Roof Cladding Capacity
The capacity of metal cladding profiles is determined by their geometry, the roof pitch and rainfall.
The height of the lap is the determining factor for overflow and water ingress. Therefore, the lap should be sealed if it is below minimum pitch, as is required for curved roofs and bull-nosed verandahs.
All New Zealand manufactured roof cladding profiles, except corrugate, have adequate free discharge capacity for a rainfall of 100 mm/hr. Corrugate should be restricted to a maximum length of 40 m or a 30 m² catchment area for a rainfall of 100 mm/hr, or decreased or increased dependent on the rainfall.
(see section 8.2. catchment area)
Where the rainfall is greater than 100 mm/hr, sheets are longer than 40 m or multiple roofs are designed, it is recommended to increase the minimum pitch by 1° per 10 m over 40 m.
A step in the roof, or any penetration, will require an increase in the drainage capacity of the profile required.
Where multiple roofs are drained directly or indirectly onto a lower roof, the total catchment area is the sum of both roof areas.
When penetrations concentrate the run-off into one or more corrugations or pans, the capacity must be calculated as described in Discharge Capacity.
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