Hello everyone,
I often read about the concept of "breathing walls."
Statements like:
- "We were told not to insulate because otherwise my 31cm (12 inch) brick wall won’t be able to breathe anymore."
- "We don’t need a ventilation system; the timber frame wall has no membrane, so it can breathe well."
- "We have a vapor-permeable wall, so moisture can escape outside, and I don’t need a ventilation system."
- "The wall is vapor-permeable, a ventilation system is not necessary, and you basically don’t need to ventilate."
I keep seeing these and similar sentences online and have even heard them personally from house building companies—the latest just this Monday. Other opinions include: Don’t put photovoltaics on the roof due to too much electromagnetic pollution. He would never install a ventilation system. Climate change? That doesn’t even exist. At some point, I just got up and left.
I’m an engineer, not involved in house building. But in my opinion, these statements make no sense at all.
A wall can never really "breathe" properly.
Here, "breathing" means a significant moisture exchange.
How is this supposed to work physically? It’s not a thin membrane, but a thick, solid wall or one filled with insulation.
Sure, a certain amount of moisture transfer always occurs. But in my view, this is absolutely negligible. There is no way that the few liters of moisture produced daily in a single-family house could pass through the wall to the outside without either a ventilation system or manual ventilation. Physically, this just can’t happen.
Of course, it’s different with older houses. They have numerous leaks that allow air and moisture exchange. But modern houses are sealed tightly. Therefore, there is no real air exchange through the walls.
And beyond the aspect of "removing moisture to the outside," there is also the aspect of "bringing fresh air into the house."
My point is not to argue for or against ventilation systems. I am in favor, but it can also work without one if you don’t want it—just with regular manual airing, in my opinion.
What do you think? Do these "breathing walls" really exist?
Am I completely wrong? Or is this myth just incredibly persistent among home builders and even building companies?
Best regards,
Specki
I often read about the concept of "breathing walls."
Statements like:
- "We were told not to insulate because otherwise my 31cm (12 inch) brick wall won’t be able to breathe anymore."
- "We don’t need a ventilation system; the timber frame wall has no membrane, so it can breathe well."
- "We have a vapor-permeable wall, so moisture can escape outside, and I don’t need a ventilation system."
- "The wall is vapor-permeable, a ventilation system is not necessary, and you basically don’t need to ventilate."
I keep seeing these and similar sentences online and have even heard them personally from house building companies—the latest just this Monday. Other opinions include: Don’t put photovoltaics on the roof due to too much electromagnetic pollution. He would never install a ventilation system. Climate change? That doesn’t even exist. At some point, I just got up and left.
I’m an engineer, not involved in house building. But in my opinion, these statements make no sense at all.
A wall can never really "breathe" properly.
Here, "breathing" means a significant moisture exchange.
How is this supposed to work physically? It’s not a thin membrane, but a thick, solid wall or one filled with insulation.
Sure, a certain amount of moisture transfer always occurs. But in my view, this is absolutely negligible. There is no way that the few liters of moisture produced daily in a single-family house could pass through the wall to the outside without either a ventilation system or manual ventilation. Physically, this just can’t happen.
Of course, it’s different with older houses. They have numerous leaks that allow air and moisture exchange. But modern houses are sealed tightly. Therefore, there is no real air exchange through the walls.
And beyond the aspect of "removing moisture to the outside," there is also the aspect of "bringing fresh air into the house."
My point is not to argue for or against ventilation systems. I am in favor, but it can also work without one if you don’t want it—just with regular manual airing, in my opinion.
What do you think? Do these "breathing walls" really exist?
Am I completely wrong? Or is this myth just incredibly persistent among home builders and even building companies?
Best regards,
Specki
There are basically two ways for moisture to leave a house:
- Convection
- Diffusion
The amount of moisture that can pass through a diffusion-open wall by diffusion is many times lower than the amount that passes by convection (in an older building that is not airtight). A modern solid wood wall can therefore be diffusion-open but is (or should be) airtight by design.
- Convection
- Diffusion
The amount of moisture that can pass through a diffusion-open wall by diffusion is many times lower than the amount that passes by convection (in an older building that is not airtight). A modern solid wood wall can therefore be diffusion-open but is (or should be) airtight by design.
S
Selbstbau6 Mar 2020 10:21We built a solid brick house with 17/18 cm (7 inches) walls WITHOUT a ventilation system. After about two years, we have no issues with mold or moisture. HOWEVER, the house must be ventilated from time to time!
Although we have a "breathable wall structure" (pure lime plaster and a brick ceiling), I understand this more as a system that somewhat (to a small extent) temporarily stores moisture and then releases it again. This moisture can only be removed through the windows to the outside.
If I were to build again, I would include a ventilation system. Not because of moisture—which we have under control—but simply for the comfort of always having fresh air inside the house.
Although we have a "breathable wall structure" (pure lime plaster and a brick ceiling), I understand this more as a system that somewhat (to a small extent) temporarily stores moisture and then releases it again. This moisture can only be removed through the windows to the outside.
If I were to build again, I would include a ventilation system. Not because of moisture—which we have under control—but simply for the comfort of always having fresh air inside the house.
T
T_im_Norden6 Mar 2020 10:21They refer to the ability of wood to absorb and release moisture.
In summer, the wood should store moisture, and in winter, when moisture is lost through ventilation, it should release it again.
It is similar to clay plaster, which is also supposed to be able to absorb moisture.
In summer, the wood should store moisture, and in winter, when moisture is lost through ventilation, it should release it again.
It is similar to clay plaster, which is also supposed to be able to absorb moisture.
H
hampshire6 Mar 2020 10:27The concept of the “breathable wall” dates back over 100 years to an attempt to measure the air exchange rate in houses. After sealing all gaps and leaks (allegedly), the air exchange rate did not change as previously calculated. The interpretation of this phenomenon—that the walls therefore "breathe"—is simply incorrect. Factors such as an unsealed stove were not taken into account in the calculation. Calling this a “breathable wall” is mostly a marketing term.
Tobibi schrieb:There are rooms where people prefer to spend time more than others. Some feel stuffy, others oppressive, while some feel fresh. It is undisputed that people react differently to various room conditions, and in hot weather, a tightly sealed wooden box will feel different from a plastic container. The air volume in a room also plays a role in comfort. How someone describes it is usually not very scientific. A house only smells bad if the air exchange rate is too low and/or if there are odor-emitting materials inside. Sometimes it’s just a new floor covering made from low-quality materials—and even a plastic container will smell different after years than a piece of wood.
I already find statements like “the climate was fantastic” in the previous post difficult. What exactly was so fantastic, or do other houses just smell bad?
nordanney schrieb:Both types of walls—if not covered with some kind of sealant—would be able to participate in the humidity balance of the room. Neither wall would do this if coated inside with latex paint. So, there are differences in the wall construction. To reduce this solely to the load-bearing material is certainly too simplistic.
Just explain to us why a wooden wall is climate-regulating compared to a solid wall.
H
hampshire6 Mar 2020 10:34Addendum: If you want to ensure a comfortable stay in your home, it is advisable not to use materials that have an unpleasant odor.
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