Why House Wrap
As the "Building Regulations" requires the continuous improvement of thermal efficiency in commercial and residential buildings, the tightness of the building envelope is getting better and better, which must have a lot of benefits for building energy saving.However, in such a building, water control and management becomes crucial.
Introduced in the late 1980s, the "house wrap" has become an important part of the construction industry.However, there are many types of breathing membrane."Breathing membrane" for wood-frame structure should have a vapor resistance of 0.6mns/g or less;For the "breathing membrane" used on the roof, the vapor resistance is 0.25MNs/g or less.The lower the vapor resistance, the better the permeability of the "breathing membrane".The better the air permeability is, the more effectively the "breathing membrane" can discharge the water vapor from the wall and keep the wall system dry.
All indoor activities, including cooking and washing, produce a lot of water vapor.This water vapor must be well managed to ensure the life of the building and the health of the indoor living environment.The installation of "waterproof breathing membrane" enables the house to achieve these effects.
Waterproof breathable membranes allow excess moisture from the insulation to be easily released into the atmosphere and keep the interior of the wall and roof structures dry.In addition, Waterproof breathable membrane is also called the second protective layer of the house,preventing external environmental impurities (such as dust and rain) from penetrating into the structure of the house.The installation position of these membranes is the exterior of the sheath wall and the interior of the roof tiles or cladding board, the cold side or the outer side of the insulation.
If no membrane is used, the impurities (wind, rain or dust) generated from the outside will penetrate the internal structure of the walls or roof, causing damage and poor performance.The purpose of the breather membrane is to prevent these impurities from adversely affecting the building. But in order to make the building to perform this task with breathability, the waterproof breather membrane must be breathable.Simply using a polythene plastic sheet as a roof or wall membrane would be a powerful barrier against external environmental conditions, but the moisture generated from interior would remain in the enclosure structure, causing immeasurable damage.
Key Points to Judge Air Barrier:
1. Waterproof: although waterproof breathable Air Barrier can not have the same waterproof performance as polyethylene plastic sheet, the ordinary quality of waterproof breathable Air Barrier should reach at least 1.5m water column without water leakage.Such waterproof and breathable Air Barrier can be called a high-quality waterproof and breathable Air Barrier.
2. Water vapor transmission: according to the requirements of different areas,people use air barrier with different water vapor transmission rate. There is an important tip. A good air barrier need a good installation method. There must be an air layer outside the air barrier.Because there is a lot of water vapor from the internal structure and condense on the air barrier into water droplets. The evaporation of water is usually in two conditions. One is with air flow; the other is with temperature rise. When there is an air layer on the outside of the air barrier, even in the shade where the temperature is not too high, it can also produce a slight air flow inside the air layer and cause the water to evaporate smoothly.If the air barrier is attached to the cladding tightly, especially on the shady side of the house, where the sunlight is not available and the temperature often fails to reach the evaporation temperature, the cladding will block the flow of air and slow down the evaporation of water.
3. Resistance to penetration of air: a good roof membrane should also be a good air barrier.The resistance to air or wind varies with the type of roof membrane.
4. Tensile strength: a product with high tensile strength can withstand the test of external wind force and internal tensile force.