- How is the thermal protection of a frame house
- Frame system requirements
- Laying insulation into walls
- Insulation protection
- Insulation of floors and roofs
One of the main and serious mistakes in frame construction is associated with the installation of insulation. Thermal protection of a frame house is not just filling the internal cavities with mineral wool. Today Our site of advice will tell you how for proper insulation it is necessary to observe the specifics of the frame device and ensure the protection of the wall filler.
How is the thermal protection of a frame house
To understand what a frame house is, it is enough to familiarize yourself with the set of rules SP 31-105-2002. Although this standard is advisory in nature and, by and large, is ignored by private construction companies, it well reflects the main trends in frame construction. This document is the first attempt to adapt the western frame construction technology to the conditions of the CIS construction industry and the range of materials presented on the domestic market..
When organizing the thermal protection of a frame house, a standard scheme is used, which is based on the elimination of convection at two levels. The mineral filler of the walls prevents the movement of air inside the cavities of the frame, thereby eliminating convective heat exchange between the outer and inner cladding. In turn, a deaf internal vapor barrier prevents cold air infiltration and protects the insulation from moisture.
At first glance, everything is simple, but an idea alone without correct implementation cannot be a guarantor of outstanding performance. When examining a randomly taken frame house in Russia, you can see the frame on wooden racks, and vapor barrier, and cotton wool inside the walls. But the density of the filler is far from optimal, the filling of the cavities is done incorrectly, and the vapor barrier is not airtight: all this leads to a decrease in thermal insulation properties, the formation of large thermal bridges and condensation zones.
Frame system requirements
The basis for the correct insulation of the “frame” is a well-designed supporting system. A number of requirements are imposed on it:
- Correct stance pitch. The norms provide for an axial distance of 300, 400 or 600 mm, but in fact the space between the racks should be such that the insulation of the selected format is installed on the spine. In other words, the distance between the opposite surfaces of the timber should be 4-5% less than the width of the mat indicated on the package.
- Frame configuration. The standard option is considered to be a series of uprights with double-sided plating, which gives the system a diagonal stiffness. However, the racks themselves are quite large thermal bridges; in regions with very cold climates, with such a configuration, it is impossible to provide low thermal conductivity. There are three options:
- Cross-insulation is suitable for buildings without rigid cladding. The outer strapping is performed with horizontal square beams with the thickness of the main posts. Mineral wool is inserted between the battens, thus reducing the number of thermal bridges to the number of crossings of the frame elements.
- Composite posts with a thermal break in the form of a porous layer. On the Russian market, such material is practically not found..
- Double-row frame with offset racks. The best option for northern harsh regions: in addition to completely eliminating direct bridges of cold, a twofold increase in the maximum thickness of the insulation is provided (up to 300 mm).
- Compensation for cotton wool shrinkage. The code of practice provides for a maximum wall height of 3 m. This is done to limit the weight of the vertical column of cotton wool, but such recommendations are only valid for high-class materials that can hold their shape. When using ordinary insulation, you should arrange partitions of thin plywood or plastic mesh between the racks to support the insulation. The distance between the jumpers is from 80 to 140 cm, depending on the density and thickness of the cotton wool; to minimize insulation waste, spacers should be installed with an offset as the frame is filled.
Laying insulation into walls
Of fundamental importance is how the insulation is laid in the cavity of the frame and whether the choice of density and type of mineral wool was made correctly. Let’s start with the latter: only cotton wool with a phenol-formaldehyde binder that retains its shape well is suitable for insulating frame houses. Ideally, the binder has a wax base, ostensibly for environmental reasons, although the penetration of volatile substances into the building is absolutely impossible..
Abroad, it is customary to choose mineral wool according to the thermal resistance index, it must be at least R20, this is the minimum value for 4.5 thousand degree-days of the heating period (GSOP). In some regions of Russia, GSOP reaches 6-7 thousand, which forces the use of insulation with the R40 and R45 index, respectively.
Note: the R index should not be confused with the fire resistance index, which has the same designation in the domestic material classification.
Thermal resistance marking is not used for heaters found on the domestic market, therefore, one has to be guided by the concepts of thickness, density, thermal resistance value and summary data from SNiP 31-02 and SNiP 11-3. Thus, a full-fledged thermal protection of a frame house becomes impossible without carrying out a comprehensive heat engineering calculation.
You can go another way: neglecting the economy, make the thickness of the insulation excessive. With this approach, you can correlate the thickness of mineral wool with a density of 50 kg / m3 with a cold five-day temperature as follows:
Temperature of the coldest five-day week, ° С Recommended insulation thickness, mm up to -14 90 up to -17 140 up to -22 90 + 90 up to -30 140 + 90 up to -38 140 + 140
These ratios take into account the standard rack cross-section recommended by the adapted standard for frame houses. The last three points correspond to a two-row frame with an offset position of the posts.
The laying of cotton wool in the cavity of the frame should be done in dry and clear weather in order to avoid saturation of the insulation with moisture. The cells formed by the support struts must be filled completely without voids or gaps. For this, it is recommended to use low-density cotton wool (25-30 kg / m3), tearing it into small flaps, which are used to caulk the cracks at the racks and in the corners.
Filling the walls is not the only option for insulating a frame house. It is possible to arrange external thermal insulation, but its material must have the ability to pass steam into the external environment. As a rule, for this purpose, wood-mineral boards of the “Isoplat” type are used, but this is only an auxiliary measure used to shift the dew point or as an increase in thermal protection..
When humid air gets inside the heat protection belt, moisture condensation occurs in the area where the cotton wool has a sufficiently low temperature. When wet, the insulation loses its properties, shrinkage increases, and the process of condensation is gaining intensity. To avoid such phenomena, all frame houses have an extremely high degree of isolation of the internal environment from the external.
First of all, you need to prevent the mineral wool from getting wet during the construction process. The frame structure of the walls allows you to do this quite easily: after filling the next cell, it is closed on two sides: with a gas-tight film from the inside and a diffusion material outside, about which our site sovetov.ru already wrote. The latter is performed in order to ensure the release of residual moisture into the atmosphere, where the partial pressure of water vapor is lower than in the thickness of the wall through which the residual heat flux passes. This is an effect akin to when warm wet clothes dry out in frosty air almost instantly..
Internal vapor barrier is made with a dense polyethylene film. It is allowed to fasten it to the frame racks with staples, on top of the fastening strip should be sealed with a tape of plastic tape. This method is also suitable for waterproofing the lower plane of floors. The joints between the sheets of the film can be oriented to the location of the racks, where high-quality mechanical fastening can be provided. However, this often results in a lot of scraps, so the preferable option is to solder the joints with a special sealer for plastic bags.
Insulation of floors and roofs
The insulation of the walls and roof above the attic is carried out using the same technology with the only difference that it is very difficult to securely fix the cotton wool in an inclined position. High-density mats can be used, which are inserted into the spacer with a tolerance of about 10%, but in this case the cotton wool must be reinforced. It is also possible to use a polymer mesh as a measure of temporary support, in which case you can use cotton wool with a density of 40-50 kg / m3, with lower thermal conductivity.
It is customary to use bulk insulation in the ceilings of a frame house. This has a positive effect on both the cost and the degree of noise absorption of the floors between floors. On the lower side, a waterproofing film acts as a protective barrier, on the upper side there is a synthetic burlap, which prevents cotton wool from blowing out during dynamic floor vibrations. Both barriers should be as tight as possible.
The most problematic node in the thermal protection of a frame house is the Mauerlat area, where the rafter system is connected to the floor girders or crossbars of the wall frame. The use of mineral wool in this area is hampered by the large amount of scrap and low manual filling efficiency. The best option is to spray with polyisocyanurate foam, which provides additional fire resistance of the upper zone of the wooden structure. In one-story houses, it is allowed to use polyurethane foam for the same purposes..
The second problem area is the joints in the area of openings. If the main heat protection belt is made according to all the rules, the seams along the contour of windows and doors can account for up to 30-40% of residual heat loss. To avoid this, direct contact between the frame system and the window unit should be excluded. This can be achieved by using a foam seam with a thickness of at least 30 mm or a flashing made of EPSP panels along the abutment contour. At the same time, it is extremely important to continue the thermal cutoff towards the interior of the building, arranging insulated slopes.