Code of Practice v3.0 Online
The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
A gutter’s discharge capacity increases with the depth of water over the outlet. The best way to increase the head is to discharge the open end of the gutter into a rainwater head or sump. Swirl at the outlet reduces its performance, so positioning of the outlet is important.
To avoid any water back-up if the drain capacity is overloaded or obstructed, an air-break should be provided for all downpipes to ensure that water does not back up the downpipe.
Discharging water off an inert surface onto unpainted galvanised rainwater goods can cause corrosion. See 4.11B Normal Catchment.
Horizontally run PVC downpipes and gutters require a greater provision for expansion than metal, particularly if they are painted a dark colour. Horizontally run PVC downpipes and gutters should have a maximum length of 9 m.
Placement of downpipes significantly affects gutter and downpipe calculations.
Use this table to select the correct internal dimensions of common downpipe sizes for use in the online calculator at 5.4.7 Gutter Capacity Calculator.
Material | Size | Nominal Diameter (mm) | Internal Dimension (mm) | x-Section Area (mm²) |
---|---|---|---|---|
PVC | 65 x 50 | 65 x 52 | 3380 | |
100 x 50 | 102 x 51 | 5171 | ||
65 | 63 | 3138 | ||
80 | 76 | 4537 | ||
110 | 98 | 7626 | ||
160 | 143 | 16157 | ||
200 | 178 | 25157 | ||
250 | 224 | 39840 | ||
280 | 253 | 50823 | ||
315 | 274 | 59610 | ||
Steel | 75 | 75 | 4466 | |
100 | 100 | 7940 | ||
90x50 | 90 x 50 | 4400 |
Before using this calculator, please read 5.3 Roof Drainage Design.
To calculate downpipe capacity, select the type of building, type of gutter and overflow (yes or no). Complete the rest of the data by changing the values in the designated fields.
For an explanation of each element, please click on the corresponding question mark.For rainfall intensities, refer to NIWA’s HIRDS tool or the 5.3.2 Rainfall Intensity.