Replies

1. 
   Jim_K_ | Dec 10, 2000 03:03am | #1

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   http://www.stairwaysinc.com, among other places, has all the charts in their brochure and last I looked on their web site. And they do great work, too. A 20', 1100 lb 2-story stair was within 1/8" of all my measurements. See if you have other questions after reviewing the charts.

1. 
   Stan_Foster | Dec 10, 2000 04:10pm | #2

   *Bulldog: Your 90 inch floor to floor height limits the turn to less than 360 degrees. This is to allow for comfortable headroom clearance. I would suggest a ten treads at 27 degrees a tread. This would swing 270 degrees. With 11 rises of slightly over 8.3 inches, this would be comfortable. The problem area is getting enough headroom under your landing as you are descending the stairs and stepping from the second tread to the first. You want to be under the landing with no tendency to duck. The part of the landing that you are trying to clear can also be concave radiused to provide more clearance also. I would be more than happy to send you a drawing of how I would build it. I however am a lot more experienced at building curved stairs than I am at sending drawings out of my computer. Hope this helps.

1. 
   Gabe_Martel | Dec 10, 2000 05:26pm | #3

   *I agree with Stan that your height of 90" does not allow for a standard spiral. I would increase the number of risers to 12 and this would decrease the height to 7.5 inches for each rise. It has an adverse effect on the tread depth but I find it easier to walk up. Why is the ceiling so low in this house?Gabe

1. 
   Jim_K_ | Dec 10, 2000 06:33pm | #4

   *And then there are the code considerations. 6'6" on headroom and treads that are 7.5+" deep at 12" from narrow edge. I don't think a 22.5° tread can do this, if code is applicable in this situation. A lot depends on where Bulldog's landing and stair entry need to be.

1. 
   Gabe_Martel | Dec 10, 2000 06:43pm | #5

   *How about a combination of spiral and conventional.Start with spiral for the first 180 and switch to conventional for the remainder.This would allow for both code and headroom and you would only have to sacrifice an additional 3 by 4 area of the second floor.Gabe

2. 
   Jim_K_ | Dec 10, 2000 08:06pm | #6

   *>I'm not familiar with the 12"offsetCABO "314.5 Spiral stairs. ...minimum width shall be 26 inches with each tread having a 7 1/2 inch minimum tread width at 12 inches from the narrow edge."My inspector cared and measured. He was even gonna hold me to a 6'8" height (I was borderline depending on how taut you held the tape) until gently reminded that CABO required only 6'6" on spirals vs the 6'8" on other stairs.Following the dimension chart at http://www.stairwaysinc.com/design.htm, and subtracting the one inch overlap of treads, it seems that he'd need 30° treads on 72 inches to meet code. I did the 76 inch stairs and needed 30° be/c the 27° missed by 1/8" (again, considering the approx 1" overlap of treads).

3. 
   Jim_K_ | Dec 10, 2000 09:17pm | #7

   *>Well here in the U.S....I'm in North Carolina--it was SC that tried to secede from the US, and not NC :) --and CABO (Council of American Building Officials), if I read the book right, combines BOCA, UBC, and the Standard Building Code. It has a separate section for winders, which is what the graphic seems to discuss. That section (314.4) of CABO, FWIW, requires 9" tread at 12" from narrow edge. CABO has an additional section for _spirals_ as different from _winders_ and as different from _circular_ stairways.I'm still curious where Bulldog's landings are. Pick the wrong degrees of curve regardless of code model and he might exit straight into a wall!

4. 
   LocalBulldog_ | Dec 10, 2000 11:43pm | #8

   *Thanks for all the help. This stairway is in a 2 story sauna type room where headheight will not be a factor except as it relates to the catwalk which you will access the stair from

5. 
   Jim_Walters | Dec 11, 2000 12:52pm | #9

   *I have never been good with all the math, but I just make a circle on the floor and figure the whole thing (rise and run) flat. Find the starting point and the ending point, adjust the treads until you get it right on your pattern, then build the stairs. Thats how the dummies do it.

6. 
   Stan_Foster | Dec 11, 2000 01:05pm | #10

   *Bulldog: I failed to mention that the parameters I suggested fall under our secondary stair code and obviously would not satisfy primary stair code. Gabe has a good point for going one more tread, but I preferably would have a higher riser with one less tread giving me more run which is definately in short supply. Fortunately you have a 6 ft. diameter stair to help this out. I have seen this same scenerio with stairs as narrow as 4 ft. I personally won't build any thing less than 5 ft. with 27 degrees of arc per tread. Again, this is considered a secondary stairs under our code.Your situation with only 90.5 inches of headroom requires you to descend as quickly as practical to get away from that landing. If the landing is square and the stairs turns 270 degrees, that places the nosing of the first tread right under the landing. With allowance for landing thickness and first tread height, this gives you over 81 inches of headroom. This is plenty, however when you are descending the stairs going from the second tread to the first tread, the bottom of the upper landing is 73 inches +/-. With a 27 degree clearance you would have more horizontal clearance that is very much felt when you are passing under the landing. I feel that by sacrificing one tread and increasing the rise a little, that the extra run and horizontal headroom gain is the least of two evils. Hope this helps.

2. 
   LocalBulldog_ | Dec 11, 2000 01:05pm | #11

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   I need to calculate the approximate turn of a spiral stair. Finish floor to finish floor is 90 1/2 inches. The stair will be 6 ft diameter. Does anyone know how to figure out where the stair will terminate? 90 degrees? 180 degrees? Any help would be greatly appreciated.