Mineral wool is a very effective insulation material; it perfectly keeps heat in winter, reducing heating costs, as well as keeps coolness inside the building in summer. This material is made of the finest fibers, which are 2-60 mm in length. Due to air pores between the fibers, the amount of which is up to 95%, mineral wool possesses its insulation properties. The process of laying mineral wool is simple, it does not take much time and any ordinary citizen can perform it.
This kind of material is a good choice for thermal and sound insulation. Price-quality correlation is entirely commensurable in this case, so this building material is in demand both in private and industrial construction.
While using mineral wool, for example, in order to insulate the attic, you should thoroughly follow safety instructions not to cause irritation of respiratory tract or mucous membranes of the eyes. Before starting the work, it is also a good idea to get high rubber gloves and a good knife.
It is important to decide beforehand what exactly you are going to insulate on the roof. Usually, if you want to keep heat in the rooms of the upper floor, you should insulate the ceilings. In this case, the very roof and its system remain such as they are. That means that the temperature in the attic is almost the same as outside. The big advantage of this attic is that it is well ventilated, and moisture does not stagnate there.
The attic ceiling is usually insulated either from above (covering), or from below (underlining). However, the problem arises when the owners decide to do the living room in the attic. Then you cannot do without additional insulation of the roofing “pie”.
As it turns out, a lot of icicles appear on the eaves of the house because of the lack of roof insulation. The snow that is lying on the roof is heated from below. When this heat passes through a thin layer of insulation, the snow thaws and the water runs from the roof to the eaves. There is no such heat there, the snow freezes again, and turns into icicles.
Properly installed modern roof insulation will save more than 3 kW of electric power (for a building with an area of about 205 m²), and this can significantly reduce heating costs.
The peculiarities of air and humidity in the house
Warm air is always more humid inside the building than outside. Therefore, besides the difference in temperatures, water vapors play an important role. They also try to “fly out” through the roof covering. But, in this case, vapor diffusion has a resistance in the form of the roof. The thing is that the main purpose of roofing is waterproofing, and roofing materials are arranged in such a way that no moisture passes through either from above (from the sky), or from below (into the sky). Therefore, water vapors may turn into condensate inside the building and permanent wet stains and mold may appear there soon.
The roof is normal, there are no leaks, but it is still humid inside the building and insulation material gets wet. The reason for this is the condensate. To fight it, it is worth to do the following: the insulation material should be protected from moistening by using a vapor barrier layer, which is put under the insulation layer. If the moisture somehow penetrated the vapor barrier and passed to the roof, waterproof tape should be put between the insulation material and roofing, and ventilated air space should be left there.
Wind is one more “enemy” of heat and thermal insulation on the roof. If the roof rafter system is not powerful enough and the insulation material is not thick, but rather thin (low density), the wind blows through it and “steals” the heat. To provide the protection from the wind, the insulation material should be covered with wind and vapor resistant material.
Waterproofing is the last “defensive line”. Its main function is to protect the insulation material and roof construction from getting wet (due to slanting rain, snow thawing, etc.). When the roof construction is moistened, its durability becomes lower; appearance becomes not so attractive, and when insulation material gets wet, its insulation properties become worse. Therefore, it is necessary to realize the importance of proper installation. Waterproofing material should be fastened reliably (with straps or rustproof nails to joists). It is mandatory to follow rules of horizontal and vertical overlapping. Joining of the boards should be performed in such a way that their parts overlap (in 100 mm width), vertical and inclined surfaces should be covered bottom up with an overlap onto the horizontal surface (25cm).
The width of the gap between the insulation material and the roof also depends on the specific material, in this case, on the roofing. If the roof is covered with corrugated sheets of galvanized steel, tiles, metal tiles or other corrugated sheets, the ventilated gap in the roof should be at least
25 mm. If flat sheets, such as asbestos-cement, soft shingles, galvanized steel, rolled materials, are used, the air gap should be 50 mm.
Insulation material installation
Hard or soft mat insulation is put into the cells of roof lathing, i.e. between the rafters (usually the spacing between them is 60-100 cm). Basalt wool boards are usually used for the roof insulation. They may be laid in one, but preferably in several layers. When installing insulation material in several layers, joints of the boards should be staggered.
The thickness of various insulation materials may be different. The main point is to remember that
the lower the thermal conductivity of material is, the better it keeps the heat, and the thinner layer it can form. The coefficient of thermal conductivity of the material is always indicated on the wrapper and is marked by letter «n». If n = 0,037 W/m °C, it will be enough to use the insulation material that has a thickness of 160 mm; if n = 0, 05 W/m °C and higher, you need a thicker insulation material (225 mm).
Possible mistakes which may occur in the process of insulation material installation
The mat should fill all the space of the cell, without hollows and cavities for air passage. If insulation material is narrower than the width between the rafters, “cold bridges” will remain. If it is
wider, it will bend toward the ventilation gap and can get wet because of condensation. It should be controlled. Pieces and scraps that are left are used to insulate the ridge, door and window frames, chimneys and so on.
Installation must be done bottom up. Insulation boards should be tightly clamped one to another. This installation procedure will help avoid gaps between the boards, which lead to freezing, and consequently, the ice formation on the surface of the roof.