<P> 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 : 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 . </P>
<P> 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 : 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 . </P>
why is vapor barrier on the warm side
why is vapor barrier on the warm side
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 .
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 .