There is no limit to downpipe size or eaves gutter size.
Roof area per downpipe.
Average catchment per downpipe roof catchment area.
Dividing the total flow from the roof by the number of downpipes will give the flow per downpipe.
Roof area m gutter flow litres sec roof area m downpipe at centre half round 76mm 0 7 34 0 8 38 112mm 1 8 86 2 6 125 squareflo 3 2 154 3 8 182 125 68mm downpipe 3 8 182 4 6 221 82mm downpipe 4 0 191 4 9 235 regency 4 2 202 4 7 226 highflo 5 4 258 6 0 289 stormflo 110mm 11 1 534 12 4 598 160mm 12 5 601 14 0 673 downpipe at end half round 76mm 0 5 24 0 6 29.
This can be calculated using the following formula.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Average catchment per downpipe roof catchment area no.
The first thing you need to work out is the area of the roof that will collect rainfall which is known as the effective roof area.
Roof catchment area allowable maximum catchment per downpipe 223 8 47 4 76m five downpipes are required round up to the next whole number step 6.
It is the roof area the pitch of the roof and the number of drops downpipes coming down from outlets in the guttering around the building determine the flow we will need to know these to calculate the flow capacity for you.
Determine the average catchment area per downpipe.
Working out the size of your roof.
Of downpipes 223 8 5 44 76m.
Multiplying that number by the local maximum rainfall intensity 6 8 inches per hour yields an adjusted square footage of 7 480 square feet.
The code limit is 150mm for dp s and 26 800 sq mm for flat eaves gutters.
The 6 in 12 pitch factor 1 1 multiplied by 1 000 yields an effective area of 1 100 square feet.
In some cases roof area m gutter flow litres sec roof area m downpipe at centre half round 76mm 0 7 34 0 8 38 112mm 1 8 86 2 6 125 squareflo 3 2 154 3 8 182 125 68mm.
Choosing the right style of guttering downpipes.
Calculate the number of outlets per run.
Doubling the number of downspouts halves the required capacity for each.
To calculate the average catchment per downpipe divide the roof catchment area by the number of downpipes.
Dividing the total effective roof catchment area by the catchment area for the gutter selected will give the number of downpipes required.
This is not normally a whole number so it is rounded up to the nearest whole number.
Therefore this roof should be equipped with 6 inch k style gutters.
Per downpipe 223 8 47 4 76m 2 five downpipes are required round up to the next whole number step 6.
You can choose a downpipe size and calculate the number required and the corresponding eaves gutter size.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Average catchment per downpipe roof catchment area there are many possibilities for downpipe positions.
Frequency and positioning of outlets downpipes.
