HELP!!! need help with a spiral stair case!!!! :(?

Question

hey i suck at this. i really do. ive never understood it so if someone can help. im designing a gallery for my design project. my total rise to the next floor is 15 feet. i need to know like exactly how far apart to put each piece and the tread. ....HELP! i know it sounds like im an idiot but im not! ive just never done this before please help as soon as possible. it would be greatly appreciated

Answer 1

While this is from an old copy (1985 !) of the Uniform building code, it might be of some help
Spiral stairways are required to have a clear walking area a minimum of 26" form the supporting column to the inner edge of the handrail. A run of at least 7.5" shall be provided at a point 12" from the the narrowest end of the tread, a minimum of 6'6" headroom must be provided and the rise shall not exceed 9.5"
Since this if from an old book, you'll want to avoid the extremes. e.g. keep the run more than 7.5" and the rise less than 9.5"

Maintaining a reasonable run at a point 12" from the narrowest part of the tread can be tricky, if the tread is triangular it restricts the angle you can use, but if the tread is trapezoidal you have more options. To have trapezoidal treads you can either have a large central column or an open center.
Since the stair is a "spiral" (actually a helix) you have to be careful with headroom. for example if the rise was 7.1" , to get 6'6" (78") headroom, you would need 11 risers in 360° but remember it was an old code book, I might try for 7' (84") especially since I a 6'4" tall, but while a 7" riser might be fairly reasonable for a straight stair (though it is a bit high) it is fairly low for a spiral. So if we stay with 11 risers per 360° we have a riser of 7-5/8" but that doesn't work for your 180" (15') total rise, so lets try 24@7.5", that means we need (to get 84" headroom) 11.,2 treads per 360° or each tread has an angle of 32.15° Opening or CAD program we quickly find a problem, for an angle of 32.25° the width at 12" from the apex is only about 6.9", however if we trim the point off to make a trapezoid 3" wide at the narrowest point, we can have a 10" tread 12" from the apex. the apex of the trapezoid will be about 5-3/8" from the center of the stair, so a solid center column about 11" in diameter should work well., Since the 26" minimum width is from an old book, lets try, say, 33" which will leave some room for a hand rail, since the the narrow end of the tread is 5-3/8" from the center, adding 33" gives us an outer radius of 38-3/8 and diameter of 76-3/4", 24 risers, 23 treads and 2.14 turns in the spiral.
Of course if you'd like a different rise and/or run you can recalculate.

Answer 2

Depends on building code where you are. If you google stair contractors (there are specialists) and call them up (explaining it is for a school project) they can explain the local code- then it is easy. For example if you need 9 inch rise and 10 inch tread, then you need 1 1/3 steps per foot (20 total) and the stairway will be 20*10 or 200 inches long (16 feet 8 inches). But that's just an example.

Answer 3

Using 6" rise and 9" run (This was considered standard.), You will need 15*2 = 30 treads. With a spiral staircase the 9" run should be about 20" short of the outer radius of the stair.

Answer 4

Well, I understand the ideal ratio for stairs is 11" run by 7"rise. So, the ideal place to make that ratio seems to be midway between the inside pole and the outside rail. Therefore, it's imperative to know the width (diameter) of the stairs.
15' multiplied with 12" equals 180". 180" divided by 7" equals 25 steps with 5" left over. Divide that 5" into the 25 steps and you get 2 tenths of an inch added to each step. So 25 steps measuring 11" run by 7 and 2/10 inch rise should get you to the next floor.
I hope you followed that.