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.
All downpipes that discharge onto a lower roof must have a spreader to dissipate energy and ensure wide distribution of the water. A spreader should be used over multiple troughs.
For corrugate, a spreader should not discharge into a lapped trough. When using the COP calculator, discharge may be into a lapped trough of a trapezoidal or a trough profile.
The area of discharge holes from a spreader should equal the cross-sectional area of the downpipe.
The 5.8.1 Maximum Area Above Spreader Calculator enables users to determine the maximum upper roof area that a lower roof can discharge for a given combination of rainfall intensity, roofing profile, and lower roof pitch.
Before using this calculator, please read 5.3 Roof Drainage Design.
Calculate the maximum area above a spreader by entering 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.