Downspout sizes must not exceed the bottom width of the gutter.
Gutters and downspouts gutter sizing table.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
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.
Capacity from using table 1 1 and 1 2 should be com pared with local code requirements.
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.
To limit the effects of thermal expansion in gutters 50 ft.
Table 1 2 rainfall data and drainage.
Table 1106 6 size of semicircular roof gutters for si.
3 by 4 inches 1 200 square feet.
The gutter outlet capacity should suit the downspout capacity.
Use the chart below to figure out how many extra downspouts you need.
The saf perimeter systems gutter downspout capacity table click to enlarge relates downspout size to gutter sizes.
2 by 3 inches 600 square feet.
The downspout size must suit the bottom width of the gutter.
The resultant calculation q cia will be the flow rate for the roof design.
Downspouts should be constructed with conductor heads every 40 ft 12 2 m to admit air and prevent vacuum.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Offset of more than 10 ft 3 0 m can affect drainage capacity.
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.
1 inch 25 4 mm 1 square foot 0 0929 m 2.
Doubling the number of downspouts halves the required capacity for each.
Size downspouts to fit the gutter.
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.
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.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
15 m is a practical maximum gutter length to be served by a downspout.
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.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Use the chart below to figure out how many extra downspouts you need.
The size of the downspout should be constant through.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
In response smacna s technical resources department has created a free downspout and gutter sizing calculator.
