Conn. Gen. Stat. § 47-281: Substantial completion of units required.

In the case of a sale of a unit in which delivery of a public offering statement is required, a contract of sale may be executed, but no interest in that unit may be conveyed, until the declaration is recorded and the unit is substantially completed, as evidenced by a recorded certificate of substantial completion executed by a registered architect, surveyor or engineer, or by issuance of a certificate of occupancy authorized by law.