condos are on the 2nd floor or 1st floor.
Alot of homes in my area are built above street level, some more than others. We are close to being below sea level (new orleans the city next to us is actually below sea level) so alot of our homes are built up on higher ground, on stilts or columns, etc so that they do not flood during heavy rain storms or hurricane season.
In general though, houses are built on their own. As in, not attatched to another building or another persons home and its also cheaper to build at street level rather than building up the land or raising the house on columns. Its also just unneccasary in places that arent prone to flooding.
uhm what? Condos are basically apartments privately owned, which means they start on ground levels and go up. Houses that have other houses on top of them would be apartments. It's like asking why zebras have stripes and horses dont. Well because they're two different things...