Hardwood Floors Oct/Nov 2019

BuildingThermal Envelope What happens with the exterior climate also will affect the indoor conditions of the space. The BuildingThermal Envelope includes everything within the basement walls, exterior walls, floor, roof, and any other building element that encloses conditioned space. Conditioned space is defined as an area or roomwithin the building that is intentionally heated or cooled, and humidified or dehumidified, to be maintained at the same expected conditions as the living/interior space either for the comfort of occupants, or for preserving temperature and humidity-sensitive goods (wood floors). Unconditioned space refers to exterior space, or a space within the shell of a building, that is uncontrolled, and is neither directly nor indirectly heated, cooled, humidified, nor dehumidified. The exterior conditions (unconditioned spaces) of a building affect how a building is built to keep the interior from being negatively affected by adverse exterior conditions. This involves building practices that control the flow of moisture vapor, most of which are detailed in local building codes. In order to understand howmoisture vapor moves into and through the building, and ultimately can affect the wood flooring system, it is important to know which direction heat, air, and moisture vapor are likely to flow.

Vapor Drive Moisture vapor migrates through materials by diffusion. The law of thermodynamics states that temperature moves from a warmer space to a cooler space. This type of moisture transport is called thermally driven diffusion . The moisture vapor moves from the warm side of the building assembly to the cold side of the building assembly. Building interiors are affected by two distinct seasons – heating and cooling. a) In the summer and hot/humid climates, during the interior cooling season, vapor drive is predominantly inward. Cooling systems lower the temperature of the interior air. Cooling the air decreases its ability to hold moisture, and the interior relative humidity naturally increases. Fortunately, air conditioning cools the air by removing moisture through condensation. b) In the winter, during the interior heating season, vapor drive is predominantly outward. Heating systems raise the temperature of

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the magazine of the national wood flooring association

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