Vapor barrier for the roof of the house

Any building structure is exposed to atmospheric precipitation, which can destroy the operational characteristics of the building material. Currently, various modern heat-insulating materials are used in the construction of houses.

Steam Insulated Roof


  • Why is it necessary?
  • Materials
  • Polyethylene films, with or without perforation
  • Polypropylene films
  • Breathable films or membranes
  • Mounting technology
  • Recommendations

Moisture penetration is the main enemy of any roof. Vapor barrier and waterproofing, which protect the structure, namely the roof, from moisture, helps to prevent moisture from entering the insulation.

They are designed to protect the roof, namely the roof insulation, from weather vagaries. These are two completely different materials that differ in their properties. They do not need to be confused at all, since the insulation will be damaged and both protective layers, thus, it will be necessary to redo the entire structure of the insulation.

Everyone knows that warm air rises up, accumulating near the ceiling, and cold air goes down. In order for the roof to be able to retain heat for a long time, a heater is used, which is located under the roofing.

However, to get good thermal insulation, one insulation is not enough. Just the insulation is a place for the accumulation of water condensate, which appears due to the steam going up. And on top of the same insulation material, moisture seeps out and concentrates also on the insulation. It turns out that protective coatings above and below are very necessary.

Accordingly, vapor barrier does not allow the penetration of moist air from the room into the insulation. Waterproofing does not allow accumulated moisture to penetrate into the insulation. And also it turns out that waterproofing passes moist warm air that passes through the vapor barrier. A vapor barrier, in turn, does not let out anything at all.

Between these materials there are differences in appearance. On the waterproofing material there are small holes for air passage, which are not on the vapor barrier film.

Why is it necessary?

Steam Insulated RoofVapor barrier - A very significant element in the construction of any building and structure.

If you think carefully and reflect on where the moisture comes from and what the consequences are, it will immediately become clear how important the vapor barrier of the roof is during construction.

Warm air, saturated with vapor and accumulated near the ceiling, tends to go outside. Accordingly, steam penetrates into the insulation and if the insulation is not protected, the insulation will begin to collapse.

The protection of the insulation in winter is especially important. The steam that enters the heater, at low temperature turns into frost, then into ice crust. With the onset of heat, the ice melts and flows, while the insulation will lose all its necessary qualities and properties.

The main task of vapor barrier is to prevent the penetration of wet condensate into the insulation. Thus preventing the appearance of dampness and mold, as well as the release of heat from the room.

Vapor barrier is required in those parts of the building where warm and cold spaces are distinguished. This, of course, the surfaces inside the house, basements and roofs, is also an attic. If the structure is sheathed with natural wood material from the outside, the installation of a vapor barrier is not necessary.


In modern times, the construction market offers a wide selection of vapor barrier material.

The most popular and used are film materials and membranes. Their vapor permeability is achieved by microperforation and using a special chemical composition.

The vapor barrier of the roof is mainly produced by three types of film materials:

Polyethylene films, with or without perforation

Polyethylene film for roofing

To give strength, this type of film is used with additional fabric or mesh.Polyethylene films can be produced with foil sidethat goes inside the room.

Polypropylene films

Polypropylene film for roofing

Much stronger than polyethylene.

Breathable films or membranes

Breathable roofing film

They are one-sided, then they can be laid on the heater only by a certain side. In case there is a double-sided membrane, laying can be done by either side. The membrane material is more in demand, in addition to the ability to pass water vapor, this material is not blown by the wind, respectively, the loss of blown heat is reduced.

It is necessary to choose high-quality material for vapor barrier, given that it will be located at the very base of the roof structure, therefore, it is difficult to access during repair. The range of films is quite large, in different colors. Externally, different types of vapor barrier films are similar, but they differ among themselves primarily in different vapor permeability.

Among the many materials for vapor barrier, you should choose based on the climate conditions of the area where the house will be built, and also take into account the design of a particular roof.

The vapor barrier material must be moisture resistant, meet all fire safety requirements, as well as environmentally friendly, i.e. It must not release harmful substances during operation.

Mounting technology

An important condition is the tightness of the film, it must be laid in a continuous layer, avoiding tears and crevices.

Laying the vapor barrier of the roof can begin after installing the thermal insulation, in any direction - horizontally or vertically. The film is attached to the inside of the insulation. It is important that there is a gap between the vapor barrier layer and the insulation, it will provide additional heat storage.

If the material used is a membrane, then it is attached directly to any insulation from its inside. Accordingly, the ventilation gap is not required. This allows you to use the material in the maximum quantity.

When installing vapor barrier material, you must adhere to several mandatory rules:

  1. First of all, Do not lay the film on the old roof. This will provoke the destruction of the roof.
  2. Secondly, the material must be cleaned and dried.
  3. Thirdly, tightness of vapor barrier material is very important. Any slightest leakage is unacceptable.


  1. Laying the vapor barrier material yourself is quite simple. It is easy to install, available in rolls, easy to cut. For fastening to wooden structures, you will need galvanized nails or staples that are driven construction stapler, to a metal surface - double-sided or adhesive construction tape tape.
  2. After the room is prepared, it is necessary to build a crate. You can use wooden planks or a metal crate.
  3. Then immediately begins the installation of vapor barrier. Roll sheets are attached to each other with a slight overlap.
  4. In order for the seams to not leak moisture, they must be carefully glued, they must be hermetically connected. For this, adhesive tape is used.
  5. Next, continue the interior decoration of the roof, covering the vapor barrier material.
  6. Quick and high-quality vapor barrier will help you experts who know all the intricacies of installation and material features.


Steam Insulated Roof

The cost of vapor barrier roofing depends on the manufacturer of the material to be used. Saving on material is better not worth it. Having bought high-quality material, but serve you much longer.

By qualitatively and correctly performing vapor barrier of the roof with high-quality materials, you will protect the thermal insulation of the entire house. A vapor barrier will protect your home from moisture and provide a long roofing service, then the house will be warm and dry at any time of the year.

Quick Tips:

  1. Before laying the vapor barrier layer, thoroughly examine the entire roof and the insulation layer. In case of defects, do not leave them for later, repair immediately.
  2. When vapor barrier window openings do not forget to leave a supply of film on the draft, about 20-30 cm.
  3. The interior ceiling must not come into contact with vapor barrier film. To do this, it is better to attach bars that will fix the insulation layer and form the air space between the casing and vapor barrier.

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