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A vapor barrier on the warm side of the envelope must be combined with a venting path on the cold side of the insulation. This is because no vapor barrier is perfect, and because water may get into the structure, typically from rain. In general, the better the vapor barrier and the drier the conditions, the less venting is required. [7]
Housewrap (or house wrap), also known by the genericized trademark homewrap (or home wrap), generally denotes a modern synthetic material used to protect buildings. Housewrap functions as a weather-resistant barrier , preventing rain or other forms of moisture from getting into the wall assembly while allowing water vapor to pass to the exterior.
Open-cell foam is porous, allowing water vapor and liquid water to penetrate the insulation. Closed-cell foam is non-porous, and not moisture-penetrable, thereby effectively forming a semi-permeable vapor barrier. (N.B., vapor barriers are usually required by the Building Codes, regardless of the type of insulation used.
Epoxy moisture control systems can be used when these tests determine that the moisture vapor emissions need to be remediated in order to install the selected floor covering within the timeframe allotted by the construction schedule. Epoxy moisture control systems are roller-applied and are available in one-coat and two-coat varieties.
A damp-proof course (DPC) [2] is a barrier through the structure designed to prevent moisture rising by capillary action such as through a phenomenon known as rising damp. Rising damp is the effect of water rising from the ground into property. [3] The damp proof course may be horizontal or vertical. [4]
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. [11]
The passivhaus standard combines superinsulation with other techniques and technologies to achieve ultra-low energy use.. Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss (and gain) by using much higher insulation levels and airtightness than average.
In March, 2008, the city of Portland, Oregon, granted a waiver of the requirement for a vapor barrier or retarder when using cellulose insulation. [11] This appeal cited industry guidance that the combination of an exterior vapor retarder (as required by code) and an interior one could trap moisture in the wall, leading to damage.
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