In old homes we had (and have still in those not retrofitted) lots of energy flowing through the building elements: walls roofs and floors. This was due to lack of insulation and heaps of air infiltration. This energy flow dried out the building elements and the air infiltration managed internal moisture inside the home. On top of that we built with materials that could handle getting wet provided they dried out.
These older homes had water leaks and interstitial condensation but dried out and in general didn’t have the same moisture issues. Now New Zealand and Australia is insulating and air tightening both in new homes and in retrofits. In this short reflective article from Dr Lstubrik he points out how this is not unique; it’s been done in Canada, USA and Europe and we don’t need to do it the hard way as the knowledge is available.
Just adding insulation in both new buildings and in retrofitting old buildings is not risk free. We need to understand the physics and make the changes needed: controlled ventilation (continuous mechanical); control layers for water, air and vapour; and the education to know what to do.
Partially retrofitted leaky building Photo SELtd
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Reference Lstiburek, J.W. (2025). Insight-151: Déjà vu All Over Again… Building Science Corporation.
Abstract: This article reflects on the historical failures of insulation programs in North America and how New Zealand and Australia are currently repeating these mistakes. It explains the relationship between energy flow and drying potential, highlighting how high insulation levels reduce the “drying energy” available to building elements. It advocates for the use of robust control layers and mechanical ventilation to prevent moisture-related failures in modern builds.