Waterproof vapor permeable membrane is a layer of membrane laid outside the building insulation layer. While strengthening the air and water tightness of the building, it also allows the envelope and indoor moisture to be discharged, so as to achieve energy conservation, improve the building durability and ensure the indoor air quality. The specific principle is described as follows.
1.1 Strengthen air and water tightness of buildings
Practice has proved that no matter what kind of facade form or roof laying form is used, the enclosure structure cannot be sealed. As for the exterior wall, it is difficult to avoid the cracking of the plastering, to tightly lap the hanging plate, and even more difficult to achieve the simple masonry block "Impervious wall". These problems can be found at the internal and external corners, joints and doors and windows It is more obvious around. Through these non closed pores, air flow and water vapor can invade the enclosure structure, which has a serious impact on the energy consumption, durability and comfort of the building.
1.1.1 Building energy consumption
——Rainwater and moisture entering the envelope with airflow will reduce the effective thermal resistance of the insulation layer, resulting in more energy consumption. Of course, the influence of water vapor on different insulation materials is different.
——The intruded airflow will form convection circulation inside the building envelope, and will also reduce the effective thermal resistance of the insulation layer, resulting in more energy consumption. Similarly, the influence of air flow on different insulation materials is different.
——When air flows into the room, people will have to use larger HVAC equipment to compensate for the heat/energy loss, thus increasing building energy consumption.
1.1.2 Building durability
The water vapor intruding into the enclosure will lead to wall Cavities form vapor condensation, accelerating the aging of building materials, such as steel corrosion and wood decay, which has a serious impact on the durability of buildings.
1.1.3 Building comfort
——The invasion of air flow will adversely affect the indoor thermal comfort;
——Bring pollutants deposited on different building components and radiation from building materials or outdoor, thus affecting indoor air quality;
——The water vapor entering the building envelope creates conditions for the condensation of water vapor in the envelope, leading to the formation of mold, which affects the indoor air quality and the health of residents.
It can be seen that strengthening the air tightness and water tightness of buildings is crucial to building energy conservation and environmental protection.
1.2 Building vapor permeability.
Due to the temperature difference between indoor and outdoor, it is difficult to avoid the condensation inside the building envelope. However, in fact, only when the enclosure structure is always in a wet state will it cause moisture problems, resulting in adverse effects on building energy consumption, durability and comfort (as mentioned above). Therefore, in order to avoid the occurrence of problems, ensure the vapor permeability of the building, so that it can achieve natural drying by diffusing water vapor to the outside, it is particularly important.
To sum up, the energy consumption, durability and comfort of buildings are closely related to the air tightness, water tightness and vapor permeability of their enclosure structures. The waterproof and vapor permeable membrane technology is to achieve the goal of saving energy consumption, protecting the living environment and improving the durability of buildings by controlling the above factors. At the same time, with the use of the air layer, it can more effectively ensure the dryness of the maintenance structure (exterior wall and roof), and play a significant heat insulation effect.
