There is no linear foot of gutter per downspout calculation that can be made since it is the size of the area draining into that downspout that will tell you how much volume of water will typically drain through it.
Gutter length per downspout.
Offset of more than 10 ft 3 0 m can affect drainage capacity.
The standard is about inch per 10 feet.
You should have enough gutter downspouts to effectively handle the size of your entire gutter system.
Gutter downspout sizes are 3 to 6 inches.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Increasing the pitch increases a gutter s handling capacity but the gutter may look askew over a long run.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Downspouts should be constructed with conductor heads every 40 ft 12 2 m to admit air and prevent vacuum.
For example adding one 4 inch round downspout will increase the gutter capacity by 1 255 square feet and one 3 inch round downspout would increase capacity by 706 square feet.
Please lower the maximum spacing between downspouts to see this effect.
If we have to sum it up in a single rule gutters need a downspout around every 30 to 40 feet.
The gutter outlet capacity should suit the downspout capacity.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
15 m is a practical maximum gutter length to be served by a downspout.
The above recommendations assume that you have properly sized downspouts every 40 feet.
The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts.
However too large a gutter downspout can look unattractive.
Design of roof drainage systems.
The standard is about inch per 10 feet.
I m not sure what the answer is but i know you can t do it per foot of gutter.
As with gutters a downspout s capacity must match or exceed the expected runoff.
For most homes this means installing spouts at either end of a gutter section.
To limit the effects of thermal expansion in gutters 50 ft.
Doubling the number of downspouts halves the required capacity for each.
The larger a gutter downspout the more water it can drain quickly.
Increasing the pitch increases a gutter s handling capacity but the gutter may look askew over a long run.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
You can t do the math like that.
The above recommendations assume that you have properly sized downspouts every 40 feet.
The capacity of a sloped rectangular gutter may be approximated by using a gutter cross section area not less than that of a semicircular gutter and a depth to width ratio of at least 0 75.
