Stair Question

I put the technical data at the end of this email. I'll give you the Blah, Blah, Blah first.
I tore out the old interior staircase from the 1st to 2nd floor in my house. The old staircase had 2 stringers.
I cut 3 stringers and when I put the middle stringer in it severly limits the head clearance when I go down the basement. Because of this, I would like to omit the middle stringer.
I'm about to screw and glue and I've asked everyone I know what to do and I get conflicting opinions. If some of my advisors wouldn't throw in comments about the decreased weight capacity of the staircase, that 3rd stringer would already be in the coal stove.
Location: Interior 1st to 2nd floor Stringer Length: 14 feet Stringer Lumber: 2x12 pine Tread Thickness: 1 inch Tread width: 31 inch Tread Depth: 10 inch Building Inspection: No
Is this a bad idea? Is 2 stingers enough for a stairway 31 inches wide?
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Richard wrote:

Double stringer each side. Glue and nail or screw the paired stringers. Load test a tread for the 31 inch span. It should pass the test. TB
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snipped-for-privacy@bellsouth.net schrieb:

Hallo, Richard ,
Stringer Lumber: 2x12 pine The Stringer Length: 14 feet has much more influence on the necessary dimensions of the stringers than the tread with, if You only make the treads thick enough.
Tread Thickness: 1 inch by Tread Depth: 10 inch will carry most people. To my feeling, an educated guess based on a rather similar stairs in my house, the deformation of the tread could be enough to produce a noise a the joints when You use the stairs. A bit thicker, 1.5 Inches or at least 1.25 would be welcome.
With Tread Thickness 1.5 Inches I am rather inclined to take only 2 stringers, but they need to be thick enough. A cursory calculation affirmed this by far. NO GUARANTEES! I have no inclination to end in front of an American court.
There is however another problem: Beams that are much higher ( 12 '' ) than thick ( 2 '' ) want to lay on the side. You have to make sure that the stringers remain in the upright position. In several old houses I have seen the screwed to the adjacing wall. But do not inhibit the deformation due to seasonal changes in moisture. Invent a sort of clamp or drill bigger holes into the stringers than the bolts would need and use washers.
To make it real clear or just for the fun of it: mail me at snipped-for-privacy@ideenschmiede-rh.ch
Greetings and good luck rh , a long time ago engineer for mechanical resistance (stress and strain)
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"Richard" wrote

Putting in a 3rd stringer, should not have anything to do with the head clearance. Unless: The 3rd stringer doesn't match the other 2, OR, all the stringers are not layed out for head clearance.
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The bottom of the new staircase is above me when I walk down the basements steps. Two of the stingers straddle the basement opening. The third, runs right down the center and subsequently above my head when I go down cellar.
I took the first responders advice....sort of...I put the third sringer in but moved it off center..
jerome

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Richard wrote:

Are you using risers? If so, they add quite a bit of stiffness to the treads, especially if you nail or screw the riser into the tread below. Also, you could use 2x treads. Get yourself some doug fir 2x12's.

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