How Many Downspouts For Roof

Size downspouts to fit the gutter.

How many downspouts for roof.

How many downspout installations should your gutters have. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. First you must consider how many downspouts you will need. Doubling the number of downspouts halves the required capacity for each.

Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200 square feet. The above recommendations assume that you have properly sized downspouts every 40 feet. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Determine leader or pipe size.

Calculate total roof area. If we have to sum it up in a single rule gutters need a downspout around every 30 to 40 feet. Use the chart below to figure out how many extra downspouts you need. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

Gutters and downspouts are vulnerable for obstructions caused branches and leafs from surrounding trees and similar. For most homes this means installing spouts at either end of a gutter section. 3200 square feet of roof is calculated as 3200 600 5 33 rounding up you would need 6 2x3 downspouts or 3200 square feet of roof is calculated as 3200 1200 2 67 rounding up you would need 3 3x4 downspouts one 2x3 downspout will drain 600 sq. The next factor to take into account is the pitch of your roof because the pitch will cause water to flow in a certain direction.

Rainfall intensity should always be checked with the local authorities. There are many more important factors that can change this broad rule. As with gutters a downspout s capacity must match or exceed the expected runoff. There are 5 easy steps to figure out how many drains your commercial roofing project will need.

The table is based on rainfall intensity 100 mm per hour 4 inches per hour. Calculate the total roof area by multiplying its length by width. 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. As with gutters a downspout s capacity must match or exceed the expected runoff.

One 3x4 downspout will drain 1200 sq.