Dimensions and measurements for alternating tread stairs
Measuring guidelines
Alternating tread stairs are built to exact, vertical height measured from (A) where the top landing of the stair attaches to the upper, finished floor to (B) the lower, finished floor where the foot of the stair will be secured.
Sloped floors
If the finished floor is not level, the slope will impact the vertical height of the stair. One way to accurately measure vertical height on sloped floors is by using a string/line level.
Use the horizontal projections chart on the right to determine the approximate location of the foot of the stair based on the stair angle and estimated height.
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Alternating tread stairs used for roof hatch accessSpecial guidelines apply when measuring for alternating tread stairs that will be used to access a roof hatch. |
Head clearance OSHA §1910.25(b)(2); IBC §1011.3
OSHA and IBC require stairs to have minimum head/vertical clearance of 80 inches. These requirements are based on the slope of standard stairs. Due to the steeper angle of alternating tread stairs, we recommend a minimum head clearance of 88.2 inches for 56° alternating tread stairs and 108.7 inches for 68° alternating tread stairs.
Horizontal Projections
| VERTICAL HEIGHT/RISE | HORIZONTAL RUN | ||
| STEEL, 56° | STEEL, 68° | ALUMINUM, 68° | |
| 24" | N/A | N/A | 15.96” |
| 30" | N/A | N/A | 18.59” |
| 36" | 28.93” | N/A | 20.41” |
| 42" | 33.11” | 23.08” | 23.08” |
| 48" | 37.25” | 25.66” | 25.66” |
| 54" | 41.37” | 28.2” | 28.2” |
| 60" | 44.91” | 30.28” | 30.71” |
| 66" | 49.07” | 32.83” | 33.2” |
| 72" | 53.21” | 35.36” | 35.36” |
| 78" | 57.33” | 37.86” | 37.86” |
| 84" | 61.44” | 40.04” | 40.35” |
| 90" | 65.15” | 42.56” | 42.56” |
| 96" | 69.27” | 45.05” | 45.05” |
| 102" | 73.39” | 47.28” | 47.54” |
| 108" | 77.49” | 49.78” | 50.02” |
| 114" | 81.59” | 52.27” | 52.27” |
| 120" | 85.38” | 54.75” | 54.75” |
| 126" | 89.49” | 57.01” | 57.23” |
| 132" | 93.59” | 59.5” | 59.69” |
| 138" | 97.68” | 61.98” | 61.98” |
| 144" | 101.77” | 64.45” | 64.45” |
| 150" | 105.62” | 66.74” | 66.91” |
| 156" | 109.71” | 69.21” | 69.38” |
| 162" | 113.8” | 71.68” | 71.68” |
| 168" | 117.89” | 73.98” | 74.14” |
| 174" | 121.97” | 76.45” | 76.61” |
| 180" | 125.85” | 78.92” | 78.92” |
| 186" | 129.94” | 81.38” | 81.38” |
| 192" | 134.02” | 83.7” | 83.3” |
| 198" | 138.11” | 86.16” | 86.3” |
| 204" | 142.19” | 88.62” | 88.62” |
| 210" | 146.09” | 91.08” | 91.08” |
| 216" | 150.17” | 93.41” | 93.54” |
| 222" | 154.25” | 95.87” | N/A |
| 228" | 158.33” | 98.33” | N/A |
| 234" | 162.4” | 100.78” | N/A |
| 240" | 166.32” | 103.12” | N/A |
Standard dimensions
| 56° STEEL | 68° STEEL | 68° ALUMINUM | |
| Minimum floor-to-floor height | 36" | 42" | 24" |
| Maximum floor-to-floor height | 240" | 240" | 216" |
| Overall height, standard handrails | Height + 42" | Height + 42" | Height + 42" |
| Overall height, optional handrails | Height + 5¾" | Height + 5¾" | Height + 3¾" |
| Overall width | 23" | 23" | 23" |
| Recommended minimum floor opening, width | 35" | 35" | 35" |
| Recommended maximum floor opening, length | 70" + ⅔ floor thickness | 62" + ⅖ floor thickness | 62" + ⅖ floor thickness |
| Minimum riser height | 6.417" | 7.517" | 7.175" |
| Maximum riser height | 7.7" | 9.02" | 9.566" |
View overall height, horizontal run, weight, and pricing by type of alternating tread stair:
Carbon steel, powder coat finish
Standard connection details
The top tread/landing and the bottom footing of an alternating tread stair bolt into place using customer-supplied bolts or studs with a minimum 1/2" diameter. The drawings below illustrate the standard bolt patterns for steel and aluminum alternating tread stairs.
DOWNLOAD PDF DRAWING
DOWNLOAD PDF DRAWING
DOWNLOAD PDF DRAWING
DOWNLOAD PDF DRAWING
Micro platform
Bolts to the top landing/platform of the stair to add an additional 10" to the length. Customer-supplied struts are required when using a micro platform.
DOWNLOAD PDF DRAWING
Extended mounting plate
Welded to the existing mounting plate on the top landing/platform of the stair to provide a custom bolt pattern for attaching the stair.
DOWNLOAD PDF DRAWING
Extended or reduced footing
The footing at the bottom of an alternating tread stair can be extended or reduced to accommodate certain installation requirements.
DOWNLOAD PDF DRAWING