Chief troublemaker to present conference keynote

The Building Physics Forum is coming up on October 12 in Sydney and online. Organised by AIRAH, the event unites experts on ventilation, moisture and condensation management and building envelopes. It’s a highly technical community that is also renowned for its passion and energy.

This year, the keynote speaker promises to stir up even more conversation and debate. With an official job title of Chief Troublemaker at Energy Vanguard, Allison A. Bailes III has a doctorate in physics from the University of Florida and more than 20 years’ experience in the field of building science. He writes the popular Energy Vanguard Blog, and will be presenting “A house needs to breathe … Or does it?”

HVAC&R News spoke to Bailes ahead of his appearance at the Building Physics Forum.

You have a reputation for stirring up trouble. Can you share an example?

One that’s gotten the most pushback of anything I’ve written about is powered attic ventilators. My first article on the topic (way back in 2011) got 169 comments before the post was closed.

Some people really like these things, even though they can do harm by backdrafting natural draft combustion equipment or sucking in moist air and growing mould. And the truth is they don’t really help with cooling much anyway unless your attic is poorly insulated and has a lot of air leakage. It’s always better to insulate and air seal to keep the heat out of the house rather than try to vent the heat from the attic with a mechanical device.

In your experience, where do these myths come from?

They come from faulty thinking. A builder we used to work with, for example, was convinced that the wood flooring she installed in a new house cupped because the house was too airtight. In reality, the floors cupped because of moisture from the damp crawl space below.

Another way people get the wrong idea is by hearing something that sounds plausible from someone else and then not doing their homework to find out if it’s true. A lot of people call Tyvek HomeWrap a vapour barrier, even though it’s about as vapour-permeable a material as you can get. Why do they think that? Because their supervisor or workmate called it a vapour barrier.

There is an ongoing debate in Australia about raising the energy efficiency of homes by improving airtightness, and the concern that this will lead to condensation and mould problems. What is your position?

Can an airtight house have condensation and mould problems? Yes. Is it because of the airtightness? No. It’s because of a lack of understanding that a house is a system.

An airtight house with condensation and mould probably has an elevated humidity indoors. In a dry climate or in cold weather, outdoor air leaking through the building enclosure will help to dry things out and keep the indoor humidity lower. If an airtight house has elevated humidity, it needs ventilation with dry outdoor air or dehumidification.

But actually, an airtight house is less likely to have condensation and mould in cold weather/climates. When it’s cold outdoors, the indoor air is more humid than outdoors. If it leaks into a wall cavity and finds cold sheathing, it can accumulate, causing rot and mould growth. So airtightness really reduces the likelihood of moisture and mould problems.

What are you hoping people will take away from your keynote presentation at the Building Physics Forum?

Well, I hope they’ll leave with a strong design to get a copy of my book as soon as possible. Just kidding (partly). I’d like to see attendees have a better grasp of the fundamentals of building science. You know, house-as-a-system, control layers, good HVAC design, how to achieve good indoor air quality …  I’m always distilling and refining my understanding of building science, so maybe even the experts will pick up something that helps them do the same.

I’m really looking forward to presenting at the event! I’ll be staying up all night, sleeping all day, and standing on my head a lot so I can be in tune with all you Aussies on October 11!

For more information and to register for the Building Physics Forum, click here.