| To Convert, enter in one, answer appears in the other. (Rounded to nearest) | ||
| Instructions: Enter the horizontal roof catchment area in square metres for the section of roof you desire,(ie plan area) . Enter the roof slope in degrees. Choose a location, or alternatively enter a known intensity, but ensure the location is set to "I prefer to enter a known intensity". Click the check box if the eaves gutter slope is steeper than 1:500 (eg 1:200). Press calculate to obtain the required number of downpipes and eaves gutter cross sectional area. |
| Eaves Gutters: For sizing eaves gutters, the most efficient (and desirable) cross section, is width = twice the depth. The plumbing code assumes this in these calculaions, so don't vary too much from this criteria. The width and depth values shown above are rounded up to the nearest 5mm, and are shown only to give an idea of the size of the gutter. Pick a standard gutter that is close to these dimensions. |
| Downpipes: Check the number of DP's required, if the figure is say 0.1, then that DP is only 1/10 full. You will be guilty of gross overdesign if you use this. A smaller DP should be used. If you have the case of say, 3.25 number * 150 dia DP's required, then you may choose to split the catchments to have 3*150 & 1*100 dia DP's. However, it is normally better to keep all DP's the same size and accept 4 * 150 DP's. |
| Rectangular Downpipes:
The previous page Further instuctions gives the Code's conversion equivalent from circular to rectangular. As an explanation for the cross sectional area difference, you will note that the DP capacity is governed by the size of the entry orifice, not by any pipe flowing full formula. Therefore to compare circular to rectangular downpipes we must compare the circumference (as in the weir formula) not the cross sectional area as in the pipe flowing full formulas. So to use rectangular down pipes, find a circular DP size that fits the number of DP's you require. There is a field that allows you to use any size you like, thereby not limiting you to the standard pipe sizes. Having found this, find the circumference (2 * 3.1416 * radius), then calculate a square or rectangular pipe with this circumference. |
| Overflowing
Check out the notes on overflowing and fail safe design here, Making overflow provisions |