If the attic insulation requires a vapor barrier

Attach the vapor barrier or vapor barrier correctly

The vapor barrier or vapor barrier is intended to protect buildings from the ingress of moisture. For optimal functionality, you must attach the two building materials very carefully and properly.

Vapor retarders or vapor barriers consist of a film that is impermeable to water vapor and serve as a protective cover for the wall or roof insulation. An incorrectly installed vapor barrier or vapor barrier, however, is often the reason for extensive moisture damage. You should therefore be very careful when installing it so that the aluminum or polyethylene film can ensure that no moisture can penetrate the building's insulation material.

The two terms vapor barrier and vapor barrier are often used synonymously. However, this is not entirely true. Although the two building materials have similar tasks, they are different in their effect and structure.

Difference between vapor barrier and vapor barrier

The main difference between the vapor barrier and vapor barrier is the diffusion resistance. This value indicates the level of resistance of a building material to the spread of water vapor and is measured in building physics as a so-called SD value according to the DIN 4108 standard. With a vapor barrier, this SD value is significantly lower.

Vapor barriers have an SD value of at least 1,500 meters and are therefore considered to be diffusion-tight or impermeable to water. It could therefore be assumed that this method protects a building from moisture better than a vapor barrier. But it is often the case that the vapor barrier film is the reason for serious moisture damage in many cases. Because if a vapor barrier is not 100 percent tight, mold formation, heat loss or a reduction in the insulation function can occur.

However, problematic areas such as connections to windows, pipes or sockets often lead to poor workmanship. Another mistake is that the possibly perfectly attached vapor barrier was installed when it was damp and now prevents the water contained in the components from escaping.

Since these construction defects occur relatively often, many builders do without vapor barriers and instead install vapor barriers. These have an sd value of at least two to a maximum of 1,500 meters.

Reasons for vapor barriers or vapor retarders

Warm and humid air in the home is caused by many different activities. For example when cooking, bathing, showering or simply breathing. Without a vapor barrier or vapor barrier, this moist air now escapes through the wall to the outside. This can lead to the formation of condensation, mold or other moisture damage in the building structure. In order to curb these flows of humid air, you have to attach vapor barrier films or vapor barrier films.

These diffusion-inhibiting or braking foils are particularly important when extending roofs or when erecting wooden or prefabricated houses. In contrast, in solid houses made of walls or concrete, the climate membrane can be dispensed with. If the insulation layer is particularly thick and effective, the formation of condensation on the outer surface of the wall below the insulation layer is not possible.

Attach vapor barrier

To protect your building from moisture damage, you should attach the vapor barrier carefully. Read here how to do this:

1. Select materials and tools

For a successful installation you need special vapor barrier adhesive and vapor barrier adhesive tape. An adhesive connecting tape should always be available to connect the strips. With these materials, you should not save, but pay attention to the recommendations of the manufacturers.

2. Lay the vapor barrier film

Basically, you must always attach the vapor barrier facing the interior. In order to avoid consequential damage, special care must be taken with the film seams and the connecting parts on windows and sockets.

It is best to lay the vapor barrier film directly above the rafters. To do this, staple the film to the rafter at a distance of between ten and twelve centimeters and a depth of at least eight millimeters. You can only stick the vapor barrier film on solid backgrounds, as only these can withstand the pressure required to be pressed on.

3. Keep supernatant

At the wall connection, you should keep a protrusion of at least 15 centimeters so that no moisture can form through the gap.

4. Seal the vapor barrier films against each other

Now that you have stapled the individual strips onto the rafters in an overlapping manner, you have to mask them against each other in a vapor-tight manner. You can now use the vapor barrier tape to do this. You place this on the rafter and glue it over the side edge of the second vapor barrier film, ideally also over the staples. Then the whole thing will be really tight!

5. Breakthroughs and connection points

With the help of the vapor barrier tape or the vapor barrier adhesive, you can fix and seal openings and connection points. An installation level between the vapor barrier film and the inner lining is recommended to avoid the vapor barrier being punctured often. Because every opening for sockets or other components can lead to moisture getting into the insulation.

6. Take precautions with expansion folds

If the vapor barrier is connected to more than one component, changes in temperature can cause the components to expand differently. Just a few millimeters can cause the vapor barrier to tear. The best way to prevent this from happening is with stretch wrinkles. To do this, the vapor barrier film must simply not be pulled too tight so that it is free from tension. It is even better to push the foils together a little so that a small crease can form.

7. Attach counter battens

Counter battens are attached in order to optimally close the vapor barrier. This forms a spacer between the inner wall of the room and the vapor barrier and ensures sufficient air circulation. Finally, the inner wall can now be mounted on the counter battens.

Check the tightness of the vapor barrier or vapor barrier

If you have already installed a vapor barrier or vapor barrier, you can check the tightness of the film against moisture with a so-called blower door test. A measurement technician will clamp a fan in the frame of your front door and seal it with a film. The fan creates a negative pressure and draws the air into the house. The air extracted by the fan is then measured. If the fan has had to vacuum a lot, there will be leaks.

In addition to the blower door test, thermal images are now taken with an infrared camera to find out where the leaky gaps or damage are. Alternatively, you can also use a smoke machine. When the smoke approaches a leak, there is a noticeable increase in air movement.