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
hampshire schrieb:
Some things are just easier than they seem: Just open the windows from time to time.You're not allowed to do that in an energy-efficient house *sarcasm* I can’t hear that argument anymore.
Since breathable roofs allow moisture to escape, I also believe that there are wall constructions that breathe. Why not? If the sd value decreases from inside to outside, it should not pose a physical problem.
I am not so sure about stone houses, but the phenomenon of visible stones through the exterior plaster, in my opinion, supports the theory that moisture is drawn out from the inside.
I am not so sure about stone houses, but the phenomenon of visible stones through the exterior plaster, in my opinion, supports the theory that moisture is drawn out from the inside.
N
nordanney6 Mar 2020 12:07Bookstar schrieb:
Since diffusion-open roofs can breathe, I also believe there are wall assemblies that can breathe. Why not? If the vapor diffusion (sd) value decreases from the inside to the outside, this should pose no physical problem.
I’m not so sure about stone houses, but the phenomenon of visible stones through the exterior plaster suggests, in my opinion, that moisture is being transported outwards from the inside.And how much water takes how much time to pass through the entire construction? And how much water does the house breathe in through the walls? It certainly won’t be a one-way street.Here are some quotes from online sources that anyone can verify and research:
It is true that many porous building materials, according to Pettenkofer, are air-permeable. However, air movement through the porous structure can only be initiated by a difference in air pressure between the two sides of a wall. Since the air pressure inside a building usually differs very little from outside air pressure, there is no driving force for such transport to occur.
Every building material reaches a moisture equilibrium with its surroundings. Depending on where it is located, a moisture balance and typical moisture content are established in the component. A component is in moisture equilibrium with the vapor content of indoor and outdoor air. In winter, outside air is very dry (30% relative humidity), while indoor air is more humid (around 30–60% relative humidity). The movement of water vapor molecules is based on their temperature-related kinetic energy and the concentration gradient from inside to outside.
In a typical household, about 5 to 10 liters of water per day are released as water vapor through breathing, transpiration (from people and indoor plants), cooking, etc. Only about 1–3% of that water vapor can be removed by diffusion through the walls, as all building materials offer resistance to diffusion.
Moisture production in living spaces varies greatly, for example when cooking, showering, sleeping, etc. Occasional high indoor humidity peaks, with condensation forming on cooler spots like thermal bridges or frost patterns (“ice flowers”) on poorly insulated windows, are prevented or reduced by water vapor sorption in all hygroscopic interior finishes of building components (plaster, wood-based panels, fiberboards). Sorption is a natural property of all mineral building materials and lacks a driving mechanism. The absorbed moisture is released back to the indoor air when humidity levels drop again due to cooking, bathing, etc. This moisture must be ventilated out. There is no alternative to active ventilation.
Typically, wall surfaces are not the only sorptive surfaces in a room. Textiles such as carpets, curtains, or upholstered furniture usually have even greater sorption capacity than wall materials and provide large surface areas. Unfinished wooden furnishings can also contribute somewhat to sorption. However, even in this case, moisture equilibrium is established within the closed system. Moisture can only be removed by ventilating with drier air. When this happens, humidity peaks in living areas are brief, so sorbed moisture has little time to deeply penetrate the walls before being released again.
Effective moisture buffering also requires adequate capacity to release the stored moisture. With regular heavy moisture exposure, for example in bathrooms, a “breathable” wall surface may be disadvantageous if it absorbs moisture and appears dry, leading to insufficient ventilation for drying and resulting in mold growth over time. In such cases, a surface that is neither “breathable” nor absorbent (such as tiles) is safer, as condensation is clearly visible, making the need to ventilate obvious.
nordanney schrieb:
And how much water takes how much time to pass through the entire assembly? And how much water does the house absorb through the walls? It’s not going to be one-way traffic after all.
Here are a few quotes from the internet that anyone can verify and look up:
there are tons of links inside. Always copy and paste them first into Notepad, it breaks all of them otherwise. Hurry up when editing.
Specki schrieb:
A wall can never really “breathe.”
Here, breathing means a significant exchange of moisture. I understand breathing as an exchange of air; I only let water out when I pee.
Apart from the fact that apparently one forgets physics as soon as one becomes Chancellor: if climate goals were taken seriously, conferences would take place via videoconference instead of producing countless hours of flights. What ultimately needs to be implemented has nothing to do with common sense—so looking for it there won’t lead to enlightenment. Politics relies on expert advice, and experts constantly make mistakes; otherwise, they would be true professionals.
In my kitchen, the wall actually breathes, but only at one single spot (where the pantry used to be separated, there is still an air brick installed). However, that does not replace ventilating, as a single fish roast without opening a window clearly proves to any layperson.
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