Technical resources 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.

Alternating tread stairs used for roof hatch access

Special guidelines apply when measuring for alternating tread stairs that will be used to access a roof hatch.

How to measure for a roof hatch installation

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.

HEAD CLEARANCE FOR 56° ALTERNATING TREAD STAIRS
HEAD CLEARANCE 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"
ADDITIONAL DIMENSIONS AND PRICING

View overall height, horizontal run, weight, and pricing by type of alternating tread stair:

Carbon steel, powder coat finish

Carbon steel, galvanized finish

Stainless steel

Aluminum




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.

TOP TREAD/LANDING BOLT PATTERN, STEEL ALTERNATING TREAD STAIRS
DOWNLOAD PDF DRAWING
BOTTOM FOOTING BOLT PATTERN, STEEL ALTERNATING TREAD STAIRS
DOWNLOAD PDF DRAWING
TOP TREAD/LANDING BOLT PATTERN, ALUMINUM ALTERNATING TREAD STAIRS
DOWNLOAD PDF DRAWING
BOTTOM FOOTING PATTERN, ALUMINUM ALTERNATING TREAD STAIRS
DOWNLOAD PDF DRAWING



Options for installations that require special connections

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.

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.

EXTENDED MOUNTING PLATE
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.

EXTENDED FOOTING
DOWNLOAD PDF DRAWING
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