Should the walls breathe?

Do I need a vapor barrier on the walls of the house and should the walls “breathe”?

On the breath of the walls constantly write and tell the sellers of building materials trying to convince customers to buy their goods.

We will try to figure out whether the walls need to "breathe."

First, what is breath?

Breathing is a process of drawing in and releasing air by the lungs during which living organisms absorb oxygen and release carbon dioxide.

As is known from the practice of the wall, clearly are not living organisms. Therefore, the term “breath” to apply to the walls is not entirely correct.

What actually happens to the walls during the operation of the structure?

Most wall materials, except metal, plastic and solid concrete, can pass air and water vapor through them.

Is it good?

Consider the following situation. Winter is cold outside, and the rooms, respectively, should be warm. In residential areas, water vapor is present in the air. It is distinguished by people both in the process of their vital activity and during household processes (cooking, washing, wet cleaning, etc.). Air with water vapor penetrates wall structures and cools. When this occurs, condensation of water vapor, which turns into water droplets. The place in the wall where the steam turns into water is called the “dew point”.

точкой росы

Those. from the side of the street, part of the wall is soaked with moisture and no longer takes part in protecting the premises from the cold. They say about it: “The wall is frozen”.

During the winter, the dew point moves towards the warm room and the insulating properties of the wall are reduced.

теплоизоляционные свойства стены уменьшаются

In summer, the moisture dries out and the wall becomes uniform in its thermal insulation properties.

It should be noted that the outer surface of the wall is often lined with insulation, covered with a decorative finish or plaster which in turn prevents the walls from drying out.

The more pores in the material, the more air there is and the warmer it is. But at the same time with that large amount of water it can be saturated.

Therefore, it is not correct to call the “breath” of the wall an advantage.

What to do?

If we want to achieve maximum thermal insulation properties, then our task is not to let water vapor into the body of the wall. To do this, the inner surface of the walls should be covered with a layer of vapor barrier.

So in the frame houses the use of vapor barrier is mandatory, since without a vapor barrier the frame house can simply rot. As the vapor barrier used plastic film.

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In houses of brick, ceramic blocks or aerated concrete, the absence of vapor barrier does not lead to visible trouble. True, when the walls freeze up, heating costs increase, but since the walls did not fall and the fungus did not appear, it seems that everything is normal.

How to reduce the vapor permeability of walls of ceramic or aerated concrete blocks?

Apply the film will not work. On the plastic film just does not hold plaster. But the problem of reducing the vapor permeability of the walls of porous materials remains.

To solve the problem, the inner surface of the wall must be impregnated with a primer in 2-3 layers and apply a layer of cement plaster.

I emphasize, namely cement plaster, because plaster mixes are porous and perfectly pass water vapor.

For the final finishing, you should use materials that do not allow water vapor, for example vinyl wallcovering.

After reading the last phrase, many will think - horror, the house turns into a thermos, but what about the breath of the walls?

And indeed, our task as much as possible to turn the house into a thermos. And for ventilation, use not walls, but ventilation ducts, recuperators or, in extreme cases, window leaves.

Summing up, I will express the pardox thought that the “breathing” of the walls is not an advantage, but rather a lack of construction. And in the house-thermos with a ventilation system is not a disadvantage, but an advantage.

And in addition: through the walls in the house takes 25% of the heat, through the ceiling and the roof - 30%, through the ventilation system - 20%.

Keep warm - build right!