Roof drainage layout and calculations.
Rainwater gutter design calculations.
On a rainfall intensity of 75mm hr roof pitch not exceeding 50ยบ gutters running full.
Divide these areas by the local rain fall rate in inches per hour to determine the actual roof area to be served by the gutter diameter.
Calculate effective maximum roof area b c 2 x length of roof area in m installation tips for gutter fixings onto wooden fascias use 25mm x no 10 round head rust proof screws.
Doubling the number of downspouts halves the required capacity for each.
Round 3 inches 706 square feet 4 inches 1 255 square feet.
For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e.
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.
Working out gutter slope as a general rule gutter slope is set at 1 4 inch per 10 feet of guttering.
For the most up to date rain intensity data visit noaa s website and use precipitation intensity as the data type.
To limit the effects of thermal expansion in gutters 50 ft.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Refer to bsen 12056 part 3.
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Resources aluminum series acm series column covers fastener series zinc series testing data aama pdf astm pdf gutter sizing sheet metal gages order literature northclad gutter size requirement calculator this calculator uses current data to calculate the required size of gutter as well as number and size of downspouts based on your input.
Size downspouts to fit the gutter.
From chart 1 2 it is determined that a 9 5 in 241 mm half round gutter should be used.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
15 m is a practical maximum gutter length to be served by a downspout.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
Area and flow in table 1 4 are based on 1 in 25 mm of rainfall per hour.
Downspout sizes must not exceed the bottom width of the gutter.
This wizard makes it easy to calculate the roof design area by providing various shape calculations and the calculation for vertical walls area per international plumbing code ipc.
Subtracting 3 4 for under the roof edge and 1 8 outside edge allowance this is the width that is available for the rainwater to enter the gutter total width of a flat piece of building material maximum total gutter drop before any downspout this assumes 4 7 per hour maximum rain intensity.
