Girl Scouts of Southeastern Pennsylvania settled on a one-story facility with a surprisingly smaller footprint than initially anticipated with a two-story design.(Architect: Greenfield Architects, Lancaster, PA; Builder: High Construction, Lancaster, PA)

Figuring out how many stories your building should have isn't always easy-or obvious.

"Initially, some clients have definite ideas about wanting a one-story or a two-story building," says Frank Fox, RA, AIA, of Greenfield Architects in Lancaster, PA. "We analyze all their needs, as well as the site. The whole package will point us in the right direction for the height decision."

Sharon Smith, CEO of Girl Scouts of Southeastern Pennsylvania, went through the process with the organization's recently completed headquarters building located on the border of Montgomery County and the City of Philadelphia. "We had a partially wooded site and wanted to have the smallest possible footprint," Smith explains. "Although we assumed a two-story building was the answer, there were many more things to consider."

Lots of things to consider, in fact. Most of the time, unless land costs are extremely high, the same usable square footage can be constructed less expensively on one floor rather than two or more.

Drawbacks to multi-story buildings: They have to support "floor loads" that are higher than roof loads; they're subject to more stringent fire code requirements; the wall systems are generally more expensive; and, of course, they have to be equipped with stairs, elevators, and vertical utility shafts. You actually have to construct a larger building to get the same usable square footage.

The Girl Scouts enjoyed an outcome that was right on target. "Greenfield Architects did a wonderful job of setting us up with a practical, one-story building that had a central core and two wings, while still giving us a smaller footprint than we initially [thought we would need]," Smith said.

The question of one story versus two often comes up in the context of building office space as part of a larger industrial facility. Single-story office space within the "main box" of the facility usually is the least expensive option, but if a lot of office space is required, you may want to think about using a mezzanine to stack the office space, still within the main box. This requires the cost of adding stairs and an elevator, but it still costs less than building an addition to the main facility. However, building an addition for office space can make sense if you need to keep the main box of the facility totally dedicated to industrial uses or if the office addition is suitable as the focal point of your design. It can also make sense if you need to separate "clean" and "dirty" areas to provide a more inviting area for customers and guests.

Alexine Cloonan, AIA, RLA, of Homsey Architects in Delaware, thinks building multiple stories can be a good choice in certain circumstances. "In an urban setting, land is at a premium," she points out. In such situations, "building two or more stories is cost effective." She adds an environmental concern: "One-story buildings usually generate more storm-water runoff, which both damages the environment and is costly to manage."

Adding another story later is always an option-but this works best if you plan for it when you build originally. If you expect to expand vertically later, include certain features, such as an elevator pit and space for elevators and stairs; a roof slab that can become a floor slab for the added story; mechanical systems that do not require rooftop equipment; and columns that extend through the roof so they're accessible. These features will increase the initial cost substantially, so be certain of your future needs before designing a vertically expandable structure.