vapor barrier

Concept of vapor barrier

The term vapor barrier is understood in structural engineering to mean a cardboard or foil which is intended to prevent or substantially prevent the formation of condensation within components from the field of thermal insulation. Steam brakes thus have the task of limiting the formation of water vapor and a flow of indoor air to a minimum. It should not be completely prevented by water brakes of the resulting water vapor, as is the case with the so-called vapor barrier. Steam brakes thus have the advantage that any penetrated water of the resulting water vapor can evaporate again. This process is not possible with a vapor barrier.

The legal background

In accordance with the provisions of the Energy Saving Ordinance (EnEV), steam brakes are mandatory in Germany. This regulation is reflected in German commercial law and is mainly aimed at the roofs of office buildings, residential buildings and factory buildings, which have normal indoor temperatures. Legislation assumes an average interior temperature of 19 degrees Celsius and a heating period of more than four months. This includes all buildings that are primarily intended for living.

The second category is those objects that average 12 to 19 degrees Celsius and are also heated for more than four months. Here, however, all room air and heating conditions of the building are to be included. Basically, the contents of the EnEV impose standardized requirements on all responsible installers of these buildings, which are intended to restrict general energy consumption through structural measures. In addition, this regulation contains specific regulations on the extent to which vapor barriers must be used in new buildings or in existing building stock. Excluded from the EnEV, and thus also the use of vapor barriers, are buildings that fall under the protection of historic monuments and meet the requirements prescribed by the respective state authority. Furthermore, among other things, in the case of buildings for animal husbandry, in underground buildings, in greenhouses, in constantly erected and disassembled halls and tents and in permanently open operating objects no vapor barriers are required by law.

The materials of a vapor barrier

In the case of vapor brakes, a distinction is generally made between normal or simple and so-called "intelligent" vapor brakes. The second difference lies in the so-called sd value, which expresses the diffusion-equivalent thickness of the air layer. By way of illustration, a vapor barrier having the sd value of 1 has the same water-diffusion resistance for a H 2 O-water vapor molecule as a one-meter air layer. More simply, a vapor barrier with a high sd value is far more dense than a vapor barrier that has a low sd value. By design, most simple vapor barriers are products that look like a thick foil and are made of plastic.

An intelligent vapor barrier, on the other hand, consists of polyamide, which also finds useful application in films for the food industry. Because of the positive properties of the polyamide, vapor brakes made from this base have the ability to conform to and absorb the prevailing weather conditions, especially the permeability of water vapor. This is based on the chemical process that the higher the ambient humidity, the more H²O water vapor molecules are absorbed by vapor barrier made of polyamide.

The advantages and disadvantages of a vapor barrier

In addition to its basic functions as thermal insulation and the prevention of excessive humidity, a roof brake has a major advantage, especially in terms of installation. Its weight makes it light and easy to lay with a simple rolling method. In addition, steam brakes have a high elasticity and good adhesion to absorbent substrates. These films also improve the climate in the room because they provide the necessary exchange of humidity.This also means that an existing high humidity is avoided by a vapor barrier and subsequently no sauna effect occurs in the attic. In addition, they also provide for an often necessary moderate air density, which is not given by a vapor barrier. The overwhelming advantages of vapor brakes are actually only a few disadvantages. Since vapor barriers are laid indoors, there may be some restrictions on the living space. The biggest disadvantage, however, arises when a vapor barrier with a wrong sd value is selected. As a result, problems with the indoor climate are inevitable, which are difficult to repair again. Basically, the right sd value depends on the consistency and diffusion behavior of the outer components. In addition, it can lead to an improperly carried laying or even the slightest damage to the film that the effect of the vapor barrier is significantly limited both on the flat roof, and on the pitched roof.

The laying of a vapor barrier

As a rule, vapor barriers are laid inside, ie on the heated side of a loft. At the beginning of the installation, the webs of the film must be overlapped on the rafters of the roof construction. The overlap should be at least five to ten centimeters.

This is best suited a stapler, with every ten centimeters should be placed a point of attachment. Then the overlap area of ​​the individual foils should be taped waterproof with an adhesive tape.

Where vapor barriers are available

Basically vapor brakes are available from different manufacturers in every well stocked hardware store. A well-known manufacturer of vapor brakes is, among others, the company Bauder, which distributes vapor brakes in various designs and sd values ​​in the building materials market throughout Europe and worldwide. In addition, there are numerous suppliers of vapor barriers on the Internet who offer their products online for sale.