Thermal insulation structure of building dry facing?

What is the specific content of thermal insulation structure of building dry facing? Zhong Da Consulting will answer your questions below.

Building dry facing is relative to the wet construction method of plastering or pasting facing with mortar (including building glue). This classification method is the Japanese external wall insulation classification method when I was studying in Japan. The difference is that an air layer will be formed between the facing layer and the insulating layer. The external insulation system of opaque curtain wall commonly used in China is a typical practice of this method, including decorative surfaces and insulation layers such as metal and stone curtain wall, wood-based panel curtain wall and PVC hanging plate (chain nail), and the main structure is dry-hung by fixed parts. Compared with the wet external thermal insulation system, the dry facing technology reliably connects the facing material with the main structure through embedded parts, keels and fasteners, which makes the load transfer clearer and clearer, improves the firmness and safety of external facing installation, and has good building effect. Because the keel can form an air layer which is connected with the outside and can flow between the facing material and the thermal insulation material, the thermal insulation effect of the wall can be improved. Also, because the keel can partially weaken the insulation layer, resulting in a thermal bridge, and if the insulation material is improperly selected or poorly protected, it will cause a fire in the construction. Therefore, special attention should be paid to the selection of thermal insulation materials and the structure of joints. 1 influence on insulation layer 1- 1 reduces the summer ambient temperature and improves the durability of insulation system. In common thermal insulation materials (polystyrene board, extruded board, rigid polyurethane spraying), the external thermal insulation system of the external wall is placed on the outside of the external wall, and the crack-resistant protective layer on the outside of the thermal insulation layer is only 3~ 10mm, which directly bears the nature. Due to the large thermal resistance of thermal insulation materials, the heat of the protective layer is not easy to spread through conduction. In summer, under the sunshine, the temperature change speed of the thermal insulation and anti-crack protective layer of the external wall is 8~30 times higher than that of the main body without thermal insulation, and the temperature can reach 80℃. However, when the temperature of polystyrene board exceeds 70℃, irreversible thermal shrinkage deformation will occur, leading to more serious cracking deformation. This situation is more obvious in dry and high temperature areas and rainy areas where the weather changes rapidly. Direct ultraviolet rays, oxygen, carbon dioxide and moisture in the air will destroy the organic bonding materials of the protective layer, accelerate the aging of thermal insulation materials such as benzene board and affect the durability of the system. This is also the reason why cracks are more likely to appear in the external wall with direct sunlight in engineering examples. The dry facing layer plays a good role in shading and heat insulation of the insulation layer in summer. The flowing air layer formed outside the insulation layer can also reduce the influence of solar radiation and the surface temperature of the insulation layer, take away the heat generated by the heating of the facing layer through the air flow, effectively avoid the deformation of the insulation layer and the cracking of the protective layer, and improve the durability of the insulation system. 1-2 Reduce the influence of wall air tightness and rainwater infiltration on thermal insulation performance. In general, whether brick-concrete structure, frame or reinforced concrete shear wall bear the load, the main structure of the building has high thermal resistance and high air tightness. Vapor permeation resistance makes indoor water vapor not produce condensed water between decorative layer and thermal insulation material, and thermal insulation material is not affected by moisture. However, in actual construction, when building load-bearing bricks and blocks, especially frame-filled walls, the mortar joint is often not full, which greatly reduces the air tightness of buildings. In winter, indoor water vapor will penetrate into the benzene board through the mortar joint, which will cause the insulation material to be damp and reduce the insulation effect. If the decorative layer is airtight at this time, there will be no way out for water vapor, and it will freeze and thaw, resulting in cracking and hollowing of the decorative layer until it falls off. At the same time, when the decorative protective layer cracks, rainwater and even snow melt water will penetrate into the insulation layer, causing water seepage and cold seepage, accelerating the emergence of cracking and hollowing. A large-scale residential area built in Songbei, Harbin in 2004 found many water seepage phenomena on the external wall in 2008, and it was difficult to maintain because the water leakage point could not be found. Harbin Fa [2009] 17 requires that the outside of the wall at the grass-roots level should be leveled with 20-thick 1:3 cement mortar before the thermal insulation layer can be constructed, which is also to avoid this phenomenon. When the decorative layer is dry-hung, the flowing air outside the insulation material will constantly take away the water vapor, keep the insulation layer dry and maintain the lasting insulation effect of the insulation layer; The seams of the veneer are open, and the air layer is under the same pressure as the outside air, which can effectively prevent rainwater from infiltrating into the flowing air layer, not to mention the insulation layer. 1-3 local thinning of insulation layer is easy to cause thermal bridge. No matter what kind of veneer, it needs to be nailed to the keel at a certain distance when it is dry hung. The keel is connected with the main structure through embedded parts, which will partially penetrate the insulation layer, making the insulation layer at the keel thinner, locally generating thermal bridges or increasing the heat transfer coefficient of local external walls. 1-4 construction is more prone to fire. When steel keel is used, the general process of construction is to install the main keel-lay insulation layer-weld the secondary keel-install connectors and plates. If foam insulation is used, welding sparks can easily ignite the insulation and cause fire. The general structure of dry facing depends on the type of external facing material. General exterior decoration materials include wood-based panels, steel plates, stones, dry tiles, etc. When using profiled steel plate or PVC hanging plate that can form ventilation layer, use plastic and wooden keel with low thermal conductivity, leave a groove on the outside of the insulation board, press it into the insulation board to be flush with it, and nail the decorative board on the keel. The technology of the complete system in the market is mature, with special fittings such as corner, end and convergent end, and the fixed parts are made of engineering plastics, which can isolate the thermal bridge and make the system complete. When the decorative panel is made of aluminum-plastic board, cement fiberboard and other light plates, light steel keel should be adopted and located outside the insulation layer. The horizontal or vertical cavity formed by the gap of the keel is used as the ventilation layer, and the keel is fixed on the load-bearing wall with hardware, and the supporting hardware mostly adopts bridge breaking technology such as engineering plastic nails. Dry hanging of stone is a common external decoration method, and the air layer is large, so polyurethane foam is generally used to partition the keel thermal bridge; Dry-hung tiles are close to dry-hung stones, and the supporting backboard of tiles is dry-hung on the keel. The grooves on the back plate are used to fix the tiles, supplemented by adhesive tape to ensure their firmness, and the gaps of the tiles are caulked with mucilage to avoid rainwater infiltration. Thermal insulation materials are usually installed on the construction site, such as benzene board, extruded board and polyurethane board. , and fixed on the main external wall by pasting or anchoring. Protective layer should be set, which is only used to prevent moisture and aging, and is beneficial to fire prevention during construction and use. You can also choose other thermal insulation materials with high moisture permeability, such as rock wool, glass fiber and mineral wool. And fixed on the main external wall by mechanical fixing, which has the advantage of good fire resistance. 3 design considerations Taking the design of an office building as an example, this paper introduces the design considerations of stone curtain wall. 3- 1 Material Selection and Structure Office Building 12 floor, frame structure, 3-6m high, office bay 3-9m. The infilled wall is a concrete hollow block, and the exterior decoration is a stone curtain wall. The finished glass wool felt is selected as the thermal insulation material, and its combustion performance is Class A incombustible material, thus eliminating the fire hazard. The outer surface of the finished cotton felt is covered with a wind-proof and waterproof breathable film, so that the water vapor in the material can be taken away by air; A vapor barrier film is provided on the inner surface to prevent indoor water vapor from penetrating. This is because the low-density cotton building insulation material is easy to absorb moisture during use, which leads to a significant increase in thermal conductivity and affects the insulation effect. The thermal conductivity of glass wool is 0-039W/m2-k, and when the calculated thickness is 85mm, it can meet the requirement of thermal conductivity of external wall of 0-45W/(m2-k). Considering the factors such as concrete beam-column position and 50-thick polyurethane foam of main keel, the design thickness is 100mm, and the thermal conductivity of external wall is 0-425 w/(m2). During construction, 200- 150-8 steel plates are embedded on the frame beam with the spacing of 1-5~2-4m, one above and one below the beam; Angle code and embedded plate are welded in pairs; After spraying 50-thick polyurethane foam in the gap of the corner code, the vertical 8# channel steel main keel is fixed with bolts through the corner code, leaving a gap of 50mm between the keel and the wall, and spraying 50-thick polyurethane foam for thermal insulation; Fix the glass wool felt on the wall beam with nylon anchor bolts, with the number of 5-7 pieces/m2; Use bolts to fix pairs of angle steel angle codes through the main keel, and the spacing is 600mm, which is consistent with the size of stone. Fix the other end of the angle code with the transverse secondary keel of 5# angle steel with bolts; Install the L-shaped aluminum alloy main pendant and the U-2 anchor in the back slot, and install the 30-thick granite fireproof board, as shown in figure 1. 3-2 Design Points: The weight of thermal bridge should be considered in the calculation of thermal insulation material thickness, and the influence of linear heat transfer coefficient should also be considered in residential buildings, and the thermal insulation thickness of the main section of the wall should be appropriately increased. Attention should be paid to the structural treatment of wall-attached components that are prone to thermal bridge, such as keel embedded parts and connectors, and space should be left between the main keel and the wall (beam) to place thermal insulation materials; The secondary keel is outside the insulation layer or wrapped between the insulation layers; The embedded parts are in the insulation layer; The connector is wrapped. After the installation of thermal insulation materials in construction, the connection of steel structure should be tightened with screws as far as possible to avoid electric welding sparks igniting the thermal insulation materials. Conclusion Building dry facing is a diversified way based on recycling, which has irreplaceable advantages in safety, durability and aesthetics, and has broad application prospects.

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