Roof Area Per Downspout

Rainfall intensity should always be checked with the local authorities.

Roof area per downspout.

The table is based on rainfall intensity 100 mm per hour 4 inches per hour. Gutters and downspouts are vulnerable for obstructions caused branches and leafs from surrounding trees and similar. Large gutters can hold more water. A high slope moves water more quickly and if gutters have trouble dealing with a lot of water in a short period of time an extra downspout can alleviate that issue.

Up to 6 12 7 12 8 12. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. The roof plan area that is drained by each downspout is plan area 40 x 40 1600 sf given the area factor b in table 10c the design area is design area plan area x b 1600 x 1 05 1680 sf from table 10a column b2 the area drained per square inch of downspout is 130 sf. Max area of roof draining to one down.

This wizard makes it easy to calculate the roof design area by providing various shape calculations and the calculation for vertical walls area per international plumbing code ipc. The more roof surface above the gutters the more rainwater will be caught and funneled down into those gutters. Gutters come in many sizes. Secondary cause of gutters not working properly is improperly maintained or failing.

Smacna s new downspout and gutter sizing calculator enables the user to manually enter the design area of the roof or use the design area wizard for the calculation. Doubling the number of downspouts halves the required capacity for each.