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The function of a vapor barrier is to retard the migration of water vapor. A vapor barrier is not typically intended to retard the migration of air. This is the function of air barriers. [8] Air is mixed with water vapor. When air moves from location to location due to an air pressure difference, the vapor moves with it.
Condensation comes from water vapour within the building. Common sources may include cooking, bathing, dishwashers, etc. The moisture in the air condenses on cold surfaces, sometimes inside the walls called interstitial condensation. Buildings with poorly insulated walls are very prone to this problem.
Interstitial condensation is a type of condensation that may occur within an enclosed wall, roof or floor cavity structure, which can create dampening. When moisture -laden air at dew point temperature penetrates inside a cavity of the structure, it condenses into liquid water on that surface.
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Wall flashing is typically found at interruptions in the wall, such as windows and points of structural support. Sill flashing (or sill pan) A concealed flashing placed under windows or door thresholds to prevent water from entering a wall at those points. Roof penetration flashing Used to waterproof pipes, supports, cables, and all roof ...
The difference can be illustrated by the fact that an insulated attic floor is the primary thermal control layer between the inside of the house and the exterior while the entire roof (from the surface of the roofing material to the interior paint finish on the ceiling) is part of the building envelope.
During the winter, ACH may range from 0.50 to 0.41 in a tightly air-sealed house to 1.11 to 1.47 in a loosely air-sealed house. [12] ASHRAE now recommends ventilation rates dependent upon floor area, as a revision to the 62-2001 standard, in which the minimum ACH was 0.35, but no less than 15 CFM/person (7.1 L/s/person).
Rooftop HVAC unit with view of fresh-air intake vent Ventilation duct with outlet diffuser vent. These are installed throughout a building to move air in or out of rooms. In the middle is a damper to open and close the vent to allow more or less air to enter the space. The control circuit in a household HVAC installation.