Enter the depth of water up to the secondary inlet of drainage and the extra depth of water above the secondary inlet into the calculator to determine the rain load.

Rain Load Formula

The following equation is used to calculate the Rain Load.

RL = 5.2*(ds+dh)
  • Where RL is the rain load (psi)
  • Ds is the depth of the water up to the secondary inlet of drainage (inches)
  • Dh is the depth of the water above the secondary inlet of drainage (inches)

To calculate the rain load, add together the depth of water up to the inlet and above the inlet, then multiply by 5.2.

What is a Rain Load?

Definition:

A rain load is a measure of the pressure acting on a roof with a certain depth of water resting in the drainage system of the roof.

How to Calculate Rain Load?

Example Problem:

The following example outlines the steps and information needed to calculate rain load.

First, determine the depth of the water up to the secondary inlet. In this case, the depth of the water here is 2 inches.

Next, determine the depth of the water above the secondary inlet. In this example, this depth is 1.4 inches.

Finally, calculate the rain load using the formula above:

RL = 5.2*(ds+dh)

RL = 5.2*(2+1.4)

RL = 17.68 psi