Are vapor barriers required in SIP buildings?

Air barriers or vapor barriers are not required in SIP buildings because properly sealed SIPs create a code-compliant air barrier with a permeability rating of less than 1.0 perm. In addition, the foam core of SIPs is solid and continuous throughout the wall, eliminating the convection and condensation issues that can occur in cavity walls.

This should not be confused with the requirement for external water-resistant barriers that protect all external wood structures from bulk water. See the Builder's Guide to SIPs by Joseph Lstiburek for detailed recommendations on vapor barriers.