Standard incline stairways are the most common way of joining two floors in private homes but take up the most room. They measure at least 36 inches wide and up to 12 feet long between levels or landings. The International Residential Code, or IRC, which is the foundation for all U.S. state and municipal building regulations, defines standards for stairways. It specifies a minimum headroom of 6 feet, 8 inches as measured from the slope line joining the tread nosings, or from the floor surfaces of landings or platforms that are part of the stair. However, projections extending from floors under which the stair passes may extend into the required headroom height up to 4.75 inches.
Grand staircases fronting multistory entry halls can boast head heights limited only by the finances of the homeowner and the imagination of the designer. Interior stairways in 1,000-square-foot homes or urban lofts may need to squeeze into far smaller spaces, with limits on dimensions such as headroom that are imposed by building codes.
Spiral staircases take up far less room than standard ones, sometimes occupying as much as 50 percent less space. They, therefore, work for areas that have no room for inclined staircases. They must have a minimum headroom of 78 inches, beginning from the top of the stair step up to the bottom of the next stair step or landing. Dimensions not specifically mentioned in the section for spiral staircases must follow the definitions for standard stairways.
Bulkhead enclosure stairways provide access from an outside grade level such as a lawn, to a lower finished level such as a basement. These constructions can ignore headroom specifications if they meet all the following conditions: They must not be the only way to leave the lower space; the maximum height from the finished basement level to the upper grade level must be 8 feet or less; the opening from the grade level to the stair must be covered by at least one hinged door.
The Americans with Disabilities Act also bases its building codes on the IRC, but with modifications that enable the disabled to access stairs. ADA regulations are mandatory for commercial spaces such as hotels or gyms, but optional for private residences. However, they form useful guidelines for homeowners who are themselves disabled, or wish to sell their homes to that market. For example, the ADA requires two handrails for staircases, instead of just the one handrail specified by standard codes. In the case of headroom, the ADA follows the IRC code exactly, as this is sufficient to allow those with mobility, vision or hearing problems to negotiate stairs.
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