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  • The 4 to 1 ladder angle rule states that for every four feet of height you climb, the base of the ladder should be placed one foot away from the wall.
  • Alternatively, a person can stand against the supporting wall and try to reach the rungs of the ladder with fingers. If the distance is correct, the ladder is safe. This is called stand and reach rule.
  • Ladders should always be placed at a 75-degree angle calculated using trigonometry.
  • When using a ladder in a sloped base, always ensure to lash the ladder or add support and leveling feet to make it more secure.
  • Using a ladder on stairs requires the use of combination ladders or alternatively a makeshift scaffold ladder.
  • Safety ladder standards stipulate the correct usage of ladders.
  • The standards should adhere at all times.
  • Using ladders in complex situations requires exercising more cautionary actions.
ladder angle rule

Here’s my choice of Attic Ladders for Safe Attic Access.

Existing rules guide every correct usage of something. Many rules govern its proper use of ladders, but the most common practice is the ladder angle rule (4-to-1) rule. The rule states that “for every four feet of height you climb, the base of the ladder should be placed one foot away from the wall” in other words, the ladder should be at a 75-degree angle.

stand and reach method of ladder angle
stand and reach method of ladder angle

You could use this simple method to determine the correct angle of a ladder.

Here, you need to stand against the supporting wall and stretch out the hand at shoulder height, the fingers should touch the rungs of the ladder.

Adjustments should be made if the ladder is too far or too close.

4 to 1 rule is quit simple, this can be expressed mathematically as;

  • The height to climb = 20 feet
  • The distance to place the base of the ladder is 20* ¼ = 5 feet

Following the 4-1 rule, this means that to climb a height of 20 feet, you need to place the base of your ladder 5 feet away from the supporting wall.

The proper angle to place a ladder is 75-degree.

Remember, the main objective of having and observing the rule is to maintain the safety of the user.

When the base of an extension ladder is placed too close to the supporting wall, making an angle of probably more than the recommended 75 degrees, the ladder could easily fall back due to inadequate support.

The ladder base could be placed too far from the supporting wall making a smaller angle in other circumstances. Here, the ladder could easily slide-off and cause harm to the user.

I know I’ll lose some of you here, but walk with me.

The correct angle for using ladders is preferably 75 degrees, so now see:

ladder angle rule 4 to 1
Ladder Angle Rule 4 to 1

The side labelled (a) is the hypotenuse (b) is the base and (c) is the height.
Trigonometry states that to find the angle between the base and the hypotenuse we use the tangent rule which is;

tan = c/b = 20/4 = 5;

The tangent of 5 is about 78 degrees.

We could also use the cosine and sine rule, depending on the measurements available. When given the hypotenuse and base, use the cosine rule. That is;

Cos (x) = a/b

When given the height and the hypotenuse, use the sine rule. That is;

Sin (x)= c/a

Using a ladder is more convenient and safe when on level ground, but it is riskier when placed on the unlevel ground such as a slope. Therefore, one needs to observe more cautionary measures to ensure that he/she is safe when using the ladder.

One way to do that is by lashing the ladder to a secure place, adding cleats and ladder leveling feet at the bottom of the ladder to ensure it’s in a fixed position, or building a work platform where the ladder will stand at a level ground.

To calculate the slope of the base, use the formula;

m = (y2 – y1) / (X2 – x1)

Where m is the gradient/slope of the base.
Y2 and y1 are the values of the y coordinates.
X2 and x1 are the values of the X coordinates.

For instance, the ladder is placed on a base that slopes from a height of 5 feet to 2 feet and the base from 4 feet to 3 feet. Calculate the slope of the base.


m=(y2 – y1)/(X2 – x1) = (5-2)/(4-3) = 3/1 = 3

Thus the slope is 3.

Remember, the ladder should always be placed at an angle of 75 degrees even when on a sloped base, and follow the ladder angle rule.

It is always preferable that one uses a ladder on level ground for purposes of safety. However, at one point or another, one will need to use a ladder on an uneven staircase.

When using a ladder on uneven ground, it is preferable to use a combination ladder. The ladder has a unique feature, including a longer side and a shorter side. Place the longer side to an even surface preferably a floor and the shorter side on top of the staircase.

Alternatively, one could make a Makeshift Scaffolding where one places a step ladder on top of the stairs and then places an extension ladder against the wall. To construct a platform, screw the two ladders together to a deck to ensure that they are healthy.

To find the slope of the stair, we use the formula:

proper ladder angle on stairs
Proper Ladder Angle on Stairs Using Tangent Rule from Bottom to Top

Similar to finding the angle for the elevation of ladders, we use trigonometry to find the angle of elevation of the stairs.

Use the tangent rule;

Tan =b/a

Similarly, you could calculate the angle on the top side of the stairs. Illustrated as;

ladder angle rule on stairs
Proper Ladder Angle on Stairs Using Tangent Rule from Top to Bottom

And therefore, to find the angle of elevation of the stairs, we use the tangent rule that is;

Tan (x) = a/b

The following requirements are set for ladders safety, according to the Occupational Safety and Health Administration (OSHA) and American Ladder Institute.

  • Ladder steps and rungs should be parallel and uniformly placed at a spacing ranging from minimum 25cm and maximum 36cm.
  • The ladder rungs and steps should have a width of 29cm or 11.5 inches
  • Extension ladders should be placed such that it extends 3 feet above the supporting surface.
  • Rungs on fixed telecommunication ladders should be placed at least 46 cm apart.
  • The centerline of the steps in step stools should be placed at least 20cm apart and not exceed 30cm.
  • The minimum recommended width for step stools is 26.7 cm.
  • Rungs and steps on manhole ladders must have a width of 23cm.
  • Rungs and steps on rolling ladders must have a width of 20cm.

Often, we’ll find ourselves required to use ladders in complex situations or rather unusual conditions. Such times, it is essential to exercise caution as accidents could quickly occur. To avoid accidents from happening, one should follow some tips on safe ladder usage, which includes;

  • Always ensure to observe the ladder angle rule at all times.
  • Ensure you face the ladder when climbing up or town.
  • Always use the three-point-of-contact while climbing a ladder, which implies that both hands should be on the ladder and one leg too or two feet and one hand placed in connection with the ladder.
  • Always ensure the ladder is lashed to a secure place when working on uneven ground.
  • Do not move the ladder when someone is on top of it.
  • NEVER place a ladder on an unstable base to obtain additional support/ height.
  • Always inspect a ladder to make sure it’s in good condition before using it.
  • Always select the right ladder for the right job.
  • Only one person is allowed to go up a ladder at any particular point.
Last Words

A ladder could be a beneficial tool and a dangerous tool at the same time when not used in the right manner. We should always ensure that we are familiar with the rules and follow all the stipulated rules for correct ladder usage from the ladder angle rule to ladder usage in a sloped base, stairs, and finally, all the do’s and don’ts when using ladders.


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