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Stairway construction and geometry with open back stairs

rocket190 | Posted in Building Code Questions on

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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  1. GBA Editor
    Martin Holladay | | #1

    Studies have determined that the safest stairs are so-called "7-11" stairs -- 7 inch rise, 11 inch tread -- so you are good.

    Overhanging the tread below sounds easier than ripping your 11.25 inch treads down to 11 inches.

    The biggest problem with "open back" stairs -- stairs without risers -- is that all the dust from people's shoes ends up on the floor below. When you sweep the stairs, the dust goes everywhere.

  2. wjrobinson | | #2

    Wacko... pledge is for furniture. Never ever on floors, stairs. If stairs are a problem for you then you should have stairs with runner carpet at the least. No Pledge. No no absolutely no.

  3. Expert Member

    Rick, there is a definite advantage to overhanging the treads. That's why nosing are usually included. With open risers the mechanics of climbing a stair are made easier if your toe can extend beyond the tread above without the possibility of overhanging the back.

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