Alternating tread stairs versus standard stairs

Guidelines for how to choose the best type of stair for your application.

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More space? Choose a standard stair

Choose standard stairs for applications without space restrictions. They require more space to install than alternating tread stairs but they are also the most comfortable to use.

Less space? Choose an alternating tread stair

For applications where space is limited, choose alternating tread stairs. 68° alternating tread stairs require the least amount of space but the steeper angle is less comfortable to use. The less steep angle of 56° alternating tread stairs is more comfortable to use while also requiring less space.

What does OSHA say?

OSHA classifies alternating tread stairs (alternating tread devices) as non-standard stairs and states they are acceptable to use in applications where it is not feasible to use standard stairs.

§1910.25(b)(8)

How to determine which stair is the best fit

The three factors to consider when installing a stair are the stair angle/slope, the vertical height/rise of the stair and the horizontal projection/run of the stair.

To comply with the current OSHA standards for general industry, standard stairs must be installed at an angle of 45° or less to the horizontal and alternating tread stairs must be installed at an angle between 50° and 70° to the horizontal. The stair rise is determined by your application and vertical distance between the lower surface and upper surface that the stair will connect. The horizontal projection of a stair is the amount of floor space needed to install a stair and is calculated based on the angle and rise.

Use the chart below to estimate the amount of floor space needed based on stair height. If you have enough space to accommodate a standard stair, that is your best option. If not, an alternating tread stair is an OSHA-compliant solution.

HORIZONTAL PROJECTION BY STAIR TYPE
VERTICAL
HEIGHT
68° ALTERNATING
TREAD STAIR
56° ALTERNATING
TREAD STAIR
OSHA-COMPLIANT
STANDARD STAIR
4'
2'2"
3'11"
4'3"
6'
2'11"
4'5"
5'10"
8'
3'9"
5'9"
8'2"
10'
4'7"
7'1"
9'9"
12'
5'4"
8'6"
12'2"
14'
6'2"
9'10"
13'9"
16'
7'
11'2"
16'1"
18'
7'10"
12'6"
17'8"
20'
8'7"
13'10"
20'1"

NOTE: This chart is intended for illustrative purposes only; all measurements are rounded up to the nearest inch.

68 ATS vs Standard Stair

68° Alternating Tread Stair vs Standard Stair

68 ATS vs 56 ATS

68° vs 56° Alternating Tread Stairs

More space? Choose a standard stair

Choose standard stairs for applications without space restrictions. They require more space to install than alternating tread stairs but they are also the most comfortable to use.

Less space? Choose an alternating tread stair

For applications where space is limited, choose alternating tread stairs. 68° alternating tread stairs require the least amount of space but the steeper angle is less comfortable to use. The less steep angle of 56° alternating tread stairs is more comfortable to use while also requiring less space.

What does OSHA say?

OSHA classifies alternating tread stairs (alternating tread devices) as non-standard stairs and states they are acceptable to use in applications where it is not feasible to use standard stairs.

§1910.25(b)(8)

68 ATS vs Standard Stair
68° Alternating Tread Stair vs Standard Stair
68 ATS vs 56 ATS
68° vs 56° Alternating Tread Stairs

How to determine which stair is the best fit

The three factors to consider when installing a stair are the stair angle/slope, the vertical height/rise of the stair and the horizontal projection/run of the stair.

To comply with the current OSHA standards for general industry, standard stairs must be installed at an angle of 45° or less to the horizontal and alternating tread stairs must be installed at an angle between 50° and 70° to the horizontal. The stair rise is determined by your application and vertical distance between the lower surface and upper surface that the stair will connect. The horizontal projection of a stair is the amount of floor space needed to install a stair and is calculated based on the angle and rise.

Use the chart below to estimate the amount of floor space needed based on stair height. If you have enough space to accommodate a standard stair, that is your best option. If not, an alternating tread stair is an OSHA-compliant solution.

HORIZONTAL PROJECTION BY STAIR TYPE
VERTICAL
HEIGHT
68° ALTERNATING
TREAD STAIR
56° ALTERNATING
TREAD STAIR
OSHA-COMPLIANT
STANDARD STAIR
4'
2'2"
3'11"
4'3"
6'
2'11"
4'5"
5'10"
8'
3'9"
5'9"
8'2"
10'
4'7"
7'1"
9'9"
12'
5'4"
8'6"
12'2"
14'
6'2"
9'10"
13'9"
16'
7'
11'2"
16'1"
18'
7'10"
12'6"
17'8"
20'
8'7"
13'10"
20'1"
NOTE: This chart is intended for illustrative purposes only; all measurements are rounded up to the nearest inch.
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