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.
Most people do maintenance retro-actively, they mow lawns, wash the car or remove debris from gutters when they see it needs to be done. While rain washed metal roof surfaces do not generally require maintenance to comply with warranty conditions, it is always good practice to conduct regular inspections for dirt build up or deteriorating components, which can be removed or replaced respectively before they contaminate the body of the roof. Unwashed areas of roofing and wall cladding do require regular maintenance to comply with warranty conditions.
Section B2 – Durability of the NZBC gives live cycle requirements for materials of 5, 15 or 50 years “subject to normal maintenance”.
In most applications profiled metal cladding and associated materials have a 15 year requirement to comply this clause. Cladding used as structural bracing, and hidden elements, may require 50 year durability, and exposed spouting and downpipes, 5 years.
The use of pre-coated or pre-finished roof and wall cladding with a minimum 15-year warranty, has led to the belief that no maintenance is required for that period. That is incorrect. The terms of the warranty state that maintenance is required, and the performance of metal claddings is entirely dependent on the environment. See 4.3 Metal Performance.
Continued maintenance and over-painting will enhance the decorative appearance and extend the lifespan of all roof and wall cladding, and rainwater products.