Gutter/downspout sizing

[Markus Keller]

I know I had a PDF that had some math for sizing gutters and downspouts based on roof size, etc. Can't find it, really needed it today.
Does anyone have one, know what I'm talking about? I thought I got it off IN at some point.
Big McMansion house, 4" gutters with 3" downspouts, very steep multiple roofs; water is literally making craters at the bottom of the downspouts. No extensions of course, top gutters just drop onto the shingles.
Seems cheesy for the $1 million+ sale price. Wrote it all up. I'm guessing I'll be hearing from the developer.
Thanks, Markus

[Raymond Wand]

Sizing Gutter Systems - Fine Homebuilding Article (http://www.finehomebuilding.com/how-to/articles/sizing-gutter-systems.aspx)

Copper.org: Architectural Details: Gutters and Downspouts - Intro (http://www.copper.org/applications/architecture/arch_dhb/gutters_downspouts/intro.html)

eGutter - Architectural And Commercial Box Gutter Profiles Manufactured To Your Specification. (http://www.egutter.com/SUPPORT/Commercial-Gutter-Profiles-Color-and-Sizing)

[Philip]

Are these al or steel gutters. If so, I have only seen one 4" gutter in thirty-years, and it was a steel gutter. I can't believe they are using vinyl gutters for this house. I can not understand the thinking that puts a 5" gutter when the cost difference to go 6" is nominal. Sometimes a 3x4 drain on a 5"gutter works. There are usually other indications if the gutter is over flowing.

[Markus Keller]

Thanks for the links Raymond. Great info. Just what I will probably need in the next few days.
Phillip, you mean other indications like the algae, long divets along the walls that run parallel to the gutters.
Wanted to add a smiley face but can't figure out how under the edit function.
Markus

[Philip]

On gutters I also look to see if water is getting between the gutter and the gutter board. You will find that is the case many a time. You will see black drip marks off the gutter board, and yes, water can run uphill.:)