Matthew: [00:00:00] Hello, everyone. Welcome to another episode of the Mindful Builder Podcast. And like always, I am joined by my co host, Hamish. How are

Hamish: I'm very well. Thanks, mate. How are you?

Matthew: I am doing pretty well today. It's, uh A nice sunny day outside and we're stuck inside.

So today we have a pretty cool guest. someone who has definitely been quite influential on my Passive House career. And I probably speak on behalf of yourself as well, Hamish. We have Dr. Cameron Munro. So how are you going, Cameron?

Cameron: Very well, thanks Matt. G'day

Hamish.

Hamish: Hello. How are you, mate?

Cameron: Good, good.

Matthew: Cameron, are you a rocket scientist?

Cameron: No, I'm an aerospace engineer by training. I can't remember ever studying any rocket science, and indeed my PhD is actually in aircraft aerodynamics. Aerodynamics is about the motion of fluid over, over aircraft, and in space

there's no, no

air,

Matthew: rocket

science.

Cameron: there's no air,

in space. So,

no, I know nothing about rocket science, but I do have some friends that are from aerospace [00:02:00] engineering that did indeed go into the spacecraft

industry.

Hamish: You know what? I actually, I, I

think Matthew, Matt, I reckon you and I created that narrative. I think you and I created that narrative. It was no one else but us.

Matthew: I tell all my clients I've got a rocket scientist on our team. So Cam, I want to go back to when you were 18, which is what, 30 years ago? Is that about right?

Cameron: 20. 20.

Matthew: so you decided to get a degree in engineering and aerospace engineering. you decide to go down this path?

Cameron: Yeah. So as a kid, I was obsessed with aircraft. knew everything about aircraft and I always wanted to do aerospace engineering through school.

So everything I did in school was motivated by making sure I got into, into aerospace engineering, which I was lucky enough to do. And I absolutely loved it. , the technology, if you're into engineering and how to build things and aircraft are very much at the bleeding edge, everything is. super optimized, and perhaps coming to what we might talk about later, one of the bits of that that really stuck in my mind was the idea that an aircraft is a system.

And you can't consider one discipline in isolation. So while aerodynamics was my specialization, you had to be thinking about structures, about controls, about their elasticity, about all sorts of other functions as well to make sure that plane was going to do what It was supposed to do.

Matthew: And then you decided to do a PhD in this, is that correct?

Cameron: Yeah, that's right. So in third year uni as an undergrad, I was here at RMIT in Melbourne. Um, there was a sticker or a poster up on the wall said, get 2, 000 to travel to Scandinavia to study for a year. I didn't really know where Scandinavia was in third year, but I thought 2000 bucks sounded pretty good.

So I ended up in Sweden as an exchange student for a year. Came back to Australia, finished up, and then went back to Sweden [00:04:00] to, to the same university where I went on exchange to, to do my PhD.

Hamish: Scott from Lab Design is also a, , aeronautic engineer, is he not?

Matthew: scientist.

Hamish: He's a fellow rocket scientist.

Is there like some kind of natural progression from being a rocket scientist and then becoming a passive house expert?

Cameron: still don't think it's rocket science. But what it is, I think, is a combination of that, systems thinking. of thinking about the different disciplines. So a building is, you've got to think about all of the different disciplines that are involved, and if you change one thing, then that's going to have implications somewhere else.

And so if you don't think about the system, Then things start falling apart and going wrong. And the other part of it, to my mind, I think, is about the idea of modelling. The idea that when you're designing a plane, you can't just whack some wings onto a fuselage and put an engine on it and take off and see what happens.

There are years and years worth of calculations of modelling that goes into that before that plane first takes to the air. to both optimize it, to ensure that it does the task for which it was designed, and then more importantly, of course, to make sure it doesn't fall out of the air. And so what brought me to, to Passive House or building, building sites was really that idea that a lot of these things can be modeled, that we know physics, we know the behavior of heat and moisture, but And we can model it, and we can predict, and we can calculate what the impact of things are going to be, so we don't need to just speculate.

Matthew: we talk about, I want to go back to where you talk about things falling apart. And we know that wetting followed by drying is amazing. That's the whole idea of what we want to do. Is that not right?

Cameron: Well, ideally, the thing doesn't get wet in the first place, but yes, we need, we need to ensure that drying exceeds

wetting potential.

Matthew: Yeah, well the house is going to get wet, is it not? Like, just due to the rain.

Cameron: Under [00:06:00] construction, in standard Australian building practice, that's true that our framing, of course, is outside for a prolonged period

of time.

Matthew: So, so, so we went to obviously adding in, and I'm going back to some basic building science here, and trying to get to the point of like where we started and why we ended up. So introducing energy efficiency into building created a problem.

Cameron: Yeah, well, or just think of it another way. Before we invented or thought of this thing called insulation, whenever we heated our buildings, we put on that fire inside to heat up the building, then that heat could travel through the walls, out through the roof, unimpeded. There was nothing to slow down the movement of heat.

And as that heat moves through the wall, it dries. It dries whatever moisture is in the wall and drives it out. as soon as we introduced insulation, which is obviously a very good and sensible thing to reduce our energy use, we're reducing that rate of drying, we're reducing the rate at which heat moves across our walls,, and therefore we risk getting condensation and moisture building up in our wall systems.

Hamish: So, I mean, what we're talking about now is physics, correct me if I'm wrong, and I guess it sort of sits under this banner now of what we call building science. What is your definition of building science?

Cameron: My definition of building science is probably to start with the human physiology. What is it that we as humans require? And fundamentally, it's about thermal comfort. So temperature. It's about air quality. We need fresh air to breathe. It's about things like acoustics and it's things like light.

And how do we provide an enclosure, a building that meets those fundamental human needs? Thanks.

Matthew: there's been many mistakes made overseas that have now sort of been made sort of aware. Do you want to talk through these and sort of how we've got to this position of where we are, where your job is now very important on all projects?

Cameron: I think it's fair to say that we're, decades behind [00:08:00] some other countries, Europe and North America being the usual countries to which we compare ourselves.

There are lots of lessons from those countries, particularly after the oil crisis and the energy crisis in the mid seventies where they went and insulated buildings and they didn't worry about air tightness. They didn't worry about moisture management and then they introduced all of these sorts of problems where the buildings just weren't going to dry at a rate that exceeded the rate of waiting and so they've made these areas and we can take those in on board in Australian practice.

What really. Gets the bean my bonnet going is when we talk about somehow Australia being unique, that we have some unique climatic conditions which make us vastly different to Scandinavia or Bavaria or wherever in the world you're thinking about. And while we're certainly not Scandinavia in terms of our temperatures, we're not that different to parts of Spain, we're not that different to many parts of Italy and certainly many parts of the U.

S. The physics is universal. there's no geographic difference in physics. You know, if you drop a ball in, in Spain, it drops at exactly the same rate that it drops in Australia or anywhere else in the world. And so building physics, the understanding of how heat and moisture moves through buildings is completely identical, irrespective of what part of the world you're in or changes of the boundary condition, that exterior climate.

of how hot or cold it is and how moist it is.

Matthew: everyone's using building physics on their building sites right now, even the old school builder who might say that all this stuff that's coming in is a load of shit. The moment you get, say, two 90 45 timbers, laminate them together to then create a structural post. That is building physics. That's changing the structure of those two timbers together.

So, we're using it. This is just a more updated approach to building science, I would say. So, do you consider the most important parts? of building physics that we need to understand?

Hamish: And why should should we care about moisture moving through walls? Like, who cares?

Cameron: the easy one to answer, I suppose, isn't it? [00:10:00] So moisture is everywhere, water vapour is everywhere in our world, but probably rule number one in buildings is water kills buildings. And the first way in which water kills buildings is the bulk water, that rain from the exterior getting into our buildings.

And what does the rain or that bulk water do? It rots any moisture sensitive material like our timbers. So we have a structural problem. But probably before the building rots and falls over. We get, , mold forming on any material like timber and paper, like facings of gypsum and so on.

And of course, mold has all sorts of implications for our health. And so we come back to what's the fundamental role of building science. It's human physiology. It's maintaining a healthy indoor environment for human occupants. So we've got to stop that mold growing. And that fundamentally comes back to managing the moisture.

Hamish: so where does building physics and I guess the modeling that you do come into

Cameron: got to deal with the ways in which water gets into our assemblies. And so rule number one is to stop that bulk water getting in. We know that intuitively. If our roof is leaking, we've got to deal with large roof leaks. But then you've got other far more invidious ways in water gets into, into assemblies.

And the two most critical ones that I spend most of my time trying to think about are air transport and vapor diffusion. So if we think of a colder climate like a Canberra or a Melbourne or a Hobart, for much of the year it's warmer inside than it is outside. And because the human occupants of this house are generating water vapor.

They're sweating as they walk around the house. They're breathing and when you breathe out, you're breathing out water vapor. You're cooking the spaghetti on the cooktop. You're having showers. You're generating moisture and you're keeping the building, building warm. And so the inside of the building has a higher vapor pressure.

It has a higher [00:12:00] vapor content than the exterior of the house. And so the water vapor wants to try and get its way outside. Now if you have a hole in your wall, perhaps around a PowerPoint or something like that, that air will move into through that hole, out through the wall. And as it moves out, it's cooling because outside might be five degrees, something like that in the middle of winter.

And as it cools, it gets towards the dew point. The dew point is the temperature beyond which that water vapor in that air starts to condense. And so you've got to stop this volume of air, this moist volume, mass of air from within your home moving out across the building. That's air transport. And that's the biggest part of this second bit of the problem beyond that bulk water, that rainwater is stopping that air movement moving out.

Matthew: And this never used to be a problem because We used to, obviously, run our fires inside, burn the gas fireplace, and it would just heat up the structure without insulation, and it would just dry everything out.

Cameron: I would dry everything up because you've got nothing in those walls. You've got no insulation there. So all the heat's just moving through and it's just drying everything out.

and so as soon as we put insulation into the walls, the exterior side of that wall assembly starts getting cold. It's, it's cold, it's temperature much closer to the exterior temperature. And the condensation is all about water vapor touching cold surfaces.

And

Matthew: Is that like your Coke can? Like, or your beer can, you

Cameron: It's exactly like the beer can that you get out of the fridge and you put on the counter.

You get those little beads of water on it that start to cause condensation. And so this water vapor is around us all the time. And it causes us, it really messes with our minds. Because if we think of a, a warm sort of typical sort of spring, summer day, 25 degrees, maybe it's 50 percent relative humidity.

You think it's pretty alright, and then if you think [00:14:00] about your winter day, when it's five degrees and it's foggy or really misty outside, you would think it's really wet out there. It's a very, that must be very humid, but the absolute humidity in that air outside is actually very, very low. It's actually dry air, even though you can see all that water vapour in it.

And this is where we get so confused about between these notions of absolute and relative humidity. So while in that, on that cold day, it's a very high relative humidity outside, the absolute humidity is actually very low. Whereas inside, you may have a more moderate relative humidity, 50 percent say, which is a healthy sort of relative humidity, But the absolute moisture content, the absolute amount of water vapor in that air is actually quite high.

So hot air can carry within it a lot more water vapor than cold air. And so one of the tricks that they often talk about in North America is if you, if you have a water leak in your home in the middle of winter and you're in say, New York or Canada somewhere where it's super cold, maybe minus 20 degrees, What you should do is open all the doors and windows and let that cold air get in, because that cold air is really dry.

And as it comes through the building, it warms up, it picks up all that water that's leaked in your house, and it carries it away. none of that feels intuitive. You know, when you first look outside on that cold winter's day, it feels like you have, very high humidity.

Matthew: So, I think everyone can probably get a pretty good idea why Cam is always the smartest person on our projects.

Hamish: And probably, One of your best allies in pre construction. So, I mean, Cam, this is all great talking about this stuff and, you know, it's like it's a nice hypothesis saying that this is what's going to happen, but how do you actually know this is going to happen? Like, what can we do in pre construction to tell us [00:16:00] where we're going to have issues in our wall assemblies?

Cameron: I think firstly you've got to understand the physics and once you do that then you can work off the principles. So a lot of good building assemblies designed for the right climate, you don't need to do anything more. You know, you don't need to model everything and if we're trying to get this at scale, we've got to bring down the cost of everything we do in high performance building.

And so if we've got for a particular climate, so where I am in Melbourne, if I've got a wall system that we've tested, that we know, works by first principles works. So in a heating dominated climate like this, we talk about that you, each layer as you move out should have increasing vapor openness.

So you're allowing that outward drying of the wall system. And as long as you've got that, then you're probably okay. Where often we come into problems is where a client might want to use some quite exotic materials. or in a retrofit where we're so constrained because we're trying to work within the confines of what we've already got.

And that's where you can really get yourself into knots and it's really, it can be quite difficult to have confidence about what the solution is going to be because there's just so many factors at play. And that's where we can use modeling. And so that's what we have hygrothermal modeling for. So hygrothermal is the interaction between heat and moisture.

And with hygrothermal modelling, so the most popular software that many use, this is, uh, software from Germany called WUFI. A WUFI is a one dimensional model. So you're taking a section through a, a wall or a roof or a floor, and you're looking at the different, layers within that building looking at the characteristics, the way in which moisture moves across those different layers and you're simulating by hour across multiple years for your particular climate to work out what the risks of moisture buildup in that assembly are, and then you can [00:18:00] try and design mitigations to deal with that.

Matthew: So, for you, simple shit works. Like, we know there's systems like a timber frame with an internal wrap, external wrap. That should just be the go to on every build? Or do you prefer to be challenged by The architect that wants to do something that hasn't been done before.

Cameron: But when we say the wraps on the inside and outside, they've got to be very special wraps.

very different to what we traditionally did back in our silver sarking days, you know, luckily we've moved beyond that now. Uh, but, but I do like a simple construction, you know, something that we know works that we have, have confidence in, let's just roll that out.

, it's really those complicated ones, which, which really do introduce challenges and we have to be cognizant also, I think that the models are always a simulation of reality and reality here is exceptionally complicated and it requires a set of input assumptions. And this is perhaps the other point to try and get through is that with something like Wolfie, you have to make an awful lot of input assumptions.

And a lot of those assumptions are heavily reliant on what the builder does on site in terms of the construction detailing and the attention to detail. And this comes back to what I was saying before about air transport, and I didn't mention it, vapour diffusion, which is the other part of this problem.

Vapour diffusion is the movement of water molecules without the movement of a mass of air. So remember before we were talking about a volume of air that moves through your power points and out through your wall and condenses? Vapor diffusion is the movement of those water molecules but the air doesn't move. and so getting that balance right and understanding how I ensure that I'm not going to get a buildup of moisture in my assembly through vapor diffusion is primarily what Wolfie is about. But more fundamentally is that air transport problem because will lead to your building fail much, much more quickly than vapour diffusion will.

And so then you [00:20:00] come back to getting the air tightness right, which is so fundamentally led by what the builders do in terms of that attention to detailing to make sure that this building is nice and airtight.

Matthew: You just said building failure. What is building failure, sorry?

Cameron: So probably wetting exceeding the rate of dry is probably the easiest way I'd prefer to that. Um, so not a building falling down in a structural sense, but rather that the, yeah, I think think of it like a bucket. You got a bucket with a hole in it and you've got a a tap coming in the top or a hose coming in the top.

You've gotta make sure that the hole at the bottom is bigger than the tap coming in the top so that the building leak, it can dry more quickly than it can, can wet. Because if you get an accumulation, if that hole down the bottom of the bucket is small, then obviously you'll accumulate water very rapidly within the bucket.

The building's very much the same. We've got to get it to dry and we've got to get it to dry quick in order to minimize the of mold and obviously rot as well.

Hamish: I'm hearing loud and clear here, Cameron, that, um, these crazy messages that you might get from some builders on a Sunday morning about different wall assembly buildups, that maybe you're outside the box a little bit, AKA me sending you messages on a Sunday morning. , I'm reading that let's just stick with what we know to help protect their buildings.

I will challenge you one day though Cam, I promise you that. I will challenge you one day. So you're not only just doing this as day job, , and modeling everyone else's homes. You've actually gone through a build journey of your own. do you want to tell us a little bit about, your own project?,

Cameron: yeah, so I've been through a couple of homes, This one that I'm in nowadays, we started around 2014 and it needed a deep renovation anyway and so I thought at that time this is an opportunity to do it right. You know, if you're gonna rip the guts out of a home, that's your best opportunity and at that time, I started doing some Googling like everybody does [00:22:00] and came across this thing called Passive House and that really appealed to my engineering sort of brain.

Because here was a set of numbers, a set of metrics, and a process by which you had to demonstrate achievement of these metrics through a modeling package. And I thought, yeah, this is just like aerospace engineering. Because if you want to fly an aircraft, you've got to demonstrate to the regulatory authority that you've hit a certain set of criteria before you can even take that plane off.

It's exactly the same thought process. And so it became, it's a very tangible sort of a thing. And it's not a subjective thing where you go, Oh yeah, you don't need that in a Melbourne climate or that's not worth the money. Do this instead. And so suddenly for me as a client, I could do, or as a homeowner, I could do the modeling and I could do the trade offs and like everybody else, I was budget constrained.

So it's like, well, Do I add more insulation to my ceiling? Or do I spend that money on triple glazing instead of double glazing the windows or doing something with the floor or whatever it may be? You're trying to find the most cost effective way of achieving an outcome. And the modeling was allowing me to do that.

So my particular project was a sort of a 1910 weather board in Melbourne. Obviously leaky sieve, absolutely freezing cold in the winter and boiling hot in the summer. It had a heritage overlay on it as well. So we had some additional constraints there. We punched out all the windows, ripped the guts out of inside.

And we were trying to get to Passive House. So I was trying to get it to Enerphit, which is the Passive House retrofit standard. At that time, I was trying to be the second Enerphit in the country and we didn't get there. So just to be clear, I do not live in a Passive House because it is not certified as such.

And this is one of the really difficult things about, about Passive Houses. These criteria are absolute. You either hit the numbers [00:24:00] or you do not. no silver medal here, there's no second prize. And in our case, our challenge was air tightness as it so often is in retrofit projects or indeed passive house generally.

We finally got to 1. 2 ACH or air change rate per hour on ours. And to hit NFE you need to hit this number of one. Now a conventional new build in Australia is anything from maybe 10 to 15 air changes. Our building before we started being an old weatherboard was probably 30 plus, even if you could.

measure

which you probably couldn't done.

Matthew: you just explain air changes, what they are for everyone?

Cameron: Yeah, so you take the volume, the air volume within a building. So how many cubic meters of air are there, conditioned air within that house are there? So in a typical house, it might be 500 to 800 cubic meters of air within that home. And then if you pressurize it at 50 pascals of pressure difference inside to outside, now 50 pascals is roughly equivalent to like a 32 kilometer an hour wind.

blowing around all sides of your building. So 50 pascals is by no means an extreme pressure difference, you know, in the real world. So it's how many volumes of that air within the home are exfiltrated or extracted out or move in or move across the building per hour at a pressure difference of 50 pascals.

So if you have 15 ACH, that means at 32 kilometres an hour wind outside, constantly, you will lose 15 volumes of air within your home

per hour.

Hamish: congratulations on 1. 2. That is actually pretty fucking incredible as someone who does this for a job. I know how air tightness can be very tricky. So I think, it would have been nice to get that one air change, right?

but 1. 2 is incredible, but I am curious to know what difference does that make? If you had have got one air change or sitting at 1. 2 air change, what [00:26:00] differences actually make to that home that you live in now? this,

Cameron: So firstly I define in terms of energy, how much extra heating energy do I have to throw into this building at 1. 2 versus say 1? And the answer is diddly squat. You know, there's, there's really no measurable, difference there at that sort of level.

So in terms of my lived experience, 1. 2 is fine. Do I want my plaque on my front door to say this was an NFID passive house? You bet your bottom dollar I

do.

I

Matthew: much does it keep you up at night?

Cameron: it after the first two or three years after we moved in, it kept me up every night and I was kept saying it was going to be engraved on my, uh, gravestone.

This guy got 1. 2 ACH. I've moved on a bit now, unfortunately, but other way to think about this, though, than just looking at your energy use is, is the building durability. So what, why do we want to achieve an airtight building assembly or partly clearly it's to reduce our energy use because there's no point chucking heat into that air if it's just going to escape through our windows and walls.

in, you know, 10 minutes, but it's also comes back to that moisture thing. So I've got to stop that moisture laden air getting into my wall and condensing. And so if I can be really tight, then I reduce that risk very substantially. And so at 1. 2 ACH versus one, again, I don't think that's a meaningful impact on durability, but if my 1.

2 ACH, if the hole in my building is concentrated at one spot, And one spot only, then there's still a risk that I'm getting all of this moisture and air getting into the building envelope at that point. Now, because we've went through, in my case, one of four rounds of lower door testing to try and get that magic one, I'm pretty confident there's not one hole, that there's in fact many hundreds of tiny little holes and cracks through our building envelope [00:28:00] that are accumulating to make that.

But that's why we've got to get airtight buildings. It's both energy and also building durability.

Matthew: And you've obviously done a lot of testing to try and find out where these holes are.

Cameron: Heaps. I think the last blow at all, there were about five or six of us there for a whole day going around trying to find the, the leaks. And it just becomes, for anyone who's ever done this, will I'm sure attest that the first few big holes are nice and easy to find. But gee, when you get down to those last sort of last little bits, it becomes a right nightmare to find

where those holes are.

Matthew: Were you originally under one, like during construction?

Cameron: No, we were, 1. 2 was the best we ever got. And that was at a post plastering stage. , know, we all learn, right? Every time we do something, we learn something new. Otherwise we wouldn't bother being here. , if I had another crack, I'm pretty sure I'd, I'd get there.

Um, but it's all, it came down to sequencing and

detailing.

Matthew: What did you do wrong? I shouldn't say wrong, but what would you, what would you go and change?

Cameron: so there were a couple of, um starter strips in the membrane that we didn't put in when we should have done. So that's just for those that might not know, you cut yourself off a little bit of your, your air tightness membrane and you put it in on say wall end plates before you. put those internal walls up, things like that, to give you something to attach to.

And so we made life hard for ourselves, but we also had some pre existing internal walls, like running down the hallway, we had our two side walls and we left those there, and so you're trying to tape along your ceiling to this gnarly 110 year old bit of hardwood, top plate, and then you're starting again on the other side, it's death by a thousand cuts.

Every time you're having to stop that membrane and restart, you're just never quite getting it 100%, no matter how

diligent you are.

Hamish: try to build a passive house when it wasn't cool. It's cool now, which [00:30:00] is great, right? And you didn't have what we have. And that is dozens of builders sharing details and, , failures and lessons and all that kind of stuff.

And I know this probably doesn't,, scratch that itch of that point too, but I think that your, and I'm going to use inverted commas here, failure has probably led to. Many, many, many successful passive house projects, certified projects.

Cameron: Yeah, oh, absolutely. One would hope so. I mean, in the last decade since I started on this, everything's changed for us, certainly for those of us that are in Victoria, but also increasingly in other states and territories too. We've got far more suppliers willing, able to provide us with materials.

We've got heaps more builders with experience doing this, or at the very least an eagerness to give this a crack. And we've got all of this, this wealth of knowledge with using Australian building techniques, Australian materials. how we do stick frame construction air tightness rather than having to google and find something in Germany that's this heavy masonry construction detail using some exotic Austrian thermal bridge detail something or other that you know we struggle to get our heads around here we've got out we're starting to develop our own ecosystem now of local solutions and local experience and it's fantastic

Matthew: And, I'm assuming you've seen huge change over the last, what, 12 years that you've been in the passive house industry.

Cameron: Yeah, absolutely. But also, also in consumer awareness, like Passive House is actually a thing. Like this is, if I'm not feeling great today, I just walk around the house and tell myself Passive House is actually a thing now. People, you know, people actually know what it is. People are asking for it. Builders want to do it.

I mean, how good's

that? Because a

decade

Matthew: open your windows and doors?

Cameron: Ha ha ha ha ha. Absolutely [00:32:00] you can. Do you want to open, do I want to open my window when I'm in Melbourne when it's 5 degrees outside? No. Do I want to open my window when it's 40 degrees, 40 degrees in summer? No. But I can. And so for the three days a year when the weather's good in Melbourne, I'll open the window.

But I only open it to hear the birds tweeting, to get that connectivity with outside. I don't need to open the window for fresh air.

Hamish: every time I get on the phone with you, I, hang up and I've just got this massive smile on my face. You're like a kid in a candy shop when we started talking about building science and I'm, I've certainly have learned. So much from talking to you. I mean, I'm so interested in passive house and it's definitely why I think we should do it at homes, but my brain doesn't quite understand the physics and it's really great to have someone like you who can explain it to, I'm going to call us a layman Ryan or a lay person in a way that we understand it.

one thing I did want to ask you is you, you don't have a fireplace in your house. Do you? But you may, may be putting a fireplace in another project. Is that

Cameron: of Hamish, not over my dead body. So my original architectures here actually had a fireplace. It was a matter of some marital dispute. there's no fireplace and I won that one. don't win all our arguments, but we win some. Uh, So, so fireplaces in any home, let alone a passive house.

So, so why don't we take the passive house side of it first, a high performance built. So let's say you build a really airtight building and you want a fireplace in that. Okay. So, The fireplace clearly needs oxygen. Oxygen is part of the combustion process. So where does that come from? In a conventional fireplace, it's coming from within the home.

And then everything has to pressure equalize. So if you're sucking air into the firebox, it's got to come in from outside somewhere. And in a conventional Aussie home, that's not a problem in the slightest because our homes leak like a sieve. So you get [00:34:00] these cold drafts coming through all the leaks that then feed the fire.

As soon as you go for a high performance home, you build an airtight home, then you don't have that make up air. You don't have a building envelope that is open enough to allow that air in. So you need a dedicated make up air supply. Is that a problem? No, not particularly. There's plenty of fireplaces on the market now that have got their, a second make up air supply.

So that's okay. But there's a much more fundamental problem with wood fires, and this applies to any type of building, and this comes back to the human physiology and human health, and whenever you burn something, you get a whole lot of combustion byproducts, things that are potentially extremely hazardous, even in small doses, like carbon monoxide, which you can't see or smell, but far more critically for wood fires is the particulate matter.

You know, we can think of it as smoke, or little bits of stuff that comes off, little carbon based, um, molecules that, that come off the fire. So that's, that's the smoke that you see, but it's also a whole lot that you don't see. You know, you might smell, oh, I smell a wood fire, well part of what you're smelling there is the particulate matter.

that comes in. And particulate matter is graded by its size. So the diameter of these little balls, of material. And so you have things from PM10 all the way down to PM1. And the number is the diameter of those, those particles. in micrometers. So these are tiny little things that you can't see.

And so the ones we're most worried about are the ultrafine particles under one micrometer and up to maybe two and a half is often where we use the fine particulate matter, PM 2. 5 you'll often see mentioned around. And when you burn stuff in a wood fire, you are generating vast quantities of PM 2. 5 and lower.

So these really fine particles. And those particles get [00:36:00] breathed in, they get through our lungs because they're so fine, they're not getting filtered by the little hairs throat. And they get into our lungs and they get absorbed into the bloodstream. So they're so fine, they just get absorbed.

And there's lots of evidence now about the health implications, both on our respiratory system, even all the way through to like causing cancers and stuff. And so we know intuitively, you know, if you spend a few years living in New Delhi or Beijing or some really polluted city, that can't be good for us.

And a large part of that is this particulate matter. But this particulate matter is also generated by wood fires. And so If you go outside in somewhere when there's, you know, in a country town where there's lots of wood fires going in the winter, you'll smell all that smoke and it's pretty horrible.

Inside a house, you'll get the same. You've got an open fire, obviously that's super hazardous because there's nothing stopping that particulate matter building up your building, but even if you've got a closed firebox, so a door on your, on your fireplace, You might say, well, how can I possibly be getting this particulate matter into my room?

Well, guess what? You're feeding that fire. And how do you feed that fire? You open the door. And when every time you open the door to chuck that wood in there, this particulate matter is literally flooding into that room. And it's going to take hours after that's flooded into the room for it to dissipate out.

Irrespective of whether you've got an airtight home or not, this is going to take donks. And in the meantime, while that floats around in your room, you can, you won't see it. It's not like it's really a lot of smoke everywhere. You're breathing it into your lungs and into your body. And so it's deeply hazardous.

So if you come back to what do we build buildings for, it's got to be about healthy buildings. Why would we go and stick something in our buildings that then just gives us this enormous amount of particulate

matter?

Matthew: So, should we ban fireplaces then?

Cameron: Can we? Is that a [00:38:00] possibility?

Matthew: Would you want to ban fireplaces?

Cameron: Can we do it tomorrow? Can we, is government still open? Can we legislate today? Yeah, absolutely. when I say that, there'll be people out there that are going, oh, but these are lovely and cozy and we love the, you know, all this other stuff. And yeah, I get that.

But you know what? Going back a hundred years ago, people thought smoking was a pretty trendy thing to do too. our expectations, our understanding of what is healthy and what is not changes over time. And the evidence on the impact of particulate matter on our health is rapidly evolving.

And it's always revolving in the direction of saying it's more hazardous than we thought it was.

Matthew: What about if you put it outside, like if people have their fire pit away from the house?

Cameron: So that's a much harder one, isn't it? So, have a couple of thoughts on this. So firstly, you can get what are marketed as smokeless fire pits. So they've got a sort of a, they encourage a secondary combustion and they reduce smoke. so someone who's really keen on a fire pit could look at those as an option.

but they're not truly smokeless by any means because any form of combustion cannot be complete. In a rural setting, I'm somewhat more comfortable with that, particularly if it's windy, because of course the smoke will dissipate far more readily than it would in an indoor environment.

In an urban setting or a regional town, I find that very problematic. because we've got to consider the ethical implications of this. This is not something that just affects us individually. It's a bit like the smoking versus passive smoking debate. You know, if I choose to smoke, well that's on my head, but if I choose to smoke in an environment with lots of other people and therefore exposing them, is that ethical?

And so if I live in, say, Melbourne, and I have a wood fire either inside my house or a fire pit outside in the back, then I am clearly contributing to the local air quality that my neighbors have no choice but to absorb. I [00:40:00] just find that ethically very problematic.

Hamish: chatting with you cam and also chatting or listening to, uh, the guests that we actually recorded previous to this one, absolutely swayed me from, putting a wood fire in my current home. So we have recently moved into a house that is incredibly terrible from a performance point of view.

And it's a far cry from what we used to live in. And I thought, you know what, I'll just whack in a 500 secondhand wood fire because, you know, I'm a builder. I come across all the time, but I've also got two young children and I've got two young children who have had asthma and one does have asthma. And I thought to myself, I can't do it.

I can't put a wood fire combustion heater inside. morally, ethically, whatever you want to, however you want to look at it, I just can't do it. Sitting outside

around a campfire

a fire pit, you know, that's something I really enjoy doing. And challenged again, right? Like, because I'm, I'm hearing all of this evidence and I'm, I'm thinking about it.

I'm thinking about my health and my kid's health and, Is that now going to be like a sometimes food for me rather than every Saturday night? I don't know, but it's certainly got me thinking.

Cameron: and I would submit to that, you know, there's no way we'd expose our kids to passive smoking. Now, even if We would have smoked. We certainly wouldn't do it front of our children.

so why should we treat wood fires any differently? Now, I think the only reason why we treat them differently is awareness or lack thereof.

the evidence is now increasingly clear on this. So we, we, we, we ought to re respond. But, but we come back to this, there's, this seems to be this innate human thing isn't there of that coziness of the wood fire and the, when the flames are lapping around, I get that subjectively, it's a great thing, but we can't move away from the objective reality.

That being exposed to that is a very bad thing for our health.

Matthew: I'm being the devil's advocate here. Why don't I just go get a gas [00:42:00] fireplace?

Cameron: Ha ha Well, if it's externally flued, I mean, to be fair, gas does burn cleaner. And it's a more controlled thing too. This is the other thing that I just, I'm going to bring it back to wood fires without going off too far on a tangent on gas. But, yeah. You know, you've got to test wood fires, there's a test standard before you can sell them and you've got to demonstrate a certain emission rate, like grams per, I can't remember what the units are now, per kilogram of wood or whatever, and it's tested in a standard, to a standard test condition.

It's a bit like the same way you test a car on a cycle for its fuel economy, but in the real world, our fuel economy of our cars bears no semblance to that in the test standard. And in the same way, we just chuck any old crap wood we can find in our fireplace. And we're all probably really bad at knowing how to regulate the airflow in that wood fire and let it burn down before we put more wood on or whatever, you know, however you optimize it.

But of course, the test standard assumes really dry wood, a whole bunch of ideal parameters, which are not happening in reality. And so the difference between the What the test standard says in terms of your emissions and your real world observed emissions for when Hamish whacks on the fireplace and Chuck's on the wood, is not just a 20 percent difference.

It's an order of magnitude. You might get 10 times more emissions. It's really large. And so, so much of this comes down to the human operation. But even if you operate as per the test standard, you're still going to flood your room with these, these particular matter every time you open that. Fireplay, firebox spill.

Hamish: I So hopefully you win that, win that,

Matthew: argument.

Hamish: I don't want us to, I guess, leave on a, downer, like poo pooing fireplaces. And I, genuinely hope that our listeners can see that Cam is incredibly intelligent when it comes to building physics and the health and comfort of our buildings.

Fireplace has been one thing that he's very knowledgeable [00:44:00] about, but obviously very knowledgeable about the performance of our buildings and, Why we see cams valuable in optimizing our projects in pre construction and then the benefits of doing all of that. We're actually hoping to get, cam on as a regular guest and, unpacking some specific, things within a building that people might want to know about.

So, if you do have something you want to talk about, uh, or, or a question that that you want, , answered from Cam, you obviously, he's a very knowledgeable person and, you know, Matt and I can put in our two bulbs work as well because we are in the space of building.

Healthy, high performing, uh, energy efficient homes. , so yeah, Cam, thank you so much for coming on

Matthew: I

look forward to having more of these chats. Cam. We, uh, we look forward to having you on again.

Cameron: Thank you very much.