I have a 21" plumb from my backyard wood deck to the concrete below. My problem is that the concrete is not even, it slopes away from the house. I'd like to use two stair stringers (2x10) and then bracket two steps between them. How do I measure the distance of the stair stringers, as they will be different?
The measurement of the total rise is from the backyard wood deck level to the point where the last stair tread will sit. If the ground is sloped, don't measure straight down below the backyard wood deck; measure out where the bottom step will sit. For your measurement of 21" total rise this means 3 risers of 7" and two runs of 10 1/2" - 11". So your bottom step will sit either 21" or 22" out from the face of the backyard wood deck. Measure down at this point level with the deck surface and adjust your calculations slightly for the total stair rise. Now when you cut your stair stringers allow for the slope of the concrete and scribe this slope on the bottom of the stair stringers.
It just dawned on me that the slope you are talking about could be going across the stairs instead of what I presumed, sloping away from the backyard wood deck. If you are talking about the slope going across the stairs, ie. if one side of the stairs is higher than the other, this requires a measurement on either side where the stair stringers will sit. Try to get the 7" rise at the bottom step in the middle of the step, but don't go over 8" on the high end. (See also Backyard Wood Deck Stairs on Uneven Ground.)
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