A vapor retarder is not required for detached structures accessory to occupancies in which group?

A vapor retarder is typically used in building construction to reduce the movement of moisture through the building envelope. However, regulations can vary depending on the occupancy type and the specific requirements of the building codes.

In the context of detached structures that are accessory to certain occupancies, the requirement for a vapor retarder is relaxed for residential buildings classified as Group R-3. Group R-3 typically includes structures such as single-family homes or duplexes that are not used for commercial purposes, thus making the moisture management less stringent. Since these structures are often smaller and less complex than larger commercial buildings, the potential risks associated with moisture accumulation can be considered lower, leading to the conclusion that a vapor retarder is not necessary in such cases.

In contrast, the other groups listed (A-2, I-3, and S-1) usually represent occupancy types that have larger areas, higher capacities of usage, or specific requirements related to moisture and air quality control, which warrant the inclusion of vapor retarders to protect both the building and occupants from potential moisture-related issues.