Roof Area Per Downspout

Doubling the number of downspouts halves the required capacity for each.

Roof area per downspout.

Up to 6 12 7 12 8 12. Rainfall intensity should always be checked with the local authorities. Large gutters can hold more water. Secondary cause of gutters not working properly is improperly maintained or failing.

The table is based on rainfall intensity 100 mm per hour 4 inches per hour. Max area of roof draining to one down. A large roof is going to move a lot of water which means the downspout locations may need to be adjust to compensate. 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.

Roof area square feet per linear ft of gutter underneath. 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. Gutters and downspouts are vulnerable for obstructions caused branches and leafs from surrounding trees and similar. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Gutters come in many sizes.