Roof insulation

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Roof insulation

It is known that the roofing cake consists of several layers (that is why it is called). It can include a different number of inter layers, but
Hydro, heat and vapor barrier remain unchanged. And if the waterproofing is designed not to allow moisture to penetrate the inside of the house, the vapor barrier does not allow the evaporation from inside to get into the roofing cake.
It is extremely important to place the vapor barrier below the thermal insulation material. However, we all know that there are also insulated roofs, can not they be made without a vapor barrier Unfortunately, no — the vapor barrier not only preserves the insulation, but also maintains a comfortable indoor micro climate. If it does not exist, the house will be very stuffy and damp, and comfortable housing will turn into an ordinary greenhouse.

To fully appreciate and understand the structure of the roof insulation, it is necessary to study the structure of the roofing pie:
Roofing can be continuous or consist of segments (tile, slate). It is placed on a wooden crate or a solid foundation.
Waterproofing layer — protects the next layers from penetration of moisture from the outside. It is a waterproof non woven material that is attached to the crate, leaving a small gap between the next layer.
Insulation — roofing thermal insulation materials are plates with minimal thermal conductivity. They can be made of pressed mineral or stone wool, polystyrene foam or polyurethane foam. Depending on the material differs and water absorption, which also affects the choice of vapor barrier. Polyurethane foam and polystyrene are practically not afraid of moisture, but mineral and stone wool require the installation of high-quality vapor barrier.
The vapor barrier layer — films or membranes are installed on the lath immediately after the heater and leave a gap between the casing ceiling material to ensure natural ventilation. When the water vapor from the bottom comes to the membrane, condensation forms, which will drain down and dry out due to the ventilation of the under-roof part.
Even the most high-quality and modern vapor barrier will not “work” if you do not take care of ventilating the roof. Ventilation is important at any time of the year — in the winter it will help to keep heat and prevent icing of the roof, and in the summer will give more coolness.
If there is no vapor barrier in the roof of the house or it is not properly installed, this inevitably entails the formation of non-eroded condensate, dampness, mold and fungi. Eventually, wooden structures and roof elements will rot and decay.

Steam insulation materials

Today in the construction market you can find a lot of roofing materials. In the majority it is a film based on polyethylene. They are waterproofing, vapor barrier and antioxidant. The latter are special in that they are covered on the inside with an absorbent, fleecy fabric layer, which actively collects the condensate, preventing it from reaching the next layer of the roofing cake.
Previously, the main material for the vapor barrier of the roof was parchment. Today it is used only by economists who are too economical, but if we look at the performance of the glassing and compare them with the qualities of modern materials, then the profitability of the latter will be obvious.
Depending on the physical and technical parameters, it is possible to distinguish three types of vapor barrier films:
Polyethylene — are used not only for steam, but also for waterproofing. There are perforated and non-perforated films. In any case, when mounting it is recommended to reinforce with a light mesh or cloth. Perforated films mainly serve to provide waterproofing, perforated — vapor barrier. It would seem strange, because the “leaky” surface lets in water, but the holes in the film are so small that the water just does not have time to leak through them. They serve for better ventilation of the roof cake. Also, there are foil-coated polyethylene films, one side of which is able to reflect the heat coming from below (from the house). Therefore, laying such a material follows the mirror side down.
Polyethylene vapor barrier is supplied in rolls. During the installation, the material cuts are glued together with special seals and connecting adhesive tapes. Thus, a dense monolithic layer is obtained.
Polypropylene — are more durable than polyethylene films. Used mainly for laying the waterproofing layer, but can also serve as a vapor barrier. On the one hand, they have antioxidant coating from viscose-cellulose tissue.
Diffuse — a material that appeared only a few years ago. It is a well-ventilated membrane that has an increased vapor permeability, but does not allow moisture to pass through. The main advantage of such a “breathable” vapor barrier is that it does not need to adjust the ventilation gap in the under-roof space. Thus, you save space and time.
A diffuse vapor barrier film works very simply — when steam passes through it, it settles on a rough layer, absorbs into it and evenly dries, leaving the insulation dry and unharmed. There are single and double-sided films. One-sided can be stacked only in a certain way on the heater, two-sided — as you please.

All film materials used for vapor barrier insulation must have good elasticity, be resistant to tearing and as convenient as possible. It is extremely important that the vapor barrier film does not tear during fixing, but wraps around the fastening element. Even with accidental mechanical damage to the roof, for example, because of the tree branches fallen during the hurricane, the vapor barrier must remain intact, minimizing losses. Ideally, the thickness of the vapor barrier of the roof should be such that the material can withstand the load of heat and waterproofing, if the crate and rafters can not stand.
Isospan vapor barrier
One of the most popular materials on the domestic market is the vapor barrier of the roof is isospan. It is relatively inexpensive, has excellent operational characteristics, durability and ease of installation. The isospan can be used for waterproofing and as a barrier for steam at the same time.
The manufacturer offers several modifications of Isospan, each of which is designed for a specific purpose, but there are also universal films. Therefore, it is very important to clarify the characteristics of the selected material before purchasing, so as not to accidentally buy the wrong variation of Isospan.
Izospan B is widely used among professional builders and self-taught masters. It can be combined with any type of roof covering. In addition to protecting the insulation from moisture, it prevents microfibers from pouring into the premises, as is often the case with other materials.

Installation of vapor barrier

It does not matter if you make a vapor barrier for a flat roof or work with a gable roof — the film or membrane should be installed only after the insulation has been laid.
Features of installation of vapor barrier:
Cloth can be installed both vertically and horizontally.
If you prefer horizontal mounting, start the installation from the top.
Lay cuts of canvases with an overlap of at least 10 cm. Be sure to paste the seams with one-sided or two-sided adhesive tape.
Choose a wide tape at least 10 cm.
Double-sided tape is glued inside the overlap — first glue it on the bottom layer, then remove the protective coating and fix the top with overlap.
If you are laying a vapor barrier along the rafters without a draft of the insulation, do overlapping and fixing the canvas directly on the rafters.
К деревянной обрешетке или стропилам пароизоляцию крепят строительным степлером или оцинкованными гвоздями (не ржавеют).
It is recommended to strengthen sizing plates with clamping plates. This advice is especially relevant for roofs with a slope of up to 30 degrees and with loose thermal insulation.
At the points of contiguity to the aisles, manholes or roof windows, a so-called mansard apron must be organized through the roof, which is usually included in their configuration. If it does not, glue a 2-sided betel tape around the perimeter of the window frame or the opening.
In the places of passage through the roof of water pipes, wrap the vapor barrier material down, wrap it in a pipe and seal it with tape.

When the vapor barrier is laid, attach the bars treated with antiseptics at a distance of 50 cm from each other. Thus, you will create an air corridor, where condensate will quickly evaporate, and the film will not touch the ceiling sheathing. If you use a vapor barrier membrane, you do not need to put bars. But they will be useful to occupy this space with various communications. If you plan to finish the interior of the house with plasterboard, instead of wooden bars use a metal zinc-plated profile.
Errors in mounting the vapor barrier
Very often when building a roofing cake, builders make mistakes that lead to fatal consequences. If you confuse the location of the insulation layers, the roof can become unusable after a year of operation.

We have prepared a list of the most common mistakes in installing a vapor barrier:
Places of abutting the film are not sealed tightly, as a result of which the effectiveness of the vapor barrier is minimized, the insulation is dampened, the rafter structures begin to decay.
Using a narrow adhesive tape to seal the seams — during the operation of adhesive tape with a width of 5 cm or less, it will simply be peeled off. The recommended width of the tape is 10 cm or more.
There is no deformation reserve when working with window apertures — any house shrinks, so you need to leave a stock in the form of a crease of 20-30 mm.
The film around the dormer windows is not protected from the inside — if not done, after a few months of operation, the vapor barrier completely falls into disrepair and collapses under the influence of sunlight.
The film envelops the rafters — if the vapor barrier material goes around the rafter feet, the moisture will penetrate to the wooden elements, as a result of which they will begin to rot.
Where the vapor barrier is adjacent to the inner walls of the house, the mines or the chimney, it is necessary to take into account the specificity of the irregularities to which the material will be attached to ensure tightness of fixation.
If you fix the film to a rough brick wall or a surface of non-planed wood, you can do this only with polyurethane, acrylic glue or synthetic rubber.
Do not use polyurethane adhesive tapes and betel rubber rubbers because they do not stick well and can soon peel off from the surface.
The penetrating power of water vapor is extremely high, so it should be extremely responsible to approach the device of vapor barrier. In addition to the popular Isospan, the Tehnonikol roofing is widely used today. The most important thing is to select the materials correctly and install them in the right sequence, then the roofing pie will last for many years without repair.
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