why is vapor barrier on the warm side
Vapor barrier An interior vapor retarder is useful in heating-dominated climates while an exterior vapor retarder is useful in cooling-dominated climates. In most climates it is often better to have a vapor-open building assembly, meaning that walls and roofs should be designed to dry:[6] either to the inside, the outside, or both, so the ventilation of water vapor should be taken into consideration. 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]
Thermosphere The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat. A normal thermometer might indicate significantly below 0 °C (32 °F), at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact. In the anacoustic zone above 160 kilometres (99 mi), the density is so low that molecular interactions are too infrequent to permit the transmission of sound.