Wooden Steps for a Spiral Staircase

Hardwood vs. Softwood

• Hardwood comes from trees with broad leaves such as oaks, birches and maples. Softwood treads are made from trees with needle-like leaves, including pines, spruces and cedars. As their names imply, hardwoods are denser than softwoods and more durable than their softwood counterparts. However, softwood treads are less expensive than hardwood treads. Both softwood and hardwood treads are graded for the beauty, density, moisture content and size. The cost of hardwood and softwood treads is based on the treads' grades.

Design

• All the treads of a spiral staircase connect to a pole that runs down the middle of the stairs. The end of the tread next to the pole is not as wide as the step's outside end. The vertical space between each tread is known as the rise and is occupied by what is called a riser. The rise between steps can be no more than 9 1/2 inches, according to the building code specifications provided by the Salter Spiral Stair website. Spiral staircase steps must have a width of at least 26 inches, making the staircase's diameter approximately 5 feet. The step's nose, or the part of the tread that extends beyond the riser, can be 1.25 to 1.5 inches long.

Maintenance

• Outdoor spiral staircases require more maintenance than indoor staircases since they deal with weather elements and exposure to sunlight. This maintenance for outdoor stairs includes finishing, or providing protection to wooden material. Clear film finishes and water-repellent preservatives are two common types of finishes. According to the Iowa State University website, hardwood treads require more finishing than softwood treads. Maintaining interior wooden treads consists of sanding rough edges, caulking holes and applying stain to beautify the treads.

Stair Codes

• The U.S. Uniform Building Code (UBC), Stairs-Residential Building Code (RBC) and International Residential Code (IRC) have regulations regarding how to build stairs, including spiral staircases. Each municipality also has its own specific codes for building stairs. Spiral staircases usually have a different set of standards from other types of staircases. For example, California spiral staircase treads must be at least 10 inches wide at their narrowest end. Other municipalities may have different requirements, but the minimum tread width for spiral stairs usually ranges between 9 and 12 inches.