Determining the minimum durability requirements for roof and wall flashings can be tricky. Minimum durability requirements are placed on the flashings dependent on their location and ease of replacement by Building Code clause B2 Durability. However, flashings also need to remain serviceable for the life of the cladding.
B2/AS1 Table 1 requires that hidden flashings, such as behind brick veneer, stucco or a spandrel panel, must have a durability of not less than 50 years. Flashings that require the removal of cladding (stucco, EIFS and sheet materials) above the roof to allow flashing replacement must also have a durability of not less than 50 years.
Difficult to replace or hidden flashings must have at least the same durability as that of the element that covers them. Where flashings are behind brick veneer, the expected life of the flashing is likely to be a minimum 50 years. For flashings behind profiled metal or weatherboard wall cladding, a minimum of 15 years as is required.
Where claddings perform a structural function such as wall bracing, which has a minimum 50-year durability, the flashings are required to be just as durable.
Flashings that are exposed or partially exposed or are readily accessible are required to meet a minimum 15-year durability.
Two-part flashings as shown in E2/AS1 Figure 7 could be used to allow a lesser durability to the lower easily replaced section. The upper section would require greater durability when behind stucco and other claddings that would be damaged should the flashing need replacing.
For an E2/AS1 scope cladding that has been BRANZ Appraised, the flashing durability must equal the serviceable life of the cladding (assuming that the flashing is not easily replaced).
Reproduced from BRANZ Guideline January 2015