NZBC Clause B2, Durability, requires fifteen years to perforation for claddings easily accessed for replacement. Fifteen years is also required for internal gutters and downpipes, and five years for external gutters.

NZBC B2 requires 50 years’ durability for flashings that require the removal of cladding above to be replaced, while table 20 of NZBC E2/AS1 only requires 15 years’ durability for such flashings. The COP recommends the higher figure as good trade practice and in many cases, lower life-cycle costing.

Generally, higher durability than the minimum requirements can be achieved by using materials and methods outlined in this COP, with no maintenance of coatings other than washing areas which are not naturally washed by rain. Elements more difficult to replace, or to access for maintenance, should be constructed of more durable material.

Normal Maintenance means work recognised as being necessary to achieve the expected durability of a given building element.

According to B2/AS1, normal maintenance may include:

  • Washing down surfaces subject to wind-driven salt spray and contaminants.
  • Re-coating protective surfaces.
  • Replacing sealant seals and gaskets in joints.

Although roof or wall cladding can be easily accessed and therefore easily replaced, the same cannot be assumed for flashings. Flashings might be embedded in plaster or behind other building elements, making them hard to replace without removing cladding or other building features such as windows.

Cladding material may be described as hidden, sheltered or exposed. Some flashings may have sections falling into all these categories, in which case the worst case (sheltered) should prevail in material selection.

All metal roof and wall cladding and accessories must be designed and installed to comply with the durability requirements of the NZBC. NZBC requirements relate to performance, however, and do not necessarily relate to aesthetics or cost of replacement. Any pre-painted cladding will change colour over time, and partial replacement would be visible. The roof cladding could have deteriorated, although not perforated, within 15 years and still comply with the NZBC, but customer expectations may not be met.

Good design, correct selection of materials, and good installation and maintenance practices are required to achieve optimum product lifespan. 

Clause Number:
Draft Clause: