The stair plan below shows the normal stair stringer locations and size as C12x20.7, which is a C channel that is 12 inches deep that weighs 20.7 pounds per foot.
Other structural steel channel sizes used are C10x20 and MC12x31 but there is no limit as to what type of steel sections to be used, even wide flange beam commonly known as I beam can be used as stair stringer.
Even though different steel sections are used as building stair stringers, one thing that is very common among all these steel sections is the depth – it is very rare to see stair stringer different from 12 inch deep.
For structural steel tubes commonly used are HSS12x4x1/4 or HSS12x2x1/4 – these sections are 12 inches deep x 4 inches wide x ¼ inch wall thickness.
There are two types of stair construction presented in there stair section shown here. The stair shown on stair 2 is formed to the side of the stringers i.e. the stair treads and risers are welded to the sides of the stair stringers.
The other method shows the stair treads and risers are formed and welded to the top of the stringers. With this method the stair stringer can be anything because the stringers are hidden below while on the other design half of the stringer is exposed.
Steel Plates are also used as stair stringer, typically half inch thick by 12 inches wide. It is being used the exact same way as steel channels particularly welding the treads and risers to the sides.
Like steel framed stairs, wood framed stair stringers also use 12 inches deep members typically 2x12 sawn lumber, vast majority of homes use 2x12 sawn lumber for stairs.
For longer span stairs microllam LVL or parallel lam is used, glulam members sometimes are used on stair stringer.
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