All about vapour control film in brief

A vapor retarder is a film used in the construction process to seal an insulated structure from the warm side (inside). The film provides an airtight seal so that warm air cannot escape, which directly prevents energy loss. In addition, the foil also ensures that vapor pressure is held back. Hence the name vapor retarder film.
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What does a vapor retarder film do?

In an insulated space, it is usually warmer inside than outside. In addition, the air inside usually has high humidity. That is, there is vapor in the air.

With the naked eye, this can only be seen at extreme humidity levels such as after showering in the bathroom. You see that the mirror fogs up or vapor condenses on the windows. When there is a higher humidity and temperature inside than outside then vapor pressure is created.

A vapor retarder film provides resistance so that the vapor stays inside the warm air and no energy is lost. In addition, a vapor retarder film ensures that vapor cannot penetrate the film in undesirable quantities, thus preventing mold and wood rot.

When do you use a vapor retarder?

A vapour control film can be used in roof and facade constructions and is always applied on the inside of the construction so on the warm side of the insulation.

Al onze dampremmende folies op een rijtje

Where is vapor retarder film used?

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Technical drawing Miofol VS2
Technical drawing TAFTEX IN-100

Why is a vapor retarder important?

Prevent condensation with a vapour control film

Because warm air can hold more moisture than cold air, condensation occurs when warm air cools to the outside. In an insulated house there is a high humidity of the warm air which can cause condensation in the structure if it is not properly sealed by the proper foil. This condensation can then cause mold, pests or wood rot. In addition, the performance of the insulation material is significantly reduced when it is damp.

Preserving a structure

Insulating and preserving a structure is hugely important for improving the energy performance of a building or home. It directly contributes to a lower energy bill but above all ensures a reduction in harmful emissions. Insulating a roof or wall can be a substantial investment with installation and finishing.

A fraction of this total cost is the cost of a good vapor retarder. Therefore, do not skimp on the film and choose a film with proven performance.

Increase your insulation value

When you decide to insulate a room you can choose different insulation materials. Insulation is nothing more than a layer that reduces the temperature differences between a cold environment (outside) and a warm environment (inside). This usually happens because of low thermal resistance. A low thermal resistance, meaning a high insulation value, means that warm air cannot easily be cooled by the cold environment outside.

However, most insulation materials, such as glass or rock wool, do not counteract air currents that allow warm air to escape. This also happens when insulation boards are not connected airtight. A vapor retarder prevents warm air from escaping from inside. In other words, if no vapor barrier foil or the wrong foil is applied then warm moist air will escape through the insulation to the outside and this has a negative effect on energy consumption.

When do I not need a vapor retarder?

In certain constructions it is recommended to use a vapor retardant membrane instead of a vapor retardant membrane. When the amount of humidity is so high in a bathroom, for example, we speak of climate class 4. In these cases, a vapor retarder will still allow too much vapor to pass through and a higher vapor resistance is necessary. Therefore, in the case of climate class 4, we recommend the use of a vapor-tight film, such as the Miofol® 125 AV or Miofol® 150A.

There are also constructions where the cold side of the insulation is completely sealed. Consider a flat roof with bitumen roofing or EPDM. In these constructions, the cold side is already vapor-tight and an intelligent vapor retarder or climate film such as the Miofol® Active or Tyvek AirGuard Smart should be used on the warm side.

What is an Sd value?

An Sd value or also µd value is the degree of vapor diffusion resistance. Or the degree to which a material provides resistance to vapor pressure. The higher the Sd value of a given product the more vapor is retained. The Sd value is expressed in meters because the value indicates what the vapor diffusion resistance of a given material is expressed in meters of air.

For example, a vapor-permeable product such as Tyvek or Polyex® has an Sd value of 0.02 to 0.04 meters. A vapor retarder can vary between 3 and 100 feet. In fact, the Sd value of vapor-tight films is much higher than that.

How should you apply a vapor retarder?

With staples

  1. Roll out the foil with the print legible
  2. Do not attach the foil to the structure. Limit the number of staples or apply them where the overlap of the next job will be later to avoid perforation.
  3. Tape off visible staples and overlaps with the appropriate airtight tape such as VAST-R® Foil Tape Basic.

With double-sided tape

  1. For an airtight attachment without staples, use VAST-R® double-sided tape, VAST-R® Sealpro or VAST-R® Butyl tape.
  2. Apply the double-sided tape to the substructure and press firmly.
  3. Remove the release layer
  4. Roll out the film with the print legible and press against the double-sided tape.
  5. Rub after for proper adhesion.

Why are Miofol® vapor retardant films the right choice?

We are proud to say that Miofol® vapor retarder films are the most widely used by professional processors. Miofol® is the result of decades of further development and is therefore present as a product group in a large part of the existing building sector. Miofol® is, in contrast to many PE films, CE marked which is a requirement for application in the construction industry today. The composition of Miofol® has been carefully developed so that the properties of the film are guaranteed over the long term.

A vapor retarder film is exposed to temperature fluctuations during its lifetime. When a film heats up and cools down for years, it can lead to a limitation of flexibility and function in the long run. With Miofol® you buy security made in Holland.

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