Sizing downpipes downpipes are sized for the areas that discharge into them.
How many downpipes for roof area uk.
The building regulation s part h drainage and water disposal requires that adequate provision is made for rainwater to be carried from the roof of buildings.
Using clause e1 table 5 see figure 2 at a roof pitch of 45 for this example.
Design area effective area 5 x 10 x 1 29 64 5m run off 64 5m x 0 022 l s per m 1 42 l s from chart 125 x 100 gutter with 76 ø downpipe appears suitable but check.
Figure 1 an example of a roof with a total plan area of 98 m.
Determine minimum number of downpipes.
The length of the roof is 8 7m for this square house as 8 7m x 8 7m is 76m total floor space.
The program will calculate the most suitable circular and rectangular downpipe sizes.
So for our example the half roof area is as follows.
As you can see with an effective area of 40m 2 there will be no issue using any of these systems and configurations.
This is because larger roofs require bigger volumes of water to be diverted away from them during periods of rainfall.
The roof slope height is 6 98m.
Usually the size for the largest collection area on the roof is used to size downpipes throughout.
Floplast guide to guttering and roof area.
From figure 3 5 a in as nzs 3500 3 the maximum catchment per downpipe is 47m 2.
Frequency and positioning of outlets downpipes calculate the number of outlets per run.
A rainwater downpipe is a pipe that is used to direct rainwater away from a building typically from roof guttering to a drainage system it is sometimes also referred to as a downspout drain spout roof drain pipe or leader.
Divide the main roof into catchments of this size and any left over area can be entered again to find a down pipe size for this smaller area.
Because this is only one half of the roof we will need to double this number to find the entire roof area 121 45m.
To calculate the minimum number of downpipes divide the roof catchment area by the allowable maximum catchment per downpipe.
Select 100 x 50 rectangular downpipe.
63 mm diameter downpipes.
However if our effective roof area were 50 m 2 then we would not be able to use a level half round gutter with a stop end outlet ie the downpipe at one end of the gutter rather than in the middle.
8 7m x 6 98m 60 73m.
Min number of downpipes roof catchment area.
The answers for downpipe size are in mm.
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.
The number of downpipes you need will depend on the size of your roof and your chosen style of guttering.
