Topic Title

Does anyone know of a simple way to calculate and locate downspouts?

What I am looking for is a way I can determine the quantity and locations of downspouts for small residential construction. Previously we have been determining this in the field with the trades but now since we are growing and increasing the number of homes under construction and the number of trades we are using it will be more efficient to put this on our prints.

Any tips or tricks??

I use Architectural Graphic Standards. There's a step-by-step there that will teach you how.

Hello Tony,

Since you are in Ohio and many communities use the Ohio Plumbing Code (International Plumbing Code, modified).

Go to Chapter 11. Table 1106.2 will give you the horizontal area per diameter of downspout and Table 1106.8 will give you the horizontal area per diameter of semi-circular gutters.

The problem with these tables is that they use diameters, and, of course, most downspouts are rectangular and gutters are ogee or box. Just inscribe the diameter into the shape of downspout or gutter you are going to use.

In previous codes, the rainfall for sizing was 4 inches per hour, now you can use the map included in the code.

Any questions, send me a note offline.

Thanks Daniel.

I will have to look this up. I am sure we have a copy of the plumbing code around here somewhere.

Try the Architectural Sheet Metal Manual by SMACNA, Inc.


Sheet Metal and Air Conditioning Contractors National Association
Tyson's Corner, Virginia