we already even talk about insulation.

So

Cam, what is insulation?

Well, I think we need to start, well, well what is insulation

is about reducing heat transfer.

Yep.

But in order to understand how insulation works, we need to

understand how heat transfer works.

So there are three ways in which heat can transfer, conduction,

convection and radiation.

So we take each of those one at a time.

Conduction is a material property.

So different materials have different rates at which heat conduct across them.

And conduction is about the, um, the atoms within a, a ma a, a

lattice of a, of a solid material like a mele or glass for example.

Or even timber And heat is, is energy.

It's the excitation of those atoms.

So they vibrate.

Yep.

And when they vibrate, they hit the atom next to 'em and they transfer

that energy and they do that across that solid material that's conduction.

So that conduction is something that happens.

Cross salt convection is the movement of air.

It's air, warm air from one space, moving to the cooler space,

carrying heat energy with it.

And that happens a lot in our buildings and is one of the reasons why air

tightness is so important to Enish.

And the third one is probably the trickiest one, conceptually to under step.

And that's radiation, that's electromagnetic, uh, energy.

So a, a material when it's heated will emit radiation in all directions.

And then that will transfer to, uh, an adjacent material that be absorbed.

So this is about the characteristic, and this is where color becomes

important because different materials have different weight rates at which

they emit electro radiation and absorb electromagnetic radiation.

So a material that's a dark color, like black, we'll have a higher absorption.

Which is a better ability to absorb radiant energy and a light color will

tend to, uh, have lower absorbed.

So you're saying that with all these cancels and local governments now

wanting to remove black roofs that could potentially be in a, in a

climate where cool climate, but we need a heat that could be a bad thing.

Well, it depends.

So, so colors like dark claddings can be beneficial too.

So, uh, in a healing dominated climate like an Melbourne or a Canberra or

somewhere, it is true that a darker colored roof sheet will obviously make

that roof space significantly warmer on a warm day than a light colored roof sheet.

Uh, but it also means that the systems is drier because you have much Grady

drier and drying potential within that roof space because of the, the

ability for that to absorb the heat.

And then allow, uh, they allow drying.

So maybe a bit off topic for a second with this.

Is it the heat urban island effect?

Are the roofs that we're designing, like should we be going more

lighter color or darkened color?

I think heat urban, um, I think that is about landscape and concrete mass.

Yeah.

Rather than, and and lack of trees.

Trees.

And this is where I'm actually, this is actually what I wanted to

get at is like, is are we blaming the wrong thing for this issue?

Well, I think it, it can contribute.

I mean, if you looked at a satellite image of a, an urban suburban area, obviously

the roof area is a significant part of the tunnel fraction of that surface area.

But the roads asphalt.

Yeah.

A dark color.

Yeah.

And is, you know, 30% of our surface area of our seas is road.

Yeah.

So that's gonna contribute disproportionately.

So, yes, to an extent, I think this is somewhat overplayed, but if we just

bring it back to buildings for a second.

If you design your building and the load well.

The color of the cladding and the roof sheet are far less material than

if you design your building poorly.

I, I actually have a note down here saying dark colors, does

it matter in passive house?

Or we could extend that to high performance homes.

And I think we've kind of touched on this before with, in other podcasts

where we start talking about, um, that ventilated and drainage cavity because

does a light or dark roof actually have that impact given its, I guess,

separation from that insulation layer?

If that cavity is really well ventilated, then clearly the cover of

the cladding is far less important.

Yep.

But they're, they're will always be some heat transfer from the roof sheet sheet

through the cladding into your insulation and then into the building itself.

Yeah.

But it, as you go up through the, from code to high performance to passive

house, the effect of the cladding color on performance of the building declines.

Yeah.

So yes, it's still important, but it's secondary or tertiary

versus to so many other things that you can do with the building.

Whereas if you have a really poor building, pre-built building,

then yes, the cladding color absolutely has an effect.

And so if you put monument on the roof, then in the summer in

Western Sydney, you are gonna bake.

So you say poor, poor performing house.

But we had a passive house in Mascot Vale where originally the

designer designed it with a darker color to get the PHBP across line.

But actually it was a white, and by the end of the project, which I had no idea

about this, and the clients had no idea.

It was actually white.

I, we lost one kilowatt hour across the whole boom, which

meant we were now failing.

And so this is where context matters, I think.

'cause one kilowatt hour per square meter for annum, which is like part

of these metrics for using passive house is really significant when

you are targeting something like 50.

Yeah.

Matches this magic number.

So one divide by 15 is obviously a large number, but we need to bear in mind your

coil homes are the north of a hundred.

Yeah, yeah, yeah.

So one unit out of a hundred is dly squat one dead of 15 is really interior.

And just to close out the whole dark color versus light color thing, that

would probably have an impact more or less of an impact if you had a

cold roof scenario and a warm roof scenario in Washington because, and

I'll probably let you expand on that a little bit because that does then feed

into insulation then where insulation sits and its impact in the building.

Yeah.

Yeah, it can, it can do.

Uh, so if it's a cold roof, again, it depends how well

isolated that roof space is.

Yep.

Um, but you've got a, a bigger,

a lot of these sort of like, well that depends because there is,

every situation is different.

And I think that's actually really important to acknowledge.

And I think this is where we come back to rules of thumb.

You know, we talk about like, uh, like the NCC talks about this, you know,

you need so many square millimeters per linear meter of opening in order

to ventilate a wall over a roof.

And that we have all these rules of thumb and they are based on one or two empirical

studies in Germany, Austria, New Zealand, wherever it may be with one context, one

wall type, maybe a few different ones.

That doesn't necessarily apply to your particular brick ER project in kind.

Or wherever it may be.

And so context matters.

Understanding the physics of what's going on matters because you can use

that rule of thumb to then say, well, that's my starting point, but my

particular project has these particular attributes, which makes it riskier.

Therefore I err towards having more ventilation.

Yeah.

But on the other hand, this project has the attributes which makes it

less risky, so I can be a bit more, uh, not, not have to require as much

in the way to as those openings.

So history of insulation, we probably think back to like the house I

live in now, something built around like the fifties, sixties, nothing.

We've gone from nothing to having something but now introduced a problem.

Yeah.

And, and so what are we doing insulation for?

We're trying to reduce the rate of heat movement and in so doing that also

reduces the ability for the system to dry.

And just to go back to those three things that you talked before,

conduction, convection, radiation.

We're talking about convection here,

so we're talking about all three.

So, okay.

Heat transfer a possibility.

Is this by all three of those.

Okay.

In different ratios depending on what element it is.

So conduction is a material property.

Yeah.

If I have a block of wood and I heat one side of that wood and I measure the

temperature at the other end of that wood.

Yeah.

Then obviously I'm expecting very little heat transfer.

Intuitively we know that to be right because wood is a, you know,

uh, has a low, so conductory.

Yep.

By comparison, if I get a bit of steel, uh, the other end will be hot to touch.

And if I get aluminum, it'll be even hotter again.

Yeah.

So it's no still houses, no aluminum windows with foil suing

all of those things.

So really, yeah.

Intuitively, Dion is the thing that we, I think we all kind of get, we know that low

thermally conducting materials are better.

Well, I get it now.

Yeah.

And, and, and, and so this comes to things like, like glass.

Yeah.

So everybody with their standard four mil glass, although my windows are

terrible, if only I had thicker glass, so we'll know because glass as a

material is highly thermally conductive.

So if you can have a little bit of glass, it's poor performers.

If I have a lot of glass, it's still port with thermal performers.

Yeah.

It's a material property.

Yes.

Thicker glass has less heat transfer than thinner glass.

But not significantly so in the way that changing the material has,

so it's the, it's with the glass, it's the, the Lowe coating, the spacing, that's

really adding the value to spacer bars.

Like that's where performance is coming through.

And,

and so if you look at a window and say, you have a single pane

of glass, so how can I improve the performance of this glass?

Let's set aside the frame for a moment.

Then the first thing you do is look at the conduction across that.

Yeah.

So what do I do?

I could go double blazing.

And so what I'm trying to do then is to separate my two highly conductive

elements, glass on either side and trapped in between a, a volume of a gas, the

air, so in the usual or the easiest case.

And by trapping air, the conductance of air is much, much

lower than that of, of the glass.

And so I reduce the conductance across that buildup.

Yeah, it's the, the huge benefit you'll see in going to double players.

Now the next one is convection.

And so this again is an air mass that's holding heat energy transferring from

a warm space, so internally inside in winter to the outside, and it

carries that energy away, and that's not what we want to have happen.

Now, if we use that glass of buildup as a example of this for a second,

it's if you we accept that it's the air that's doing all the heavy lifting

in that double waste unit, then it would be intuitively reasonable to

say, well, why do we just build these with say, 10 mil gaps or 16 mil gaps?

Why don't we build them with 30 or 50 mil air gaps instead?

Shouldn't that perform better?

And in terms of conductance, yes, absolutely it is better, but the problem

there arises, so you get convection.

So you've got your interior surface of glass.

So again, we're thinking a warm heating dominated climate.

So it's warm that interior face of glass.

The exterior bit of glass is cold, and so the air that's trapped in that

cavity, when that gla and that air gets near to the cold surface on the

outside equals what does cool air do it?

It drops and then cycles.

It hits the glass on the inside, it goes warm, and you get exactly

what my mission do I to out.

It cycles around.

It moves Ed currents that this convection.

So when I do that, I've now got this air that's moving, and so the air is

carrying the heat energy from the interior face of glass towards the exterior.

It touches the exterior face of glass.

What does it do now?

It transfers by conduction the heat energy into the outside pane of glass, which

then conducts out towards the exterior.

Is your brain try.

No, it's not.

'cause it actually makes sort of sense.

Is it?

Because then, because then it makes sense now that um, when you start,

I guess talking about double verse triple glazed and cam please jump

in if I do this, say this wrong.

'cause you can have a triple glazed unit with external glass,

middle glass, internal glass.

And that might be overall 32 mil thick.

Right?

So I guess then ask the question, well why don't it still double glaze?

That's overall 32 mil thick.

But the reason is that you've got the convection that happens within that DGU

and you don't get that same impact in a triple glaze because that convection

is limited to a smaller space outside.

And then as you move through that wall, that bit of glass,

it's lessens on the inside.

My kind of spot on right up.

Yeah.

So, exactly.

So let's, if we just borrow, let's just say you can put a 24 mil egg out.

Yeah, in between a double glaze, if you now whack a third pane in the glass down

the middle and split that into two 12 mil gaps, you are, you've got the same total

air layer conductance 24 mil of air, but you've got two 12 mil gaps of air and you

don't get that convection falling as much.

So if you've got a tracked air void, depending on the temperature difference

inside and out, but in, certainly in the Australian climate, say, where

it gets to zero outside and maybe 20 degrees inside in a wind, then at

about 12 mil below a tracted air mass won't have much convection to it.

So, so am I hearing right?

And, and, and please Don, now fancy this with, well that depends.

Um, am I hearing right that there is like an optimal gap

between balance that depends?

It it does depend because it depends on the temperature difference.

And so it's really clum climatic.

And this is where we get so confused in the glass space.

Yeah.

Between different test standards.

Yeah.

So in Australia, you know, we probably shouldn't go down this rabbit hole

here, but in Australia we go to A FRC, which is adopted for an NFRC, the North

American Test standard, which uses very cold exterior air temperatures

when it's more than a 16 or something.

I can't re, I might have heard that wrong, but it's minus something far colder

than we would experience in almost all Australian climates and, and 20 degrees

say inside, when you have that very high delta tube, that temperature difference,

say 35 odd degrees, then even at minus gaps, sort of 12 to 14 mil, you'll drive

that conducted air movement more rapidly.

Whereas if you are, if it's only five degrees outside, plus five and 20

beers inside, then the tendency for that air to start convecting for those

I currents to form is far reduced.

And so you could still go for say, a 14 milli gap and not had significant

Yeah.

Can reference,

I wanna go back a little bit for a second though, because we're sitting

here talking about glazing and windows.

But windows are a form of insulation.

Yeah.

Obviously this, we just wanted to, I wanted, was just thinking

before there's potentially a whole podcast on talking about flash.

So while we're, while we're talking about insulation here.

What we're talking about I think is probably, uh, yeah, windows are formed,

insulation, we've got this big structure and all of a sudden they're cutting

a hole in it and it needs to perform as close to as we can in the walls.

It's pretty much where, yeah, just wanted to keep everyone on track of.

And so let's jump across insulation for a second.

So our standard insulation is our bulk insulation, our bat, you know,

the, the woven glass wool usually thing that we, we get from our

hardware or how is that working?

Well, it's glass firstly, and we've already established that

glass is highly conductive.

Yeah.

Can I just stop just for one second because, um, and I just, and I do just

wanna take it back to glass for a second.

And this is probably just sort of closing out that comment before

when you said conduction, convection and radiation is all relevant.

And if we, we've talked about conduction, talked about convection in glass.

Could, let's quickly talk about how radiation.

Is also um, a part of that glass unit.

This is one of my big gripes.

Yeah.

Is everybody talks about, oh look I've got double waste.

Fantastic.

But that's like saying, I've got a new car.

What did you get?

A Toyota Getting a car doesn't mean anything.

'cause the next question always ask 'cause what's sort of car?

Yeah.

There's a hell of a big difference in double glazing is exactly the same.

There's double glazing and then there's double glazing.

Yeah.

There's a huge difference.

And a lot of the di a part of the difference is the size of

that cavity we've talked about.

Forget about the thickness of the glass.

That's tertiary.

It doesn't matter.

Yes.

The how deep is the cavity.

Has that cavity got a noble gas like Argonne in it?

Because Argonne has less conductance than than hair.

And you contend to go through a deeper cavity with Argonne before

you get those ED counts for me

and the air is to be still because this is gonna lead to my second part.

And is and is that the reason why we have started to put.

Gases in there rather.

Okay, cool.

So just to slow that convection.

Uh, and the better can lower conductance of argonne versus air.

Okay.

So conduct.

Okay.

Yeah.

All right.

Now,

so, so adding a Argonne to AGL double glazed unit gives you a

improvement, you know, thrown around numbers, but maybe T cent.

No, it's, it's material and it's relatively cheap and easy to do,

and therefore we do it, but it's not massively changing performance.

They glas it.

Where you get the real benefit is going for those things we call

low ES Let's again, constraint on a he dominated climate.

We've got long wave of radiation coming from the sun.

So hot, hot, um, things.

The, the spectrum of heat energy generated tends to be longer

wave a longer a wavelength.

Yep.

So the sun obviously being massively hot.

Long wavelength.

It comes in, it strikes our bus, it gets towards an interior.

It warms our interior spaces in winter, which is just what we want to have happen.

And it heats our sofa and the floor and, and everything else.

And then those materials warm up, but nowhere in the air is hot as the sun

and they emit short wave radiation.

Is that, is, is that like a bit of a thermal mass thing?

Like is that what you were saying?

The furniture, because I've noticed in a house we just hand over, it's

beautiful and comfortable, but it seems to not, there's like an emptiness

of the heat, if that makes sense.

Yeah.

But until that, there was no furniture in his part yet.

So the house is just open, we're about to hand over.

When you go back there after it, it's the same, it feels

like there's more heat in it.

Well, depending on what the, the house is made from, by the time you add all of

those, the furniture stuff, that's gonna contribute massively to the thermal acid.

Yeah.

I, that's function, I think tons of stuff we put in L in, but, but we've got this

short wave radiation being admitted.

And then it goes back and it goes through that glass towards the exterior.

Now the low e coating is a spluttered surface of fancy material.

Silver is a collage component in it, and it's coated in your

heating dominated climate.

You'll be coated on surface free.

Now you count the glass surface from the exterior to the interior.

I was about to ask where, where does, does, does it matter where it is?

Yeah, so you've got, so one is the outside bit that gets hit by the rain surface.

Two is the inside of the outer pan.

So there's three, the one I'm talking about is on the outside of the inner pain.

Yeah.

So it's facing towards our tra air gap cap, and you put this spluttered

silver stuff on there and that reduces the emissivity of that surface.

So the radiation that can emit from that interior paned glass is

reduced to towards the exterior.

Can you please

explain what, and I don't even know how to say this.

That E in low EIF int, what does that

mean?

It's a material characteristic that is the rate at which electromagnetic

radiation can be emitted and be seen away from T material.

Okay, so different materials of different color?

Yeah.

Have different LA rates of emmi

and that low E works by it in summer.

It bounces the heat back in and in winter it kind of allows to come through.

So this is where I think low E gets really, really tricky and people get

confused because I think we inherently think of low E first as a solar control

glass, like something you will put on the house in the cans of Darwin, your,

our sole objective is to stop that spray and heat from the outside getting it.

And in that sort of climate you would put the low E coat on surface two.

So on the inside of the outer pain because you were trying to reduce the rate at

which that heat, that waxs the glass and then emit can radiate into the, the space.

But it's a different chemical composition you use because you tune it to try and

reduce the long wave of radiation because that's what's coming in from the sun.

So this is where, so I know this houses where the accidentally put

the gla in the wrong way around.

So it's very important then we that outside that stick our should

always be on the outside and you need to check your windows.

Yeah.

Yeah.

It depends.

It depends.

It kind of does because it also depends on the type of low eco

I whole bunch of other stuff.

Yeah.

But, but what's, what, rather than the, the, the sur the coat, the

surface onto which it's applied is the chemistry of that coating itself.

So where I think we really go wrong, it will, and this, to be fair, there

is just debate about this, but.

When you look up your glass specification or go your, your glass

manufacturer, they will have a, a suite of options for lowly coatings.

Mm. And some of those are designed for your very heating do or your

warm, sorry, your hop climates, your darlings and your cams.

And they are designed to reduce that long wave radiation into the space

and reduce the, the overheating.

If you are a Melbourne Hobart cradle mountain, then that's probably

not what you want other than two or three months of the year.

In the summer you've got the other eight months, a year when you want

to get that heat into the space.

And so then you use a different low coating that has different

characteristics to reduce the miss of the, uh, short wave radiation.

We typically put it on that surface three to try and improve the rate

of heat retention of that class.

Wicken, the space

are, are we talking about solar, heat and coefficient right now?

Correct.

Yep.

Okay.

SHGC.

Yes.

So, so there's two phrases.

There's S-H-H-G-C that we would use in words and what we use in Australia, A FRC.

And, and then in the European context we use a thing called igo Fair.

Similar but slightly different is, is solar and

coefficient represented as a number?

Yes.

And, and lower the better.

Am I right?

I thought it was the opposite to you.

Values

solar, heat gain, coefficient, or G

Yeah.

Are a coefficient.

So, so heat gain coefficient is represented as a G, is that, no, no.

No.

Or G. Or G. G. Value for pass.

Sorry.

Yeah, sorry.

G,

G value is the phrase or the acronym where you shopping.

European quota.

Yes.

Okay.

Yeah.

Um, which is actually easy to understand too, I find

Possibly, but both of them are coefficients.

They have a value from zero to one.

Yeah.

If, if the coefficient, the SHGC, let's just use that one, is one

that means all of the rodent.

People that just strikes that class.

It's penetrates through on the other side.

Yeah.

And that, and that's what you want if you are in a ate.

Yes.

Okay.

'cause you wanna bring, you wanna bring the heap in.

So which one have no low E You just want to have clear bias.

Yes.

Except

you wanna it the other way around.

You want it to bounce back in.

Just to remind everyone right now, we are, we're currently talking about radiation.

Yes.

But currently it's where radiations.

And so, so we've established that ans HDC value one means all the radiant heat

comes through a value of zero intuitively meets, none of it comes through.

And so green lanes, you want it as close to one as possible.

In Cairns, you want it as close to zero as possible.

Now in reality, you can't get either of those extreme values and most of your,

and this again, depends on how you, whether it's singles level or triple ways.

But your SHGC, you know.

Heating dominant liner, say Canberra Mellon.

Hobar tends to have an SHC something in the 0.5 to 0.6, 5.7.

And whereas in Cairns it'll be closer to 0.3.

And does your solar heat and coefficient change?

And I think under the answer to this, from single to double, to

triple to whether you've got low E to whether you've got, yeah.

So so that's where it's it's actual, it's looking at the entire unit.

That's right.

What?

It's a glass.

He's not glass.

No.

Yeah, that, that, that's right.

These glass is, and these low E coats are not usually visible to the naked eye,

except maybe on the certain angle, or

this is definitely not too far.

If you've said a comment before that air is a great insulator, uh, foot glazing.

And I then wanna now quickly move that to a conversation about ventilator

cavities because we have an air gap.

Does that mean the air in the ventilator cavities is also brand insulator?

No.

Could f.

And so, which means a convection is happen at a very fast rate.

Uh, uh, you are, depending on how you do it, you are des hopefully

designing that ventilator cavity to be just that ventilated.

You wanted ventilated because you wanna carry away moisture and help

drying of the, of the assembly.

And so doing that, inherently you are gonna be taking any

heat energy in that cavity.

And trucking next door is the outside.

Yes.

So we, it offers almost zero, uh, heat retention of heat, uh, benefits.

So then when we have this metal sarp thing, as people would say, it's the

insulation, it's a radiant barrier because that's the, it needs that air gap though.

Is it actually insulating?

Yeah.

Okay.

So, so it comes back to a couple of things here.

So still air gaps.

Yeah.

Yeah.

So, so a is a shiny surface has a, a, a much, uh.

Lower sensitivity Yeah.

Than a, the, a matte dark color surface.

And so the idea is it reflects that heat away, which is obviously

desirable in a, in a hot climate.

Uh, if you want to get the optimum performance out of that foil or that shiny

surface, though, you need two things.

Firstly, you need to keep it shiny.

And if you are putting it on a flat roof and you're not gonna

see it for the next 50 years, it's unlikely to remain shy if there,

oh, I just was at a house doing the inspection last week and you, it is

kind of exposed when we went up to attic and it's always brought it away.

And then secondly, you need a still bag gap adjacent.

And usually we're putting these falls on the outside of

our star frame in no egg gap.

And there is still cavity's no egg gap.

Well, and if we do have a cav, a cavity in the dust worlds,

it's no longer a still egg gap.

And so the as built.

Performance of that assembly is significantly different to what you and

might test in a lab where you have a steel air extra, a clean set sheet of fault.

So you could say these metal sightings are a scam.

I, I, in in, in a housing environment, in, in a, in a lab.

It works.

Oh, in a house it wouldn't, yeah.

I'm certainly

not

gonna say there're scare.

Can I, can I also point out too that, um, this probably also pokes a couple

of holes in our star ratings as well, because a, a lot of the time the

star rating includes your 1.5 r, 1.5 anticon, which sits on top of your

batten claddings, your roof claddings.

And if you then got that ventilator cavity underneath that's moving,

you can't then include that R value in your overall R value.

But, but Hurs does do that.

Yeah.

And, and again, this is one of those, it depends on because ventilated as

well, this is all brief and from an insulation point of view, you don't

want to ventilate that caver at all.

But from a moisture point of view, you absolutely do want to ventilate that.

So where does the balance lie?

Yeah.

And assuming as I think we would all agree with on durable weldings that don't ride

out in five years, then we urge towards, we've gotta do with moisture first.

Bugger the energy.

Yeah.

And so you ventilate the space, in which case the thermal benefit of that

for faced, uh, uh, blankets sitting up on the top of the roof truss is

massively declined in a, in, in a heat transfer towards the exterior context

with that risk of going too much standard like a tangent.

So in that ventilator cavity, what we're seeing is convection.

Is that right?

It depends.

Or, or, or like

you are also seeing radiation, but predominantly that'll be convection.

Yeah.

Okay.

So then if we're thinking about that, how we explain that scenario

in a double glazed unit, does that impact that convection?

And I'm thinking about like the size of the cavity year.

Does that then impact how the insulation performs inside, like underneath that WIB?

Or is it not impacted by the convection that's sitting on top?

What we didn't say at the outset is the insulation is all about still air gaps.

Yes.

That's all we're trying to do is achieve a still air gap because air is a really

excellent insulator if we maintain small pockets of air that can allow convection.

So you to our,

sorry, what's a maximum?

Maybe like 20, 22 mil?

It depends.

It depends on temperature difference.

Yeah.

Yeah.

And so, you know, an Australian climate where we don't tend to have minus 20

temperatures outside the Dells are tea.

The difference between the inside and the outside temperature on a hot day or a

cold day is probably less than 20 degrees.

Yeah.

You know, it's 40 degrees outside, 25 inside.

We're at zero out and 20.

Yeah.

And so the ability for that air to convect is somewhat reduced and if

temperature difference was larger.

But what we are fundamentally trying to do is create lots of tiny little pockets

of air in our glassful, or in our fo now XPSE, P-S-P-I-R, whatever material links.

Lots of tiny, little trapped

Yeah.

Voids of air.

We, we had a, a situation recently on a project where

we're, um, working on together.

We, we had a C cavity and then the, the art, like the bats were only

gonna take up to, there was about 20 mil at the top of that where, um,

there was gonna be a void because the bats didn't quite fill the void.

And I just thought, oh, beautiful.

Um, there's trapped down there.

And you, I'll, I'll let you kind of finish off where we got to with this one

because I learned something that day.

So the issue we grew, I think is sort of a, a, a halfway house if,

if I have a trapped air void towards the cold side of a construction.

Yep.

So imagine, say a roof truss construction where I run my

insulation of the ceiling fine.

And then I have a void above before I get to my, my socking.

And then yeah, my outside.

I had this trapped mass of coal air in the woods, period.

And that's a, a big depth so far, more than 12 or 40 mil.

So you, there's a chance that you end convection and that air will move and

any moisture that gets up into that space can then be picked up by those

e currents and carried around in ways that're not entirely predictable.

So when we build our, we build, so itlo cavity, batten plaster,

is that air gap still still?

If we didn't put in installation, like how still is it?

So, so that's because on the inside it's not running, so,

so let's assume you're putting a 35 on button.

Yeah.

Pretty typical.

Yeah, probably.

Um, that, that will have some air movement, but not much because there's

not a big delta t it's only once you get into where the insulation is between

your in or your external grab that you, you have a temperature difference.

Yeah.

And, and a risk of convection for,

so when you're doing the PHBP, do you allow that, if there's no insulation in

zone, do you put a value in there still?

So if you've gone be conservative, you've given no value?

Yeah.

Um, we would normally give it a value because it is, as you say,

essentially a still a, yeah.

Yeah.

So what Mel was saying before there, there's probably, there's

less risk on the warm side.

And in our scenario there was a higher risk because there was

quite a potential of a drastic.

Temperature differential from the inside to the outside because we had a

significant amount of the insulation.

It was like R four or something?

Yes, on the warm side.

So if you think, again, zero degrees outside, 20 degrees inside.

If I've got R four of insulation, by the time I get to the outside face that I'm

getting pretty cold, if I then put, say a photo face blanket a palat, which is a 1.5

ish, then I've, I've already reduced, you know, a good two thirds of my temperature.

So I've gone from 20 degrees on the top side of that R four installation.

I'm now maybe around 12 or less degrees and that almost certainly below dew point.

Yeah.

And so I've got this trapped massive of cold air that possibly is gonna

vec and there is a chance that I'm gonna have moisture issues.

So prevent, even though that we, we probably did in some areas,

compress the insulation a little bit.

The risk was, well, the benefit of that is that, that we

weren't allowing any end move.

That in summary,

that's, that's right.

So your glass wall is of a sufficient density.

Yeah.

That you are trying to restrict the ability for convection air

movement through that material.

Yeah.

Now that doesn't mean if you've got pressure difference in and out, obviously

glassful is not an air tightness.

You know, you can get ahead on one side and you'll feel and

blowing through the other side.

That's not what we're talking about here.

It's the temperature driven air movement.

So delta C across that glass, is it gonna drive those ed currents in that, the

con And that's conviction.