Downspouts

Reference data and engineering information about downspouts for miscellaneous applications.

downspouts

Overview

Engineering reference data for Downspouts in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Symbol	Description	Unit
$x$	Input value	—
$y$	Output value	—
$k$	Conversion factor	—

5 rows

Capacities of clean, vertical downspouts without obstructions for draining roof areas, based on a rainfall intensity of 100 mm/hr (4 in/hr).
Downspout Size(mm)	Downspout Size(inches)	Roof Area(m²)	Roof Area(ft²)
50	2	65	700
65	2 1/2	120	1300
80	3	205	2200
100	4	430	4600
150	6	1255	13500

Source: engineeringtoolbox.com

Practical Considerations

Design Rainfall Intensity: The capacities in the table above are based on a standard rainfall intensity of 100 mm per hour (4 inches per hour). The local design rainfall intensity must always be verified with local building codes and authorities.
Obstruction Allowance: Gutters and downspouts are vulnerable to blockages from leaves, branches, and other debris from surrounding trees. This potential for obstruction should be considered during design, potentially by increasing the specified downspout size.

Interactive Charts

Roof Framing

References

Original Source

Source: engineeringtoolbox.com