Diameter can be defined as a straight line going through the center of a circle connecting two points on the circumference. In other words, when we ask you what diameter you would like for your stair what we are really asking is, “How wide do you want your spiral stair to be?”
At Salter, the smallest stair diameter we offer is 3 feet 6 inches which translates to a 42” x 42” diameter. If you are going through a hole in the floor your finished floor opening should be two inches greater than your stair’s diameter. For example, if you are using a 3’6” spiral stair to get you access to an attic through a hole in the floor then you would need a finished floor opening of 44 inches x 44 inches. The extra two inches ensure that you fingers will travel freely and unhindered as you walk up the spiral stair. Matching the floor opening to the exact measurement of your stair’s diameter would cause your fingers to pinch while using the handrail. For more information on finished well opening sizes please refer to question #1.
While going through a hole in the floor is a common application for spiral stairs, many of our customers install a loft stair kit at the face of a loft or deck. If that is the case you will want to think about two things: your desired clear walking space and whether or not you want to meet building code.
When we talk about “clear walking space,” we are focusing on the physical area you have to walk up and down the stairs. One of the major benefits of a spiral staircase is the large surface of each step in a small space. This amount of clear walking space is determined by your stair’s diameter. Starting at a 3’6” diameter, your clear walking space will increase by 3” for every 6” of additional diameter.
Clear Walking Space Guide Stair Diameter Clear Walk Space 3′ 6″ 17″ 4′ 0″ 20″ 4′ 6″ 23″ 5′ 0″ 26″ 5′ 6″ 29″ 6′ 0″ 32″
It can be hard to envision these measurements without physically seeing them. A quick trick to seeing your clear walking space is to use a sliding door in your home. Slide open your door to match the clear walking space for your diameter. For instance, if you choose a 3’6” diameter, open your door exactly 17”. This 17” represents the clear walking space you would get with our smallest 3’6” stair. Use the chart above as a guide to determine what the most comfortable walking space is for you and your guests. This can help you narrow down your diameter measurements if you’re having difficulty.
Your measurements may be defined by your staircase’s surroundings. If you need a smaller stair with a 3’6” or 4’ diameter, you will have a smaller clear walking space, but it is still complete safe to use. This is because the structure integrity of our stairs does not change with diameter size. We stand behind our build and offer a lifetime warranty on all welding and fabrication.
If you have a larger amount of space for your spiral staircase, you can choose to install a larger stair that will provide a more clear walking space. Generally speaking, a stair with a diameter of 5′ or larger is going to be very comfortable for your application.
Spiral stair building code requires your stair to have at least a 5’ diameter. Our 5’, 5’6” and 6’ code package stairs will meet code in many states across the nation. Now that you know a little more about spiral stair diameters, check out our building code page to learn more about code requirements of your spiral stair.
If you have any additional questions about your stair’s diameter or building code, call one of our consultative designers for instant answers!
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