I thought this video would explain how you can have "breathability" to stop the buildup of CO2 in an airtight home. It seems to be more about moisture (important, but not the same thing). How can you justify creating airtight homes that just build up CO2? Is the only way around to install expensive air filtration systems?
There are 3 options, operate your windows, install a push pull ventilation system, or retrofit something to your existing ducted system. Relying on leaks from mouldy wall cavities is not a good source of fresh air.
How does an "airtight" layer allow through moisture vapour. Isn't moisture vapour H2O molecules just like CO2, O2 etc ? Why does one go through and not the others ? Unless H2O molecules are unusually small ?
Basically everything is permeable to air and water vapour to some extent. You're right. They're all just gases - H20 is like 02 and N2 and CO2. They pass through, just slowly. But we're talking about major differences in scale here. A material leaks air (N2 and O2) slow enough for someone to declare it's an "air barrier" and it leaks water vapour fast enough for someone to call it "vapour permeable". Same thing, just different ways of talking about it and different uses. For me to talk about air permeance and vapour permeance in the same units of measurement (m3/hr/Pa/m2) or (MN*s/g) would be sort of useless to you and they're very hard to measure in the same way. Sean Maxwell - Pro Clima Australia
In simple term, let's look at the process like this: The moisture in the wet side is first 'absorbed' by the material, then the drying potential of the outside (dry side) air will begin to suck the moisture out just like how laundry is dried by airing. This process occurs not only in vapour permeable membrane but also common building materials such as plasterboard (drywall). One very common example that most of us would have got our hands on is the "Gore-tex" fabric for windbreakers and activewear.
The temperature on both sides is different and is changing all the time so the time periods of "balance" are very short. When there is a balance, then no moisture transfer takes place. It is more correct to talk about the constant moisture transfer to achieve the balance. Breathable walls (those that allow moisture transfer) are actually air tight. Take an ordinary 450 mm masonry wall and try to get any air through it. You will see really low numbers. Usually it is different interfaces (with windows, beams, doors) that are not airtight. The question is about sustainability of this airtight material that you are using. Can it last 200 or 500 years? Masonry walls can easily last that much. Changing your airtight layer every 50 years along with changing all rusting reinforced concrete every 50-100 years is simply not sustainable for the planet. It is a fast food style construction that does not last. If you are interested in making money, then sure go for the fast food architecture that will damage environment and will leave no legacy and traces in 100 years because the expected life time of such houses is kind of low.
Good video guys! Hear this one all the time in the States too.
Matt Risinger Fair dinkum! It’s an outrage. 😉
I thought this video would explain how you can have "breathability" to stop the buildup of CO2 in an airtight home. It seems to be more about moisture (important, but not the same thing). How can you justify creating airtight homes that just build up CO2? Is the only way around to install expensive air filtration systems?
There are 3 options, operate your windows, install a push pull ventilation system, or retrofit something to your existing ducted system. Relying on leaks from mouldy wall cavities is not a good source of fresh air.
How does an "airtight" layer allow through moisture vapour. Isn't moisture vapour H2O molecules just like CO2, O2 etc ? Why does one go through and not the others ? Unless H2O molecules are unusually small ?
Basically everything is permeable to air and water vapour to some extent. You're right. They're all just gases - H20 is like 02 and N2 and CO2. They pass through, just slowly. But we're talking about major differences in scale here. A material leaks air (N2 and O2) slow enough for someone to declare it's an "air barrier" and it leaks water vapour fast enough for someone to call it "vapour permeable". Same thing, just different ways of talking about it and different uses. For me to talk about air permeance and vapour permeance in the same units of measurement (m3/hr/Pa/m2) or (MN*s/g) would be sort of useless to you and they're very hard to measure in the same way.
Sean Maxwell - Pro Clima Australia
In simple term, let's look at the process like this: The moisture in the wet side is first 'absorbed' by the material, then the drying potential of the outside (dry side) air will begin to suck the moisture out just like how laundry is dried by airing. This process occurs not only in vapour permeable membrane but also common building materials such as plasterboard (drywall).
One very common example that most of us would have got our hands on is the "Gore-tex" fabric for windbreakers and activewear.
This is a very good question, answered well.
The temperature on both sides is different and is changing all the time so the time periods of "balance" are very short. When there is a balance, then no moisture transfer takes place. It is more correct to talk about the constant moisture transfer to achieve the balance. Breathable walls (those that allow moisture transfer) are actually air tight. Take an ordinary 450 mm masonry wall and try to get any air through it. You will see really low numbers. Usually it is different interfaces (with windows, beams, doors) that are not airtight.
The question is about sustainability of this airtight material that you are using. Can it last 200 or 500 years? Masonry walls can easily last that much. Changing your airtight layer every 50 years along with changing all rusting reinforced concrete every 50-100 years is simply not sustainable for the planet. It is a fast food style construction that does not last. If you are interested in making money, then sure go for the fast food architecture that will damage environment and will leave no legacy and traces in 100 years because the expected life time of such houses is kind of low.