TECHNICAL
MYTHS AND HALFTRUTHS AROUND
CONDENSATION AND MOULD Many will be familiar with the concepts of evaporation and condensation in everyday life. When applied to buildings, however, these principles need greater analysis. This article explores some common misconceptions around condensation and mould.
Myth 1 – New houses will not have condensation Some believe that condensation will not occur in new homes. Unfortunately, this is misguided. In 2014, researchers at the University of Tasmania used detailed monitoring and microbiological sampling to investigate condensation in three newly constructed homes – each of which was undergoing its first winter. In all three homes, significant condensation was discovered. In one, dripping originating from the underside of the low-pitched roof felt like a light drizzle. The study revealed a lack of guidance in the NCC (National Construction Code) around condensation management. In a further study funded by the Australian Building Codes Board (ABCB) in 2016, a survey was sent to building practitioners and received more than 2,000 respondents. This found that condensation was widespread across Australia and that in this aspect our code was decades behind international best practice. Whilst some recommendations from that report were incorporated into NCC 2019, these were initial steps only, which are part of an ongoing work program, they do not, in themselves, prevent condensation and mould entirely.
Myth 2 – A home that is energy-efficient will not be mouldy In 2010, the airtightness of buildings was upgraded amid changes to the NCC, which both increased the stringency of energy efficiency provisions and introduced a new standard for construction in bushfire-prone areas. This was considered beneficial as greater airtightness not only reduced heat loss
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| MASTER PLUMBER MAGAZINE Autumn 2022
and delivered better thermal comfort but also helped to prevent cinders from blowing into the building. As this happened, however, copious amounts of condensation emerged in a growing number of homes. The persistent damp, which resulted has led to other problems with mould and its deleterious effects on human health. Largely speaking, this happened because the move toward greater airtightness was not accompanied by an adequate understanding of vapour management. Indeed, the ABCB-funded condensation scoping study found that design decisions around energy efficiency were the primary factors that affected most aspects of new home design. This included risks associated with vapour management, condensation, moisture and mould. That study concluded that there was a need for an integrated approach whereby each step of improvement in energy efficiency was accompanied by suitable measures surrounding vapour control and moisture management.
Myth 3 – There is no harmful mould if you cannot see it In cool climates, condensation is most significant where surfaces are coldest. Often occupants associate condensation with single-glazed windows or thermally unbroken aluminum window frames. However, water vapour is insidious: it can move with air, it can diffuse through air, and it can permeate through porous material. Given that most buildings have materials that contain high-carbon cellulose-based mould food, the addition of water pretty much guarantees mould growth. We often don’t see it only because the action is happening in the interstitial spaces between internal finishes and external cladding. If you do see mould on the walls or ceiling, that’s likely to be the tip of the iceberg. The site of colonisation is in the dark damp interstitial spaces on the reverse side. Many of these spaces are either difficult or unpleasant to access. You are more likely to smell mould before you see it.
