Where should vapor retarder layers typically be placed in insulated construction?

The correct placement of vapor retarder layers in insulated construction is on the warm side of the insulation. This is crucial because the primary function of a vapor retarder is to prevent moisture-laden warm air from traveling into the insulation and condensing within the colder layers of the wall assembly. By placing the vapor retarder on the warm side, it effectively reduces the likelihood of condensation that can lead to mold growth, insulation degradation, and wood rot, thus helping to maintain the integrity and performance of the building envelope.

When moisture-laden air rises and comes into contact with cold surfaces, it has the potential to cause issues within the building structure. If the vapor retarder is positioned incorrectly, for instance, on the cold side or in the middle of the insulation, it could allow moist air to pass through, leading to condensation problems as mentioned before. Therefore, proper placement is critical for maintaining the dry and effective insulation properties of the construction.