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Install the vapor barrier correctly - how it works!
In some cases, a vapor barrier must still be installed on extensions. Here, special care is required: A vapor barrier can only achieve the promised tightness (Sd value) if it is installed correctly.
When is a vapor barrier required?
According to today's findings of building physics, a vapor barrier is only required in exceptional cases: These are cases in which a high static moisture load is on a component. A static moisture load is given when moisture only ever wants to penetrate from one direction into a component, then it moves from warm to cold. Like in a cold store: The moist and warm outside air would like to get into the interior here. The other way around with a steam bath or a sauna. In both cases, a vapor barrier is necessary. It is always applied on the warm side.
In most other cases today the attachment of a vapor barrier recommended. This is not only because a vapor barrier usually either leaks when it is being cultivated or later because the material is fatigued. It has also been found that in most components a moisture exchange is normal and contributes to a healthy indoor climate.
Even in typical problem cases such as non-permeable exterior facades or roofs, experts today no longer recommend a vapor barrier. If a roof is tightly covered (bitumen, slate, sheet metal) or if plastic (synthetic resin dispersion) or sheet metal
close the facade, was formerly always on the inside of a vapor barrier raised. Likewise, the Council was dense outer walls (heavy natural stone, waterproof concrete, glazed or sintered clinker).
However, experience has shown that a vapor barrier lets moisture through too often, which then can not get away and causes damage. Therefore, films have been developed with variable vapor permeability, the escape of moisture can escape again. They should help in these problem cases, to maintain the building fabric longer.
A vapor barrier must be tight
If a vapor barrier is recommended according to current knowledge, its purpose is to exclude moisture. She can only do that if she is really tight all around. Exactly this condition is not easy to ensure. That's one of the reasons why vapor barriers are barely used today
become. Any minor assembly error can cause moisture to pass through the vapor barrier and then condense in the insulation material, which can be extremely unpleasant.
Install the vapor barrier correctly
- First, you need the right materials for the attachment. This means a suitable adhesive tape and the right elastic film adhesive, since even at these details the tightness of the vapor barrier could fail. To prevent this from happening, the vapor barrier must first be in the right place in the wall structure. It is placed on the inside of the insulation material, only then comes the wall covering.
- The vapor barrier must be absolutely airtight. To achieve this goal, the films are overlapped and then glued airtight with the right tape.
- Particularly critical is the tight bonding in the range of sockets and other wall outlets. Here you can be successful if you use an elastic film adhesive.
- Under no circumstances should the vapor barrier be damaged after installation. Any hole in the wall, whether hanging a lamp or stabilizing a shelf, increases the risk of perforating the vapor barrier.
- Even through small openings moisture can already reach the insulation material. The consequential damage would not be long in coming.
Counter battens - yes or no?
It is often recommended to secure the vapor barrier after attaching it with a counter battens. The inner panel can then be mounted on the slats. This also creates space for circulating air, which should ensure that it is on the inside
no moisture settles. But that is not undisputed, since every attachment yes, the vapor barrier injured again. Although there are technicians of the dealer companies who believe that staple needles are a negligible size, but there is a violation. Others therefore advise an additional adhesive layer over the fixtures.
Tip from the editor
- Since the vapor barrier density is so important, you should consider investing in a blower door test. This test measures whether the construct is truly airtight. Because the correctly installed vapor barrier not only keeps the moisture in check, but also plays a decisive role in the insulating effect of the wall construction.