The difference of the partial pressure, and what it does with the roof at home

PA previous article on my blog vapor barrier error has caused a lot of questions of subscribers (link to it, I the ladies at the end), so I decided to continue the story of the roof of the topic of "thermal processes insulated roof. "

ANDso insulated roof 24/7/365 is in difficult weather conditions: from the outside it is exposed to rain, hail and snow, exposed to wind loads and even gets a dose of solar radiation.

BUT inside the roof influenced by water vapor, temperature variations and humidity. In general, the factors that can spoil the roof, a lot!

The difference of the partial pressure of water vaporinside and outside the house - the one factor that leads to a constant movement of moisture through the layers of insulation.

Inthis movement, there are two mechanisms:
- convective transfer pair
- and vapor diffusion.

ANDof these the most important is the first. It is through damage (holes, cuts) of the roof vapor barrier, which often occur during installation and use.

The first way to reduce the penetration of moisture from the room into the body of insulation -

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the use of dense and durable materials vapor barrier.
The second condition - neat installation (A lot of holes left right after installation).

That the partial pressure of making a roof?

In Russia, the biggest difference is the temperature of the air inside the house and outside in the winter is achieved. Accordingly, this heat transfer process winter outwardly maximal.

Negative effects start in winter when the outside air temperature drops below the "dew point" - the temperature at which vapor condensation begins. Moisture condenses on the film runs down and gets on a heater.

If water gets into the insulation leads to wetting it (especially if it is mineral wool) and loss of thermal efficiency - house gives heat faster.

However moistened and rotting wooden truss system design, because of which the roof loses bearing capacity and may break.

Remember, in the beginning of the article promised you a link to the previous material? Here she is.