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Are glass textiles with PTFE coating used as vapor barriers for installation under the roof?

Home Improvement Asked by gotwo on March 2, 2021

In construction in Central Europe are in use vapour barriers, in special cases more precise as vapour retarders. These enable the drying of building materials such as insulation, if moisture has coming in. On the other hand, these prevent as second barrier the penetration of water from the outside, such as dripping water by rain. The effect is analogeous to some outdoor clothing. A common installation in Central Europe is, from outside to inside: roof tiles – laths – air layer (2…4 cm) – vapor retarder – insulation.

Nowadays, predominantly is used for that polyethylene or polypropylene textile with a plastic coating. The problem is that the resistance of that plastics decreases with increasing temperature. The vapor barriers may decompose on the time.

There are materials available with a significantly higher stability such as glass fibers and PTFE. These materials are already used in building construction. But, to my knowledge, not as a vapor barrier.

My question is therefore: Are glass textiles with a slightly open-pore PTFE coating also used as vapor retarders in buildings?

If not, why not? Or what are other suitable alternatives?

One Answer

One reason could be the important general insulation/anti-mold rule for moderate climate zones like Central Europe:

A vapor barrier should be close to the warmer inside layers. The insulation layer should be close to the cold outdoor side. And the inner window glass should be the coldest surface in a room, enabling condensation on a well defined suited surface.

That way the dew point most likely is not inside the wall or on the wall paper/plaster which has organic material to feed fungi.

To get precise information, this web site may help:

Ubakus.de

It contains many construction/insulation material, foil layers can be inserted everywhere to see the difference.

Possible problems will be shown in a second.

Experimenting/researching is easy by switching on/off of layers.

R-value can be shown by clicking on the spanner/tool icon next to the U-value.

It is free for private use.

Fastest way is to choose an adequate example (menu) and to edit the layers.

Answered by xeeka on March 2, 2021

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