The main enemy of any roof is moisture, which damages the rafter system and reduces the effectiveness of the thermal insulation layer.
To protect the roof from moisture, waterproofing and vapor barrier of the roof are used. The vapor barrier device and the materials used for this will be discussed in this article.
Vapor-permeable waterproofing under-roofing films are designed to prevent excessive moisture of the roof structure, protecting it from atmospheric influences in the form of precipitation, without interfering with its ventilation..
It is most often used when roof vapor barrier is performed - material in the form of films sold in a wide range in rolls and outwardly similar to each other.Despite the apparent similarity, different types of vapor barrier films differ significantly from each other in different vapor permeability.
Highly vapor permeable vapor barrier
Highly permeable vapor barrier for roofing includes materials whose vapor permeability is more than 700 g/m3 per day, reaching in certain cases 3000 g/m3 per day. The Sd indicator, inversely proportional to vapor permeability, is not more than 30 cm.
Such vapor barrier materials are also referred to as superdiffusion membranes or diffusion films. Water vapor easily passes through them, which prevents their condensation, which causes moisture in the layer of mineral wool, designed to keep heat in the under-roof space.
This allows contact between the membrane and the insulation without creating a ventilation gap in the gap between the materials. Outwardly, such a roof vapor barrier device looks like fabric or paper.
Important: when choosing which vapor barrier to equip for the roof, it is important to consider that it can consist of two or three layers.
In both cases, the main component is a vapor- and waterproof polyethylene or polypropylene film laminated with a special polypropylene protective fiber.
In addition, there are four-layer membranes reinforced with a reinforcing mesh made of polyethylene or polypropylene fibers.
The films from which the roofing vapor barrier is made can be painted in the following colors:
- Black;
- White;
- Yellow;
- Blue;
- Grey;
- Bright green.
Unlike high-vapor-permeable membranes, low-vapor-permeable films, due to their structure and the raw materials from which they are made, let through a much smaller amount of water vapor. The vapor permeability of such films is only 25-40 g/m3 per day.
Vapor barrier materials
Before vapor barrier films were developed, roofing material was most often used as a material for vapor barrier, which is still quite common today. More details on how the roofing vapor barrier of the roof is performed - videos and other materials can be found on the Internet.
The roofing material is fastened to a rigid flooring made of boards connected to a groove-comb or from OSB boards nailed to the rafters. Leave a gap under the deck for ventilation.
This is a fairly effective way of vapor barrier, but rather expensive given the rise in price of wood. Therefore, it is more profitable from a financial point of view to arrange a vapor barrier from a film that does not need to be laid. In this way, for example, the vapor barrier of a flat roof can be made.
For roofing of the house having complex structures or a large number of elements such as lucarnes, skylights, kinks, etc., air circulation through ventilation gaps may not always be unhindered. Therefore, the use of low-vapor-permeable films is more appropriate in the case of roofs of a simple shape, for example, a gable roof.
It should also be borne in mind that under the influence of sunlight, the vapor barrier film may lose its water resistance and become brittle, which will lead to its rupture.The most dangerous in this regard is the period when the film has already been laid on the roof, and the installation of the coating has not yet been completed and the film is exposed to ultraviolet rays.
Therefore, roof waterproofing and vapor barrier are usually carried out immediately before proceeding with the installation of the roofing.
Important: scattered sunlight can also penetrate under the laid coating, which leads to a decrease in the effectiveness of the vapor barrier under the roof.
Special vapor barrier
In addition to the usual low and high vapor permeability films, there are also films made for use with specific roofing materials or structures:
- Films for metal tiles, characterized by increased resistance to high temperatures. This is due to the fact that the metal coating heats up quite strongly under the influence of sunlight.
Therefore, special films are produced that provide additional protection against ultraviolet radiation and prevent a decrease in the effectiveness and durability of the film. roof waterproofing.
Important: if the attic room has not yet been insulated and finished, the slopes should be closed to prevent sunlight from hitting the vapor barrier material.
- Another variety of specialty vapor barrier films on the market are aluminum-coated films designed to reflect excess heat..
This avoids overheating of the interior, located in the attic, in the summer. - Films intended for laying on hard flooring are similar in their functions to roofing material, which is laid on the same base..
Films differ from roofing material in their smaller thickness and high vapor permeability, therefore, in the case of OSB flooring and its coating with such a film, a ventilation gap should be left under the base.
When laying the film over a deck made of butt-joined boards, no gap is required. - Films equipped with an adhesive tape that allows sealing the joints of adjacent film strips. Such films are recommended for use in cases where absolute tightness of the roof is required, for example, when the angles of inclination of the slopes are less than those recommended by the roofing manufacturer.
In addition, this type of film can be used in houses located in the mountains, near the sea or on slopes - in conditions where there is a risk of blowing snow or rain particles under the roof with strong gusts of wind.
Installing a vapor barrier film
Most vapor barrier films are quite easy to attach to any surface:
- To fasten them to wooden structures, galvanized nails with wide hats or staples driven in with a construction stapler are used;
- Fastening to surfaces made of metal, brick or concrete is carried out using construction double-sided tape or tape with an adhesive coating.
Before proceeding with the installation of the film, it is necessary to carefully insulate and seal all places where it will be attached to the relief elements of the roof. Such elements include chimneys, ventilation ducts, antenna mounts, etc.
Important: for chimneys and chimneys, an additional layer of insulation should be applied, as the heat emanating from them can damage the vapor barrier film.
Heat from the interior rises, so the film with the applied foil layer is positioned so that this layer is directed inside the house, reflecting heat and preventing it from dissipating in the atmospheric air. A gap should be left between the film and the heat-insulating material, which provides additional heat retention.
Hydro and vapor barriers are an indispensable element of the roofing pie, which makes it possible to avoid a decrease in the effectiveness of the heat-insulating layer as a result of the accumulation of excess moisture and water vapor in the under-roof space. There are several types of materials for vapor barrier, the choice of which should be made in accordance with the climatic conditions of the area where the house is built and the design of a particular roof.
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