Gutters And Downspouts Gutter Sizing Table

Table 1106 6 size of semicircular roof gutters for si.

Gutters and downspouts gutter sizing table. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. As with gutters a downspout s capacity must match or exceed the expected runoff. Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200 square feet. 2 by 3 inches 600 square feet.

15 m is a practical maximum gutter length to be served by a downspout. The downspout size must suit the bottom width of the gutter. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. Size downspouts to fit the gutter.

Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. Offset of more than 10 ft 3 0 m can affect drainage capacity. The size of the downspout should be constant through. Downspout sizes must not exceed the bottom width of the gutter.

Gutter dimensions are selected from the horizontal gutter sizing table based on the slope of the gutter to the downspout s and the gutter capacity based upon the roof flow rate in gallons per minute. 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. Table 1 2 rainfall data and drainage. 1 inch 25 4 mm 1 square foot 0 0929 m 2.

Use the chart below to figure out how many extra downspouts you need. Doubling the number of downspouts halves the required capacity for each. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. 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.

Capacity from using table 1 1 and 1 2 should be com pared with local code requirements. To limit the effects of thermal expansion in gutters 50 ft. 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. The size of semicircular gutters shall be based on the maximum projected roof area in accordance with table 1106 6.

As with gutters a downspout s capacity must match or exceed the expected runoff. Downspout sizing in sizing downspouts the following considerations apply. 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.

3 by 4 inches 1 200 square feet. The gutter outlet capacity should suit the downspout capacity. 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. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.

The resultant calculation q cia will be the flow rate for the roof design.