How does an unsealed vapor barrier work in houses with exhaust ventilation? I've read that what happens is that moist indoor air escapes into the outer wall where it cools down and causes moisture damage. At the same time, outdoor air leaks in, reducing energy efficiency...
I, who don't know everything about the laws of physics, am a bit puzzled as to how the moist indoor air escapes through the gap, while outdoor air comes in, when there is negative pressure in the house.
Anyone have time to explain?
I, who don't know everything about the laws of physics, am a bit puzzled as to how the moist indoor air escapes through the gap, while outdoor air comes in, when there is negative pressure in the house.
Anyone have time to explain?
Know-It-All
· Västra Götaland
· 11 967 posts
As long as you have undertryck, there is no major danger. Read this text and you'll probably understand.
https://www.sp.se/sv/index/services/moist/general/Sidor/default.aspx
https://www.sp.se/sv/index/services/moist/general/Sidor/default.aspx
The risk of moisture problems is significantly reduced if there is a controlled negative pressure. On the other hand, there is a risk that gases and odors from insulation and other building materials can be drawn into the home. Whether this is a big problem or not, I will leave unsaid...
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It is often the case that the house as a whole has negative pressure, but locally there can be positive pressure due to thermal forces. The simplest example to illustrate this is a 1 1/2-story house with exhaust air taken from the ground floor where the kitchen and bathroom are often located. On cold winter days, this results in positive pressure on the upper floor and negative pressure on the lower floor, as it becomes easier for the exhaust air to draw air from the supply vents than from the upper floor. Then warm, moist air can seep into the insulation despite the negative pressure on the ground floor.