I received an explanation from a construction engineer who mentioned that in a house we were working on, the uncontrolled ventilation, i.e., through gaps, etc., should correspond to a maximum of one 100 vent over more than 200 sqm. Now, not all of this is on the vapor barrier, but the tighter it is, the better...
Another tip is to cut small holes in the plastic and press the plastic over boxes, etc.
/Kent
Another tip is to cut small holes in the plastic and press the plastic over boxes, etc.
/Kent
The actual ventilation through penetration holes in a vapor barrier is often not the greatest risk with leaky penetrations.snickarboden said:
The idea of the vapor barrier is to prevent moisture from forming on interior materials due to the temperature differences on both sides of the vapor barrier. In cases where moisture forms and a vapor barrier is needed, condensation can collect on the vapor barrier. If it's leaky, you risk a dripping point where the hole is, which can focus disproportionately much water through the hole. This results in the materials on the inside getting more concentrated moisture than they would without the vapor barrier.
--- Mats ---
Of course, I probably expressed myself a bit poorly there but took an example to show how closely one sometimes wants things. That the primary function of the vapor barrier is not to control ventilation is quite clear, and likewise, as you write, that it can become problematic if there's too much water where the vapor barrier is not tight.
Then the problem becomes that ventilation and vapor barrier are somewhat linked, so the tighter you build, the more you need to ensure you have well-functioning ventilation, which is not easy to solve.
/Kent
Then the problem becomes that ventilation and vapor barrier are somewhat linked, so the tighter you build, the more you need to ensure you have well-functioning ventilation, which is not easy to solve.
/Kent
OK, but then one should focus on sealing all wet areas, where there is occasionally warm humid air. My electrical panel will be in the laundry room so one must be careful with the fabric there. maybe foam the bundle with electrical conduits.....
/C
/C
I'm not sure I buy that, do you mean there would be such amounts of moisture that it runs along the vapor barrier? And do you mean that this moisture would mainly be on the outside of the vapor barrier and you want to prevent it from getting in? If you ever get condensation so that it runs along the moisture barrier, you have very serious problems with the house, this basically doesn't happen. And if it did, the condensation would end up on the inside of the moisture barrier, not the outside. Without exception. But maybe I'm misunderstanding what you're writing?Mats Bengtsson said:
The important thing about having it tight is that you don't want moist air to get out into the construction if the pressure is higher indoors than outdoors. Then you get an airflow, convection, that can cause increased moisture levels further out in the construction.
Cacas>Remember that in wet areas there is a vapour barrier in the form of a waterproofing layer.
/Kent
/Kent
Hi, Yes, you understand what I'm writing (we can then discuss whether I'm right, so here's more text). As usual, a house built for a vapor barrier, with forced ventilation, and with deliberately reduced indoor pressure is not particularly sensitive to the problems.jon_h said:
One must distinguish between two things, moisture diffusion and moisture convection. Moisture diffusion is moisture that drives out through the wall//weather barrier/… This is the problem you want to prevent with a vapor barrier, which allows very little moisture diffusion. What you're describing with condensation on the inside of the vapor barrier applies only as long as the vapor barrier is tight (not in terms of diffusion but in terms of holes), and as long as we assume the air is more humid inside than outside (the exception is in summer in regular houses and a larger part of the year in less heated summer houses or sheds).
What I'm talking about are two different problems, partly what's called moisture convection, caused by a hole in the vapor barrier which otherwise is diffusion-tight, with overpressure from the inside and with the humid air inside the house. Additionally, problems that arise with reduced pressure from the inside and with the humid air outside (when it starts to get warm outside, and where for some reason one does not maintain a higher temperature inside than outside (outbuildings, sheds, and roofs in regular houses in the summer)).
If there are spots with holes in the vapor barrier, you risk in the first case getting moisture convection, and the problems around moisture convection are at their worst when we talk about small holes in the vapor barrier. Air convection drives up the humidity outside the vapor barrier and can cause rot. This can, in connection with indoor overpressure, create very large problems, which is why discussions about not combining moisture barriers and houses based on natural ventilation are very important.
In the second case, you risk getting moisture accumulations on the outside of the vapor barrier, which depending on how the vapor barrier has been made, can cause moisture problems both outside and inside the moisture barrier if there are holes in the moisture barrier.
--- Mats ----
I clearly understand the difference between diffusion and convection, but I still don't understand how condensation could occur on the outside of the vapor barrier in a heated house? Or do you mean that the humidity level can generally increase in the wall if moist air is allowed to pass through the vapor barrier and then condense in the wall? In that case, I understand and agree.
Yes, one half of my argument concerns the reason you describe, so we can then consider that clear.jon_h said:
But I have an addition to that. There is a frequent discussion about whether or not one should always use a vapor barrier, where factors such as how much you heat and how the house is built, ... affect the arguments.
My claim is that there are situations when the most humid air is on the outside. These occur especially when it is warm outside. In that situation, it may be that the inside of the house is the cold surface (especially when you start using air conditioning, but if you choose not to heat the house more than slightly, it can occur even more often in the spring and autumn). Then you also risk condensation, and that will occur on the outside of the vapor barrier.
--- Mats ---
That's exactly right, and it's a problem if you have a vapor barrier in summer houses and similar buildings that remain unheated. But in a regular villa, condensation does not occur on the outside of the vapor barrier, even if it is unusually warm and humid outside. If outdoor air were to condense against a surface that maintains perhaps 22-23 degrees (which could reasonably be the temperature of the vapor barrier), it would cause condensation on walls and ceilings indoors if you ventilated a little. We don't have such extreme humidity conditions. Furthermore, you would have quite serious damage to the house if it were as you described, especially with a completely tight vapor barrier.
No, it's lucky we don't live in Texas. There, they apparently recommend a vapor barrier on both the outside and inside:jon_h said:
Where humidity is high in the summer and air conditioning is used, a vapor barrier is recommended on the exterior wall (warm side). During the winter, the interior vapor barrier prevents water vapor from penetrating the insulation and condensing on a cold surface. During the summer, the exterior vapor barrier can prevent water vapor from penetrating the insulation from the outside and condensing on a cold air conditioned surface on the inside of the wall.