SR298 Rigid sheathing and pressure equalisation in New Zealand (2013)

The use of rigid sheathing is increasing in New Zealand construction. One purported benefit of rigid sheathing is that it increases the pressure equalisation performance of the wall, thereby making the wall more weathertight.

Potential urban densification in Auckland may mean typical residential details will be used in taller buildings outside of the current scope of NZS 3604 and E2/AS1. The higher wind pressures associated with taller buildings may mean pressure equalisation determines the performance limit of residential construction details.

This study reviews some of the research on pressure-equalised wall systems and concludes that, although there is theoretical support that rigid sheathing will improve pressure moderation, this improvement will only be marginal in typical New Zealand residential construction.

Since pressure differences will exist across the cladding in real situations, knowledge of joint leakage as a function of pressure and rainfall characteristics would be desirable. This could define the performance limit of residential construction details and allow decisions to be made as to whether to include rigid sheathing (from a durability perspective as opposed to a improved pressure moderation) or to change to a different style of construction, e.g. a curtain wall.