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Alternating Tread Stair Measurements, Dimensions

Technical Resources

Alternating Tread Stair 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.

Alternating Tread Stair 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

Alternating Tread Stair Horizontal Projections

VERTICAL HEIGHT/RISEHORIZONTAL RUN
STEEL, 56°STEEL, 68° ALUMINUM, 68°
24"N/AN/A15.96”
30"N/AN/A18.59”
36"28.93”N/A20.41”
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

Alternating Tread Stair Standard Dimensions

56° STEEL68° STEEL68° ALUMINUM
Minimum floor-to-floor height36"42"24"
Maximum floor-to-floor height240"240"216"
Overall height, standard handrailsHeight + 42"Height + 42"Height + 42"
Overall height, optional handrailsHeight + 5¾"Height + 5¾"Height + 3¾"
Overall width23"23"23"
Recommended minimum floor opening, width35"35"35"
Recommended maximum floor opening, length70" + ⅔ floor thickness62" + ⅖ floor thickness62" + ⅖ floor thickness
Minimum riser height6.417"7.517"7.175"
Maximum riser height7.7"9.02"9.566"

Additional Dimensions and Pricing

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

Alternating Tread Stair Head clearance

PDF Downloads

Alternating Tread Stair 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
BOTTOM FOOTING BOLT PATTERN, STEEL ALTERNATING TREAD STAIRS
TOP TREAD/LANDING BOLT PATTERN, STEEL ALTERNATING TREAD STAIRS
BOTTOM FOOTING BOLT PATTERN, STEEL ALTERNATING TREAD STAIRS

Options For Alternating Tread Stair Installations That Requires 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.

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 or Reduced Footing

The footing at the bottom of an alternating tread stair can be extended or reduced to accommodate certain installation requirements.

Handrail Extension

Extended safety for roof hatch alternating tread stair applications.

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