Part three - Managing moisture - gaps in the NZ building code

The New Zealand building code includes a section (E) dedicated to moisture. In theory, the “provisions ensure conditions for healthy, safe and durable buildings.”

Unfortunately, in reality, the oversimplification of thermodynamics/building physics within the code means many buildings that are deemed to ‘meet code’ are not necessarily “healthy, safe and durable”.

For example, the code is almost entirely silent on thermal bridging, a known driver of moisture development within building structures (not to mention energy loss and reduced occupancy comfort). While E 3.1 and 3.2 do include general statements about avoiding the likelihood of moisture and fungal growth, there are a lack of specific requirements in the acceptable standards or verification methods on how to demonstrate this to be the case.

E3/AS1 includes a very basic equation requiring a thermal break of minimum R 0.25m²°C/W for a very specific scenario where steel framing is used with thermal break strips, and other than that, nada.

The presence of this one requirement has two key issues:

First, it oversimplifies the mechanics of heat transfer at a thermal bridge and secondly, in the absence of any other guidance in the code, it gets applied to scenarios where it just doesn’t make sense.

As the building code is improved to (hopefully) start to support our move towards net-zero emissions by 2050 we will hopefully see improvements that will also address the gaps that currently mean ‘code compliant’ buildings are not necessarily moisture-free buildings.