Del. Code tit. 25, §§ 81-420

In the case of a sale of a unit for 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 an independent registered architect or engineer, or by issuance of a certificate of occupancy authorized by law.