When building a house, the stairs deserve special attention. This is because the stairs need not only be sturdy enough to support your weight, but be built in such a manner that the treads are evenly spaced and the steps are not too steep. As might be expected, there are building codes for stairs, such as the International Residential Code, or IRC, the U.S. Department of Labor's Occupational Safety and Health Administration, or OSHA, and also those set forth by the town offices of city halls in your community. Spiral stairs, due to their complexity and spiral shape, also have certain building regulations associated with them in order to make them safe for you to negotiate.
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Width of Staircase
While the building codes for stairs recommend a specific width of 36 inches at the minimum, spiral staircases are allowed to be narrower. The minimum width for these staircases is 26 inches.
Width of the Tread
The tread is considered to be the flat portion of the staircase on which you place your foot. For a conventional staircase, the minimum depth allowed for the tread is 10 inches. Due to the spiral shape, the minimum depth of the tread can be 7 1/2 inches. However, this minimum depth must be reached within 12 inches of the narrowest point. In other words, since the tread of a spiral stair looks like a triangle, measure down 12 inches from the point of the triangle, then measure the depth of the tread. If the tread does not measure 7 1/2 inches, then the tread does not meet regulations.
Riser Height for Spiral Stairs
The riser, according to the Merriam-Webster Dictionary refers to "the upright member between two stair treads." The height of the riser refers to the distance you have to lift your foot to get from one tread to another. For conventional stairs, the minimum height allowed for the riser is 7 1/2 inches and the maximum is 9 1/2 inches. This does not change for the spiral staircase.
Handrail Regulations: Distance from Wall
Handrails must be taken into account when building spiral staircases. If the spiral staircase is built into curved walls, such as inside a tower or turret, the distance by which the handrails extend into the stairway must be considered for this can affect the overall width of the staircase. According to IRC, the maximum amount the handrails can extend away from the wall is 4 1/2 inches. Since the minimum width of the stairs is 26 inches, you need take into account the amount of room the handrails take up. If you have one handrail, the staircase must be 26 inches wide plus 4 1/2 inches for the handrails, which means you would need an overall stair width of 30 1/2 inches. If you have two handrails, the staircase must be 26 inches plus 9 inches for an overall stair width of 35 inches.
Handrail Regulations: Width and Height
For conventional staircases, if the overall rise of the staircase -- the height above the ground -- is 30 inches, the handrails must be 36 inches. If the overall rise is less than 30 inches, the handrails must be 34 inches tall. This is the same for spiral staircases. Whether the stairs are conventional or spiral, the graspable width of the handrail must have a diameter of 1 1/4 inches to 2 inches in diameter. The handrail itself must be able to support over two hundred pounds of force.
Headroom refers to the distance from the stair to the floor above in a stairwell. This means that when you walk up a set of stairs, you should be able to do so without striking your head on the ceiling as you go up or down the stairs. For conventional staircases, the headroom allowed is 6 feet 4 inches. With a spiral staircase, this is increased to 6 feet 6 inches.
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