For many building facility managers and homeowners across Australia’s East Coast, soaring summer humidity has left a dangerous legacy — mould. Respiratory infections and irritation to the eyes and skin are just some of a long list of potentially serious side effects from exposure to mould.

According to Ashburner Francis mechanical engineer and environmentally sustainable design (ESD) expert, Lara Bailey, last summer’s conditions created a perfect storm. “For a prolonged period, we experienced 24/7 humidity,” she explains. Back in January, Sydney endured record-breaking humidity and other states too rang in the new year with sweltering conditions.

Image: Ashburner Francis mechanical engineer and environmentally sustainable design (ESD) expert, Lara Bailey. / Supplied.

A high percentage of moisture in the air at a specific temperature is known as ‘relative’ humidity. During Australia’s summer, relative humidity did not dip sufficiently to inhibit mould growth.

Mould loves moisture. When air conditioners are in operation, inside temperatures are cool.

What’s problematic is the infiltration of warmer, moist outdoor air (especially during storm seasons). When this air lands indoors, it can result in condensation on cold surfaces — creating favourable conditions for mould growth.

Bailey pinpoints “leaky” buildings and homes as part of the problem. In some cases, buildings and homes in warm climates are designed to be open to the outdoors — to make the most of cool breezes. She’s referring, of course, to large windows, louvres, and indoor/outdoor dining areas — not all of which will be 100 percent airtight when closed.

This past summer has pushed even the best insulated homes and/or ‘passive’ buildings to turn to air conditioning. Architect and Architectus Conrad Gargett Principal David Gole says, for the first time, his own South-East Queensland hinterland home (which he himself designed as ‘passive’) now requires air conditioning.

“We always wanted a really sustainable house,” Gole says. “We generate our own power, have our own waste treatment and collect our own water. Up until now, we never envisaged having to draw on energy to cool the entire house!”

David says after repeated cycles of trying to “manually” combat humidity, the time has come to install air conditioning to help remove moisture from the air. “We’re taking this step not only for our own health but the health of our visitors too.”

The goal is to remove moisture from interiors (ideally, at the point of creation). Natural ventilation and air conditioning can assist — but not simultaneously. Bailey warns “if the air conditioning is running, the place needs to be entirely sealed up.”

When designing mechanical engineering services such as air conditioning, Lara says communication and education are key. “We need to understand precisely how a building or home operates,” she says. “Don’t be aspirational about how your building or home is going to be used. Be realistic.”

If some occupants routinely open certain parts of the building whilst the air conditioning is running, Lara and her team need to know. Aged care facilities are a good case in point, where large numbers of residents may opt to have their windows and doors open — while the adjacent common areas are air conditioned.

‘Mixed-mode’ services may be a suitable solution for sites like these. Here, both natural ventilation strategies and air conditioning can co-exist. But only if they’re well designed. Lara says getting the balance right is a “very nuanced task”.

At entrances and exits, air locks (that trap air between two doors) may help maintain consistent internal air temperatures. Similarly, air curtains (where air gushes down above entranceways) can assist in countering exposure to warmer outdoor air when people enter or exit a building.

In the case of specialist commercial buildings, Bailey points out that high-tech moisture-removal systems can be very effective at prohibiting mould growth. However, the cost of these systems is, of course, prohibitive for the mass market.

“Buildings must be ‘fit-for-purpose’ well into the future,” Gole says. “We’re dealing with very different climatic conditions now, so we need agile and responsive engineers who can rise to those challenges.”

Sometimes those solutions come with higher upfront costs. “More than ever, engineers need to provide clear communication, risk profiling, and plenty of design options, so building owners and managers can make informed decisions.”

Closer to home, Bailey suggests homeowners look closely at rooms where moisture is most likely to be found, year-round. Think kitchens, bathrooms, and laundries. “Consider ways moisture can be removed from those rooms, otherwise it can be absorbed into surfaces — creating a prime breeding ground for mould.”

Exhaust systems, that extract moisture and release it outside the building, are a good place to start. Ideally, exhaust fans should be connected to light switches that trigger their operation. Bailey says the addition of in-built timers can also be beneficial to ensure exhaust systems run long enough to remove any lingering moisture.

For new homebuyers, Bailey encourages the market to look for designs that favour natural cross-ventilation (where windows and/or doors are located opposite or adjacent to one another). According to Lara, well-shaded windows (ideally with awnings) are another must-have.

“Large windows are often a big part of architecturally designed homes — they look great and help connect occupants to nature,” Bailey says. “But without adequate sun protection, these windows may add to solar heat gain inside the home, increasing the air conditioning load on your property.”

As Gole notes: “It is no longer ‘business as usual’. For the health of occupants, we really need to rethink how we manage our air quality and focus on building systems that can mobilise to accommodate different weather events.”

Main image: Shutterstock

Branko Miletic

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