Calculating residential gutter capacity

[SCGeo]

Does anyone have a helpful reference for this calculation? Is it possible to use a rainfall intensity value from an IDF curve with the roof and gutter geometry? What about the rational method?


Thanks for any replies.

 

[cvg]

you could do it, remember that your time of concentration will be quite short and the C will probably equal 1.0

 

[francesca]

You also have to consider what storm you'll be designing for: how often would you be satisfied with your gutters spilling over? The highest intensities are for 5-minute storms, presumably with higher intensities for shorter downpours which, as cvg said, would be appropriate with the short time of concentration on a roof. Do IDF curves have intensities for 1-minute, 6-month recurrance storms, for instance?

Isn't this topic covered by building codes, though? And wouldn't architects be more experienced in gutter design?

It looks like eng-tips doesn't include architects, but perhaps the ANSI Code forum can help?

 

[cvg]

if you have a flat, mansard roof - you should be very conservative on your design to prevent roof collapse or leaking. For a normal sloped roof, the gutters are more for convenience. Many houses in this area have no gutters at all.

 

[SCGeo]

Thanks for the replies. I should clarify that I am not designing in this instance, only trying to evaluate the existing system to determine its adequacy.

The ANSI code was a help. I think in this case the downspouts were undersized for the gutters that were designed.

Here is an excellent site that may help others who might need it. I had no idea that this was an architectural issue or that engineers didn't design gutters as much.

http://www.copper.org/applications/architecture/arch_dhb/gutters_downspouts/gutter_calculation.html

Thanks again all.

 

[Ron]

There is a definitive manual that has been used for many years for this purpose. It is the Sheet Metal and Air Conditioning Contractors National Association (SMACNA), Architectural Sheet Metal Manual. It gives what you are looking for.