SR313 Weathertightness of flashings and the importance of upstand heights (2015)

This paper examines the weathertight performance of three common junctions in wall claddings and the approach taken to flashing these joints in New Zealand residential buildings. It makes a start towards understanding the leakage performance of joints and how they might be modified to extend their range of application to taller buildings. The joints investigated are:

• horizontal H and Z jointers between direct-fixed sheet claddings
• the window head flashing in a cavity wall
• a horizontal apron flashing at the junction between a roof and wall.

A general trend was observed for joints to resist water leakage to pressures equivalent to the upstand height head of water as long as there were no air leakage paths through the joint. Adding vents for cavity walls or gaps due to construction tolerances allowed air-carried water past the upstand at lower pressures.