The spiral stair height determines the number of treads your spiral stair will require. This is crucial to the spiral stair design.
The spiral stair height will be the distance from the finished floor below to the finished floor above. The double-headed arrow shows this in Figure 1.
You may have a rough idea of you floor height. But you should measure accurately, say to within + or – 1/8”. Because this will assure that the spiral stair will fit your home the best.
Figure 2 shows cross sections of typical floor parts, flooring layers, ceiling and framing. Builders install headers around the perimeter of the second floor stairwell. The single-headed arrows show non-builders exactly where to measure on each floor. We will discuss the dimension “A” later in this post.
You could get the measurement off the building plans for new home construction. Or, your contractor should be able to tell you. But beware that this height may still change. For instance, it could change if the home is not built exactly to the plans. This is not an uncommon occurrence. Or, you might inadvertently affect the height when you decide on different finished flooring.
You will make the surest measurement once you have floor framing installed.
How to measure spiral stair height
If you are remodeling an existing home, measure the spiral stair height as directly as possible. If you have not yet cut out the stairwell, you can measure the height in at least three ways.
First, you could simply measure the floor height directly at another stairwell in your home. But, just be sure that your floors are level. Because if the floors are not level, the spiral stair height could change depending where you measured it.
Second, you can use the thickness of your top floor system to determine the stair height. Add the combined thicknesses of the ceiling, floor joists or headers, subfloor and finished flooring. See dimension “A” in Figure 2. However, use this method only if you are sure of your floor joist height. Because joist dimensions can change over time.
Next, measure from the bottom floor to the ceiling above. Add this to the top floor system thickness, and you have your spiral stair height.
Third, you could measure the height through a hole through the top floor layers and ceiling in the area where the stairwell will be cut out. Drill a hole only large enough to allow a tape measure to slip through. Now you can measure the floor height directly. You will remove the damage when you cut out the stairwell.
Carpet finished floors will add no appreciable thickness unless the carpet has an unusually thick pile. Speak to your spiral stair designers if you plan to tile the bottom floor, or install the spiral on concrete. Because options are available for either installation.