Zero-lot lines are a zoning designation that allows developers and builders to make as much use of a lot as possible. They're used when residential lots command premium prices as a way to provide more usable yard space and reduce the selling price of the home. Instead of having side-yard setbacks on each side of the home, zero-lot line homes have one side that rests on or close to the lot line. Depending on zoning requirements for side-yard setbacks, it can double the side-yard space. Most of the time, zero-lot line homes are two-story to increase the square footage of these homes. These homes may also be called patio homes, garden homes, condos or townhomes, depending on how the builder markets the project. Although these homes provide more livable outdoor space, one of the downsides to zero-lot lines is that window placement may be limited to just three sides of the home.