" to be added. I'm guessing that the 1x1 version is just simply the building without any yard.

Same curiosity as Chrisser! Looks great though and will add some variety to the occasional 1x1 spots if it's truly 1x1..

Love it! However, in your screenshot it doesn't look like it's 1x1. Where does it get the extra space for the fountain and such?