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Old 07-14-2011, 01:26 PM   #1
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spiral deck stairs requirements


I was just wondering whether stairs like those illustrated in my attached diagram meet general code requirements for a deck. The stairs make a 1/4 turn, with the rise being 7.5" per step, and the run is 12" for the rectangular steps. The spiral guys have a run of about 6" on the inside edge and about 18" on the outside edge. Thanks.
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Old 07-14-2011, 02:02 PM   #2
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spiral deck stairs requirements


Sounds a little too tight for my neck of the woods, but your codes may allow it. Give the local official a call and ask about the minimum tread depth on residential spiral stair treads.

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Old 07-14-2011, 03:42 PM   #3
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Sounds a little too tight for my neck of the woods, but your codes may allow it. Give the local official a call and ask about the minimum tread depth on residential spiral stair treads.
The info I've found for spiral stairs online says that the minimum tread width is 7.5" at a distance of 12" from the "center column." I'm not sure if that applies to decks too, and I'm not sure what the "center column" would be in this case. If the center column is interpreted to be the inside edge, then these stairs would be at about 7.75" wide at 12" in from there, so they'd be OK.
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Old 07-14-2011, 03:45 PM   #4
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spiral deck stairs requirements


You measured correctly and you answered your question. Deck stairs fall under the same guidelines as interior stairs.
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Old 07-14-2011, 03:55 PM   #5
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You measured correctly and you answered your question. Deck stairs fall under the same guidelines as interior stairs.
OK, thanks. Is there any additional restrictions/requirements if these deck stairs also happen to be for the main entrance to the house?
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Old 07-14-2011, 04:02 PM   #6
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spiral deck stairs requirements


As long as they have all the pieces a normal interior stair would. Guardrails for stairs climbing over 30" in height. Handrail on at least one side. You covered the tread depth requirement. And the riser should be under 7-3/4" if you're under the 2003 IRC jurisdiction.
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Old 07-14-2011, 11:20 PM   #7
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spiral deck stairs requirements


The best I can remember the treads must be 10 1/2" at 15 inches from radius edge here in Tennessee.
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Old 07-15-2011, 08:38 AM   #8
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spiral deck stairs requirements


We put up a spiral staircase kit in our log home. The fact is, because this type of stairs is rarely used, most building inspectors aren't familiar with the codes pertaining to them. I suggest you find someplace that sells the kits and talk to them. Ours came from www.duvinage.com.
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Old 07-15-2011, 09:23 AM   #9
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The best I can remember the treads must be 10 1/2" at 15 inches from radius edge here in Tennessee.
I think I calculated it wrong before. It goes from 6" wide at the inside to 18" wide at the outside, over a length of 40". That is, it increases by 12" over a distance of 40". So, at 12" from the inside the width would be

6 + 12/40 * 12 = 9.6 inches

and at 15 inches from the inside, I get

6 + 15/40 * 12 = 10.5 inches.

So, it looks like it would hit the nail on the head in Tennessee.
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Old 07-15-2011, 09:36 AM   #10
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spiral deck stairs requirements


In the diagram above, that is a radius stairs not a spiral staircase. Code here calls for a spiral to be a secondary staircase with a standard staircase as the primary. A radius staircase can be the primary, if in code, but a spiral can not.
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Old 07-15-2011, 10:13 AM   #11
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spiral deck stairs requirements


The smart thing to do would be to show your drawings to the local code office to determine if it is acceptible. It could help avoiding a "tear-out" and rebuild.

A state or local code authority has the abilty to impose stricter local requirements than the model code. A code, like the IBC or IRC, is just a minimum standard and not necessarily the best way to do something.

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Old 07-15-2011, 11:06 AM   #12
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spiral deck stairs requirements


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In the diagram above, that is a radius stairs not a spiral staircase. Code here calls for a spiral to be a secondary staircase with a standard staircase as the primary. A radius staircase can be the primary, if in code, but a spiral can not.
Interesting. What code are you under? I had no issues at all with my spiral being primary. Actually, it's the only staircase in the house.
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Old 07-15-2011, 03:26 PM   #13
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spiral deck stairs requirements


I don't know what code Memphis and Shelby County Tennessee uses. I live in Chattanooga now and I don't think the code people here even know which code they use.

How do you get furniture up the stairs?

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