Available space is key in determining a stair's shape. Straight stairs are the easiest and most affordable type to build. But because stairs with a landing—L-shaped or U-shaped stairs—are safer and easier to climb, they're often preferred where space allows. Circular stairs take the least space but are also the hardest to climb; in fact, rooms served by a circular stair often also have a primary stair for easier access with furniture and the like.

Stairs may be spiral, straight, circular, or any of several other shapes. And, of course, they may be wide or narrow, steep or gradual. As a general rule, the wider the stair and more subtle the climb, the more inviting the staircase—and the more floor space it will consume.

Here's a closer look at the major types of stairs:

A straight stair stretches from lower to upper level in one straight run. Though this is the easiest type of stair to build, it can be difficult to squeeze into a floor plan.

A return stair divides the run, reversing direction a full 180 degrees at a landing.

A circular stair generally sweeps in a broad curve from one level to another.

An "L" stair makes a 90-degree turn at a landing.

A winder serves like an "L" stair but requires less space (and is less safe to use) because the landing is divided into pie-shaped steps.

A spiral stair twists around a center pole in one of two ways. The common spiral stair has a straight center pole with steps radiating out from it; a helix-style spiral has a curving center support that follows the sweeping twist of the stair.