Stairway construction and geometry with open back stairs
I’m proposing a 6′ wide L shaped open stairs. The treads will be 3.5″ thick doug fir glulams. The stringers will also be glulams. I was planning on attaching the treads with angle iron brackets. The treads will be approx 68″ wide and will be self supporting from the outside stringers.
My proposed stair geometry is an 7-1/8″ rise, 11″ run. I’m manufacturing the glulams, so I can make the depth of the treads to what I need, but without further machining, the treads are currently 11.25″ deep. I chose these dimensions to have a comfortable rise, and so that the maximum space between the bottom of the treads is (7.125″ – 3.5″ = 3.625″). (Less than the 4″ sphere test mandated by code)
I presume there is no advantage to have the treads overhang the tread below since the back is open?
Also, please comment on my stairs geometry? Does this seem like a comfortable compromise?
The stairs in my house are currently a 7-5/8″ rise with a 10″ tread + a 1″ nosing. They meet code and the so called principles of good stair design, but personally I think they are too steep, especially when coming down the stairs. Freshly Pledged and wearing socks, they are borderline dangerous. I can’t imagine how an 8″ rise and 9″ run is code legal in some places.
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