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.
Good design can avoid frequent maintenance, but preventative maintenance may provide the most economical solution. This can be achieved by enhancing the product before installation, or by painting metal cladding at nominated intervals.
Where the underside of metal roof cladding is subject to contaminants such as salt at the gutter line, an over-flashing should be inserted between the roof and the gutter to prevent deposits which lead to 'inside out' corrosion. This flashing can become a sacrificial one where dissimilar metals are used for gutters or spouting, and where splashes and contaminants can corrode the roof cladding. See 8.4.4.4 Eaves Flashing.
Where the gutter line micro-environment is likely to be severe, the underside of metal cladding should be painted using a two pack epoxy primer or elastomeric polyurethane paint before installation.
Building underlay alone can provide this protection if carried down into the gutter, but does not have a 50-year durability if exposed to UV and can give rise to flutter noise if lapped too far into the gutter.
Where roof cladding is exposed to the elements from the underside, it should be included in the maintenance schedule for unwashed areas.
Seagulls perching on ridgings or parapets on buildings can cause damage from rubbish dropped onto the roof, and from their alkali droppings. Discouraging devices such as wire or spikes can be used to prevent this. Unpainted aluminium or AZ coatings are particularly prone to attack from alkali.