Gutters And Downspouts Gutter Sizing Table

15 m is a practical maximum gutter length to be served by a downspout.

Gutters and downspouts gutter sizing table.

In response smacna s technical resources department has created a free downspout and gutter sizing calculator. Use the chart below to figure out how many extra downspouts you need. Use the chart below to figure out how many extra downspouts you need. Table 1 2 rainfall data and drainage.

Downspouts should be constructed with conductor heads every 40 ft 12 2 m to admit air and prevent vacuum. 3 by 4 inches 1 200 square feet. Now architects engineers designers and contractors can easily and accurately size downspouts and gutters according to the specifications in smacna s architectural sheet metal manual 7th edition 2012. 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.

The saf perimeter systems gutter downspout capacity table click to enlarge relates downspout size to gutter sizes. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. The size of the downspout should be constant through. As with gutters a downspout s capacity must match or exceed the expected runoff.

Capacity from using table 1 1 and 1 2 should be com pared with local code requirements. Size downspouts to fit the gutter. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. The resultant calculation q cia will be the flow rate for the roof design.

To limit the effects of thermal expansion in gutters 50 ft. As with gutters a downspout s capacity must match or exceed the expected runoff. 2 by 3 inches 600 square feet. Downspout sizes must not exceed the bottom width of the gutter.

The downspout size must suit the bottom width of the gutter. Water capacity values of a gutter downspout system is calculated using the height head of water a gutter can hold the outlet orifice size of the downspout and the quantity of downspouts used. Doubling the number of downspouts halves the required capacity for each. Offset of more than 10 ft 3 0 m can affect drainage capacity.

Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. The gutter outlet capacity should suit the downspout capacity. Downspouts of less than 7 00 sq in 4515 sq mm cross section should not be used except for small areas such as porches and canopies. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200 square feet. It is possible to use a mix of gutter sizes a mix of downspout sizes and quantities to accommodate the theoretical gallons per minute draining from a roof during in climate weather. Table 1106 6 size of semicircular roof gutters for si. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.

1 inch 25 4 mm 1 square foot 0 0929 m 2.